Papers by Muammer Ozgoren
The three-dimensional vortical structures formed in the wake region downstream of a road vehicle ... more The three-dimensional vortical structures formed in the wake region downstream of a road vehicle and the change of the structures by the effect of an spoiler were investigated using dye visualization and the particle image velocimetry techniques. The measurements were carried out in open water channel for specific Reynolds number values of based on the vehicle length and several visulization planes parallel to the free stream flow were used to obtain more detailed flow fields. All these measurements provide a detailed quantitative description of highly complex and time dependent nature of the flow around vehicle with and without a spoiler. Flow characteristics have been examined in terms of the 2-D instantaneous and timeaveraged velocity vectors, patterns of vorticity, streamlines, rms of velocity fluctuations and Reynolds stress variations and discussed from the point of flow physics, vortex formation in both cases with and without a spoiler. The results show significantly differen...
Debi ölçümü konusunda, özellikle akademik çalışmalarda, sıklıkla yurtdışından ithal edilen
debime... more Debi ölçümü konusunda, özellikle akademik çalışmalarda, sıklıkla yurtdışından ithal edilen
debimetreler kullanılmaktadır. Bu cihazlar bilgi maliyeti, navlun, vergiler gibi maliyetlerden dolayı
kullanıcı için pahalı bir çözümdür. Ayrıca genellikle stok tutulmadığı için kullanıcının 4 ila 8 hafta gibi
uzun süreler beklemesi gerekmektedir. Bununla beraber gelen ürünlerin kullanımında, bir arıza
durumunda müdahalede ve kalibrasyon konularında sınırlı teknik destek söz konusudur.
Bu çalışmada ithal debimetrelere alternatif olarak geleneksel ventüri tüpü ve bir elektronik veri toplama
düzeneği kullanarak debi ölçümü ve sonuçları incelenmiştir. Biri sıvı diğeri ise gaz olmak üzere iki
farklı akışkanın debilerinin ölçülmesi için iki farklı ventüri tüpü hazırlanmıştır ve aynı elektronik veri
toplama düzeneğinde ölçümler kaydedilerek hesaplamalar yapılmıştır. Akışkanlardan gaz olan hava,
sıvı olan ise ST42 numaralı endüstriyel yağdır. Yağ akışkan, ölçümler sırasında 100 oC sıcaklığa
kadar ısıtılmıştır. Çalışma sonuçlarına göre ventüri tüpünün dinamik debi ölçümünde dahi etkin
biçimde kullanılabileceği gösterilmiştir.
Binalarda ve diğer birçok endüstriyel alanda yaygın olarak kullanılan kompakt ısı değiştiricileri... more Binalarda ve diğer birçok endüstriyel alanda yaygın olarak kullanılan kompakt ısı değiştiricilerinin
seçiminde önemli kriterler ısı transferi ve basınç düşüşü performansı, maliyet, kompaktlık ve etkenlik
olarak sıralanabilir. Bununla birlikte son yıllarda enerji kullanımına yönelik yapılan çalışmalar farklı
sistemlerdeki enerji kullanılabilirliğinin yani ekserjinin de değerlendirilmesi gerektiğini ortaya
koymaktadır. Aynı zamanda ikinci yasa yaklaşımı, bir optimizasyon problemi olan ısı değiştirici
tasarımında da yer almaktadır.
Yapılan çalışmada 650-670 kompaktlık oranına sahip üç farklı tipteki ısı değiştirici 0.027-0.16 ısıl
kapasite oranlarında deneysel olarak incelenmiştir. İnceleme sonuçları kullanılarak ısı değiştiricilerinde
gerçekleşen ekserji yıkımı hesaplanmıştır. Ekserji yıkım değerleri açısından ısı değiştiricileri
karşılaştırılmıştır. Karşılaştırma sırasında ısı değiştiricilerin ısı transferi yüzey alanlarının dağılımı,
tersinmezlik değerleri, tersinmezliğin sıcaklık ve basınç bileşenleri ve ekserji verimleri kullanılmıştır.
Heat transfer and pressure drop performance, cost, compactness and effectiveness can be listed as
important criteria for selection of widely utilized compact heat exchangers in buildings and a lot of
other industrial areas. Nevertheless, recent studies intended for energy usage presents that usability
of the energy, namely exergy, should be evaluated for various systems. The second law approach is
also used for heat exchanger design which is an optimization problem.
In this work, three different type heat exchangers having 650-670 compactness ratios were
experimentally investigated between 0.027-0.16 heat capacity ratios. Exergy destruction occurred in
the heat exchangers were calculated using the investigation results. Distribution of heat transfer
surface area of the heat exchangers, irreversibility rates, temperature and pressure components of the
irreversibility and exergy efficiency were used for comparison.
Cylindrical geometry with circular cross section is used in a lot of industrial
applications such... more Cylindrical geometry with circular cross section is used in a lot of industrial
applications such as bridge legs, electricity production from vortex induced
vibrations, petroleum and natural gas lines, off-shore and on shore structures and
wind turbine bodies. Flow structures around these geometries have important effects
on forces acting upon these geometries. Therefore, performances of industrial
designs can be improved by controlling flow structure.
Experiments were carried out in an open water channel at Mechanical
Engineering Department of Selcuk University. In the present study, flow structure
around a cylinder with circular cross section was investigated via Particle Image
Velocimetry (PIV) technique in uniform flow condition. Thereafter a knitted porous
structure was wrapped around the cylinder in order to apply a passive flow control in
the wake structure of the cylinder. Free stream velocity during the experiments was
arranged as the Reynolds number based on the cylinder diameter of 50mm was
10000. Velocity vector field, streamline topology, streamwise velocity components
and Reynolds stress correlations were used in order to explain flow structure around
the cylinders for the sake of comparison. At the end of the experiments, it was
realized that the porous knitted structure extended the size of wake and elongated
wake length of the cylinder and increased the velocity distributions in the wake
while decreasing the strength. The wake was extended approximately half cylinder
diameter in width and elongated approximately one cylinder diameter in length
when the passive flow control was applied. The size of foci points in the wake of the
cylinder without passive control were evaluated as they were relatively small
comparing to the that of the cylinder with passive control. In the wake of the
cylinder with passive control, a saddle point occurred in the further downstream
comparing to the wake of the cylinder without passive flow control. This study
presents to control the flow around a circular cylinder through the implementation of
artificial surface roughness by a knitted coating around the cylinder, which has a
good agreement from the point of flow physics in the literature. These results will be
useful for industrial applications, ocean engineering and ocean energy production
via various similarity approaches. In the future, the knitted structure forming
circular, diamond or trapeze patterns will be tested.
A lot of solutions for the flow applications have been developed by the help
of basic fluid dynam... more A lot of solutions for the flow applications have been developed by the help
of basic fluid dynamics research. These basic researches include experimental flow
field measurements and also computational fluid dynamics (CFD) analyses. A
particular part of aforementioned studies focus on ocean structures, particularly used
in energy generation, since they contains various basic geometrical shapes. Results
are often presented flow characteristics as free stream velocity, pressure values and
vibrations, vortex induced vibrations. Time Averaged Particle Image Velocimetry
(PIV) is one of the experimental measurement techniques. This technique comprises
instant and time averaged measurement of a complete flow field in respect of flow
velocity. Instant and time averaged vector field, stream lines, scalar value distributions of velocity fluctuations, Reynolds stress correlations, normalized u and
v velocity components and vorticity can be derived.
In this study, two independent spheres were placed in a turbulent boundary
layer in a 30 degree angled tandem position in order to simulate an ocean bottom
situation and interaction between boundary layer and wake regions of the spheres
were investigated with a PIV setup. Results were presented with visual and scalar
data. Thirty five different angled tandem array sphere positions were investigated
experimentally in boundary layer flow for instantaneous velocity vectors, time
averaged velocity vectors, stream lines, scalar values of velocity components, their
RMS values, Reynolds stress. Boundary layer greatly effects flow pattern, especially
when spheres were located within the boundary layer. Different distances between
the spheres yielded dissimilar results. After a specified height from the surface,
evolution of the flow patterns depended to the gap between spheres were
approximately predictable, which is also an indication to ineffective boundary layer
flow. The instantaneous vorticity fields reveal an unsteady wavy structure of the
sphere wake. The concentration of small scale vortices (eddy) is more dominant in
the wake of the sphere when the gap is initiated. It is demonstrated that the presence
of boundary layer flow over the flat plate generates significant complications into
the wake of the spheres due to non-uniform velocity profile, gap flow between the
bottom section of the spheres and flat plate surface. The non-uniform velocity
profile of the boundary layer flow causes a difference in the celerity of the vortex
shedding from the periphery of the spheres. Owing to the jet flow, the periodic
changing of high and low pressure zones in the wake region disappears resulting in
breaking large scale vortices. For real world and ocean energy applications including
elements with spherical shapes, data from present work will be very useful to
evaluate, especially for drag and lift forces, flow induced vibrations, pressure
gradients obtained by means of numerical investigations.
Bu çalışmada, bir açık kanal akışının serbest yüzeyine yakın konumlarda akışa yatay olarak yerleş... more Bu çalışmada, bir açık kanal akışının serbest yüzeyine yakın konumlarda akışa yatay olarak yerleştirilen bir
silindirin art izi ile serbest yüzey etkileşimi incelenmiştir. Deneysel çalışma için Selçuk Üniversitesi İleri Ar-Ge
Merkezi’nde bulunan açık su kanalında, Parçacık Görüntüleme Hız Ölçüm (PIV) sistemi kullanılmıştır. Deneyler,
silindirin üst noktası ve serbest yüzey arasındaki mesafe (h) ile silindir çapının (D) oranı olan h/D=0, 0.25, 0.50 ve
1.0 değerlerinde yapılmıştır. Serbest akış hızı (U∞=200mm/s) ve silindir çapı (D=50mm) ile tarif edilen Reynolds
sayısı 10000 olarak seçilmiştir. Froude sayısı su derinliğine bağlı olarak
Fr U ghw =0.095 hesaplanmış olup 1'
den küçük olduğu için serbest yüzey kritik altı akış şartlarındadır. Serbest yüzey ve silindir art izi etkileşimini
incelemek için, zaman ortalaması hesaplanan hız vektörleri, akım çizgileri ve akış doğrultusundaki hız bileşenleri
kullanılmıştır. Serbest yüzey etkisinden dolayı silindirin art izi önemli oranda etkilenmekte, bu bölgedeki akışın enerji
yoğunluğu ve dönüm miktarı değişmektedir. Silindir yüzeye temas ettiğinde, silindirin altında kalan bölgede
sürekliliği sağlamak için akış oldukça hızlanmaktadır. Silindir daldırma miktarı arttıkça, özellikle silindirin üst
kısmından geçen akıştan kaynaklanan momentum transferi nedeniyle art izi bir miktar kısalmaktadır. Serbest yüzeyin
sönümleme etkisi art izini etkilemekte ve silindir serbest yüzeyden uzaklaştıkça yüzey etkisi azalmaktadır ve ayrılmış
akış yüzeyle birleşmemektedir. Daldırma oranı h/D=1.0 oranında ise serbest yüzeyin etkisi ihmal edilebilir mertebede
olmakta ve zaman ortalaması alınmış akışın art izi yapısı simetriğe yaklaşmaktadır.
Experimental results of interaction between fluid free surface and wake region of a horizontal smooth
cylinder beneath the free surface region in an open water channel flow are presented. Experiments were performed in
a large-scale open water channel at Selcuk University Advanced Research Center via Particle Image Velocimetry
(PIV) system. The experiments were carried out for the different cylinder locations at different depth ratios of h/D=
0, 0.25. 0.50 and 1. Here, h is the gap between the top point of the cylinder and free surface, and D is the diameter of
the cylinder. During the experiments, the Reynolds number based on the cylinder diameter (D=50mm) and free
stream velocity (U∞=200mm/s) was taken as Re=10000. The Froude number based on the water depth (hw) was
Fr U ghw =0.095 depending on the free-stream velocity, which was subcritical flow region owing to the
Froude number less than 1. Time-averaged velocity vector field, streamline topology and streamwise velocity
components were used in order to explain flow structure between the free surface and the cylinder wake region. Due
to the effect of free surface, the wake region of the cylinder is significantly affected so that energy intensity and
recirculation length are changed. When upper side of the cylinder is contacted to free surface, velocity flow in the
bottom side of the cylinder is accelerated due to the energy conversion and blockage effect. As the submerging ratio
increases, the wake region of the cylinder becomes shorter due to the momentum transfer from the upper side of the
cylinder. By increasing the submerging ratio, the effect of the free surface became less and the separated flow from
the periphery of the cylinder was not reattached to the free surface. It is observed that the effect of the free surface on
flow structure is negligible at submerging ratio of h/D=1.0 and time averaged wake region structure become nearly
symmetric.
Akışkan cisim etkileşimi sonucu oluşan akış yapısını incelemek ve etkili açıklık oranını belirlem... more Akışkan cisim etkileşimi sonucu oluşan akış yapısını incelemek ve etkili açıklık oranını belirlemek amacıyla bu
çalışmada, art arda yerleştirilmiş iki küre ile serbest su yüzeyinin etkileşimi, parçacık görüntülemeli hız ölçme
yöntemi (PIV) ile kürelerin değişik daldırma oranlarında ve farklı açıklık oranlarında araştırılmıştır. Deneyler,
kürelerin serbest yüzeyden itibaren daldırma oranının 0.25≤h/D≤2.0 aralığında ve iki kürenin birbirine temas ettiği
durumdan aralarındaki açıklığın 1.0≤G/D≤2.5 aralığında değiştiği ve küre çapına göre tarif edilen Reynolds sayısının
5000 değeri için yapılmıştır. Elde edilen sonuçlar anlık girdap eş düzey eğrileri, akım çizgileri, akım yönündeki hız
değerleri ve çalkantı hızlarının değişimleri olarak sunulmuştur. Serbest yüzeyin akış yapısına etkisinin daldırma
oranının h/D=1.0 olduğu duruma kadar devam ettiği görülmüştür. Daldırma oranı arttıkça, kürelerin açıklık oranının
G/D=2.50 olduğu durumda ön kısımda bulunan kürenin art izindeki akış yapısı simetrik bir hal almaktadır. Açıklık
oranı G/D=1.0 olduğu durum haricinde, ön tarafta bulunan kürelerin tüm açıklık oranlarında art izi bölgesinde iki adet
odak noktasının oluştuğu sadece h/D=2.0 daldırma oranında elde edilmiştir. Farklı daldırma oranlarında küreler
etrafından ayrılan akış, serbest yüzeyle birleşmeden serbest akım hızıyla sönümlenerek yoluna devam etmektedir.
Kürenin alt ve üst kısmından kopan negatif ve pozitif girdaplar ile küre etrafındaki akış yapısının türbülanslı ve çok
karmaşık olduğu anlık girdap eş düzey eğrilerinden tespit edilmiştir. İki küre arasındaki mesafe ve kürelerin daldırma
oranları arttıkça, küreler çevresindeki akış yapısının birbirinden bağımsız yerleştirilmiş iki kürede oluşan art izine
benzemektedir.
In this study, in order to investigate the flow structure formed by fluid-body interaction and to determine
effective spacing ratio, interaction between free water surface and tandem arranged of the two spheres was
investigated via Particle Image Velocimetry method with various submerging ratios and at different spacing ratios of
spheres. Experiments were carried out with submerging ratios of 0.25≤h/D≤2.0 and spacing ratios of 1.0≤G/D≤2.5,
and Reynolds number value, which is defined based on the sphere diameter, taken as 5000. The obtained results were
presented as instantaneous vorticity, time-averaged streamline patterns, streamwise velocity components and
streamwise velocity fluctuations. It is observed that the effect of free surface on flow structure until submerging ratio
of h/D=1.0. In the case of spacing ratio for 2.50, as submerging ratio increases, the flow structure at the wake region
of sphere at front becomes symmetrical. For h/D=2.0, at the wake region of sphere at front two foci points formed for
all spacing ratios apart from G/D=1.0. The flow separated from the periphery of the spheres continued downstream as
suppressed without reattaching to the free surface for different submerging ratios. From the instantaneous vorticity
contour maps comprised data from vortices shed from upper and down parts of the sphere, it was realized that flow
structure is very turbulent and chaotic. As the distance between the two spheres and the submerging ratio get bigger,
flow around spheres gets similar to the flow around two independent spheres in different flow mediums.
Aktif güvenlik sistemleri arasında yerini alan klima sistemi, günümüz taşıtlarında standart bir d... more Aktif güvenlik sistemleri arasında yerini alan klima sistemi, günümüz taşıtlarında standart bir donanım olarak
bulunmaktadır. Klima sistemi, konvensiyonel ve hibrit taşıtların yakıt ekonomisini ve emisyonlarını etkileyen en
önemli yüklerdendir. Bu çalışma da, taşıt klima sistemi bir minibüs üzerine kurulmuş, klima performansını belirlemek
amacıyla sıcaklık, basınç ve nem sensörleri, debi ölçer ve güç ölçer cihazları ile donatılan sistem yaz aylarında
dinamik çevre şartlarında test edilmiştir. Çalışmada, evaporatör üzerinden geçen hava debisinin sabit olması
durumunda (kanal içerisindeki ortalama hızının 8 m/s değeri için), kompresör hızının (devrinin) değişiminin klima
performansına etkisi araştırılmıştır. Elde edilen deneysel sonuçlardan sistemin Konya ilinde çalıştırılması ile Soğutma
Tesir Katsayısının (STK’nın) artan kompresör devri (1000 d/dk dan 3000d/dk) ile STK’nın 3.85’den 2.12’e kadar
düşerek azaldığı ve minimum STK’nın yaklaşık 2 olduğu görülmüştür. Performans deneylerinden elde edilen
sonuçların zamana bağlı değişimleri detaylı analiz edilerek, yorumlanmıştır.
Air conditioner system that has ranked among active safety systems is found in today’s vehicle as a
standard hardware. Power requirement of air conditioner is one of the most important loads on the vehicle engine,
which affects fuel economy and exhaust emissions of conventional and hybrid vehicles. Air conditioner system was
installed on a minibus in this study and the experimental system equipped with temperature, pressure and humidity
sensors, flow meter and power meter was tested at dynamic environmental conditions in order to determine air
conditioner performance for a parked condition. A constant capacity compressor, an expansion valve with external
compensation and R134a refrigerant were used in air conditioner. Effect of the compressor speed on air conditioner
performance was investigated when the air flow speed through evaporator is fixed (for the 8 m/s value of average air
speed in the channel). It was seen from the experimental results that Coefficient of Performance (COP) of the system
was decreased from 3.85 to 2.04 in case of the system operation in Konya when the compressor speed is risen from
1000 rpm to 3000 rpm and the minimum COP was approximately 2. Time dependent variation of the results from the
performance experiments were analyzed and interpreted.
Bu çalışmada, düz bir levha üzerindeki hidrodinamik olarak gelişmiş sınır tabaka içerisine farklı... more Bu çalışmada, düz bir levha üzerindeki hidrodinamik olarak gelişmiş sınır tabaka içerisine farklı yüksekliklerde
yerleştirilen pürüzsüz art arda iki kürenin art izi bölgesinde oluşan akış yapısı Parçacık Görüntülemeli Hız Ölçme
(PIV) tekniği ile deneysel olarak araştırılmıştır. Su kanalında yapılan deneylerde, serbest akım hızına ve küre çapına
göre tanımlı Reynolds sayısı Re=5000’dir. Açık kanal hız değeri (0.118 m/s) sınır tabaka akışına neden olan levhanın
yaklaşık 63 mm üzerinde serbest akım değerlerine %1’den daha küçük bir farkla ulaştığı belirlendiği için,
hidrodinamik sınır tabaka kalınlığı 63 mm olarak saptanmıştır. Sınır tabaka akışı etkisinde olan konuma art arda
yerleştirilen pürüzsüz küreler etrafındaki akış yapısının ortalama akım çizgileri, akım yönündeki hız çalkantıları ve
Reynolds gerilmeleri küre çapı (D) ile küre-levha yüzeyi arasındaki boşluk (H) oranının 0≤H/D≤1.5 olduğu aralıkta
akış fiziğinde oluşan değişimleri belirlenmiştir. Küreler düz levhaya yakın konumlarında, levha ile kürelerin alt tarafı
arasında oluşan jet formundaki akış hem iki küre arasındaki bölgeyi etkilemekte, hem de aşağı akım yönündeki
kürelerin art izi bölgelerine enerji vererek akışın hareketliliğini arttırmaktadır. Bu karışım ısı transferi uygulamaları
açısından önemlidir. Küreler levha yüzeyinden uzaklaştıkça sınır tabaka etkisi azalmakta ancak iki küre arasındaki
açıklığın (G) küçük değerlerinde art izi bölgesinde dönümlü akış bölgesi küre levha arasındaki mesafeden bağımsız
olarak önemli oranda etkilenmektedir.
In this study, flow structure around two smooth spheres arranged tandem inside different elevations of a
hydrodynamically developed boundary layer over a flat plate is investigated experimentally via Particle Image
Velocimetry (PIV) technique. Reynolds number taken as 5000 based on the free-stream velocity and sphere diameter.
Hydrodynamic boundary layer thickness was determined as 63 mm since the open channel velocity (0.118 m/s) over
the flat plate causes boundary layer flow reaches to free stream velocity with a difference less than 1% of free stream
velocity. The time-averaged streamline patterns, streamwise velocity fluctuations and Reynolds stress correlations of
flow structure around tandem arranged two smooth spheres placed under boundary layer effect were investigated in
terms of sphere diameter (D) and sphere-plate gap (G) ratio changes between 0≤H/D≤1.5. While the spheres are in the
positions close to flat plate, the jet flow between flat plate and sphere creates flow mixing by energizing the flow field
between two spheres and the wake region of the sphere in the downstream direction. The mixing is important in terms
of heat transfer applications. As the spheres moves upward from the flat plate, the effect of the boundary layer
decreased, however, the recirculation region in the wake regions of the two spheres are significantly affected for the
smaller gaps between the spheres (G) as dependent of the distance between the sphere and plate.
Transfer edilen ısı miktarını arttırmak ve oluşan basınç düşüşünü kabul edilebilir sınırlar içeri... more Transfer edilen ısı miktarını arttırmak ve oluşan basınç düşüşünü kabul edilebilir sınırlar içerisinde tutmak için,
birçok ısı değiştiricide kullanım şartlarına bağlı olarak farklı geometrilere sahip kanatçık olarak adlandırılan
genişletilmiş ısı transfer yüzeyleri kullanılmaktadır. Isı değiştirici kapasitesinin hesaplanabilmesi için ısı taşınım
katsayısının bilinmesi gerekir. Bununla beraber aynı akış şartlarında ve sıcaklık farkında farklı kanatlar ve geometriler
ile ısı taşınım katsayısı farklılık göstermektedir. Kanat geometrisine ve akış özelliklerine bağlı bu katsayısının
belirlenmesi için literatürde çeşitli deneysel ve sayısal yöntemler kullanılmaktadır. Deneysel yöntemlerden biri olan
Wilson Çizim tekniği, uygun deneysel sonuçlar kullanılarak belirli bir ısı değiştirici geometrisi için ısı taşınım
katsayılarının hesaplanmasına yönelik deneysel eşitlik üretmeye yarayan bir metottur. Wilson Tekniği özünde transfer
edilen ısı ile sıcaklık farkı arasında, akış ve akışkan özelliklerini de dikkate alarak bir bağıntı elde etmeye yarayan ve
deneysel ölçüme dayanan bir doğrusal eğri bulma yöntemidir. Böylece ısı taşınım katsayıları elde edilebilmekte ve
boyutsuz sayılar ile ısı transferine etki eden birçok parametre tek bir grafikle ifade edilebilmektedir.
Bu çalışmada, ticari olarak üretilen ara soğutucu amaçlı kullanılan çapraz akışlı, tek geçişli kompakt bir ısı
değiştiricinin ısıl performansını belirlemek için farklı şartlarda deneyler yapılmıştır. Çalışmada ayrıca, bahsedilen ısı
değiştirici için ε-NTU yöntemiyle bulunan toplam ısı transfer katsayısı ve Wilson Çizim Tekniği kullanılarak ısı
taşınım katsayılarının bulunması incelenmiştir. Ara soğutucudan geçen sıcak akışkanın ısı değiştiriciye giriş sıcaklığı
60, 80, 100 ve 120 oC olarak ayarlanmıştır. Seçilen ara soğutucu için dolgu havası tarafında Colburn j katsayısı
0,002866-0,003592 arasında değişmiştir. Elde edilen değerler üç farklı literatür verisi ile karşılaştırıldığında bir tanesi
ile ±%10 mertebesinde uyumlu olduğu bulunmuştur.
Fins as enhanced heat transfer surfaces with different geometries for various operational conditions are used
in a vast variety of heat exchangers in order to improve heat transfer amount and keep the pressure drop in allowable
limits. To calculate the heat transfer capacity of a heat exchanger, heat convection coefficients of the fluid streams
have to be known. Nonetheless, heat convection coefficients get different values for different fin geometries at same
flow conditions and temperature differences. Various experimental and numerical methods are utilized in the literature
for obtaining heat convection coefficients dependent to fin geometry and flow properties. As one of the experimental
methods, Wilson plot technique serves for empirical equation derivation in order to calculate heat convection
coefficients for certain heat exchanger geometry by using proper experimental results. In its essence, Wilson plot
technique is a linear curve fitting method dependent to experimental results that is useful for obtaining a correlation
between transferred heat and temperature difference considering flow and fluid properties. In this way heat convection
coefficients can be obtained and numerous factors affecting the heat transfer can be represented by few dimensionless
numbers in a single graphic.
In the present study, experiments were conducted for different experimental parameters in order to determine thermal
performance of a cross flow single pass compact heat exchanger which is used as a commercial intercooler. Additionally, the calculation of the heat convection coefficients using Wilson plot technique with overall heat transfer
coefficient obtained by means of ε-NTU method for the aforementioned heat exchanger is also discussed in the study.
The entrance temperature of the charge air to the intercooler was arranged as 60, 80,100 and 120 oC. Colburn j factor
changed between 0,002866-0,003592 for the selected intercooler. It was found that, obtained results are in consistency
with one of the three literature data at a ratio of ±10%.
Silindir birçok endüstriyel ve ticari uygulamada çeşitli formlarda kendine yer bulan temel bir ge... more Silindir birçok endüstriyel ve ticari uygulamada çeşitli formlarda kendine yer bulan temel bir geometridir.
Dolayısıyla silindir geometrilerine akışların hidrodinamik etkileri uygulamaya bağlı farklılıklar göstermektedir ve bu
etkilerin araştırılması birçok uygulamada tasarım, iyileştirme ve geliştirme faaliyetlerine katkıda bulunacaktır.
Yapılan çalışmada türbülanslı bir sınır tabaka içerisine düz pürüzsüz levha yüzeyinden farklı yüksekliklerde akışa dik
doğrultuda yatay olarak yerleştirilen silindir geometrisi etrafında oluşan akış yapısı ve buna bağlı hidrodinamik etkiler
Parçacık GörüntülemeLİ Hız Ölçme Yöntemi (PIV) ile incelenmiştir. Deneyler Selçuk Üniversitesi İleri Ar-Ge
Merkezi’nde bulunan PIV ölçme sistemi ve açık su kanalında yapılmıştır. Deneylerde kullanılan akrilik silindirin çapı
50 mm seçilmiştir ve silindir çapına bağlı Reynolds sayısı 10,000’dir. Levha yüzeyi ile silindirin alt noktası
arasındaki boşluk, silindir çapının 0, 0.25, 0.50, ve 1 katı olacak şekilde deneyler tekrarlanmıştır. Silindirin üzerine
yerleştirildiği düz plaka üzerinde türbülans sınır tabaka elde edebilmek için plakanın hücum kenarına yakın bölgede
türbülans oluşturucu bir çubuk (trip wire) kullanılmıştır. Sınır tabaka etkisi nedeniyle silindirin düz levhaya temas
ettiği durumda silindir yüzeyinde akış ayrılma noktasının arka noktalara doğru kaydığı ve art izinin literatürde iyi
bilinen laminer sınır tabaka etkisine göre daha dar olduğu gözlemlenmiştir. Silindir levha yüzeyinden uzaklaştıkça
silindirin alt kısmında ortaya çıkan jet akışı art izi bölgesini yukarı yönlendirerek uzatmaktadır. Levha yüzeyinde
oluşan sınır tabaka ile silindir yüzeyindeki akış ayrılması ve silindir ile levha arasındaki jet akış birbirini etkilemekte
ve karmaşık üç boyutlu düzensiz dönümlü bir art izine neden olmaktadır. Levha yüzeyinde bu şekilde oluşan şiddetli
akış, uygulamada aşınmalara, istenmeyen ses ve gürültülere neden olabilmektedir. Bu nedenle bu etkileşimleri
azaltmak amacıyla silindir çevresinde oluşan akış yapısını kontrol edici yöntemler geliştirilmesi gerekir.
Cylinder is a basic geometry that has applications with various forms in a lot of industrial and commercial
areas. Therefore hydraulic effects of fluids on cylinder geometries exhibit different characteristics depending on the
application and investigation for these different effects will contribute to design, improvement and development tasks
in a lot of applications. In the conducted study, flow structure around cylinder geometry placed horizontally
perpendicular to the flow direction at different elevations from the floor of flat smooth plate in a turbulent boundary
layer and hydrodynamic effects dependent to these were investigated via Particle Image Velocimetry (PIV).
Experiments were performed in an open water channel and PIV system of Selcuk University Advanced R&D center.
Plexiglas cylinder used in experiments has a diameter of 50 mm and Reynolds number based on the cylinder diameter
was 10,000. Experiments were repeated for each position at which the distance between the bottom point of the
cylinder and the flat plate were 0, 0.25, 0.50 and 1 times of the cylinder diameter. A tripwire was utilized in order to
stimulate a turbulent boundary layer on the flat plate and tripwire was placed near to a location at the leading edge of
the flat plate. It was observed that the separation point from the surface of the cylinder moved towards downstream
and delayed and wake region of the cylinder was narrower at the lower side of the cylinder comparing to upper side
because of velocity gradient of the boundary layer. Also jet flow occurred between down part of the cylinder and the
flat plate lead wake region to upward direction as the gap increased due to momentum transfer. Boundary layer over
the flat plate, flow separation over the cylinder and jet flow between the cylinder and the flat plate affect each other
and cause to a complex three dimensional unsteady wake comprising vortices. This kind of flow with high intensity
causes wear, unwanted noise and vibrations in application. Hence methods that can control the flow structure around
the cylinder should be developed in order to reduce these kinds of interaction effects.
Flow structure around geometries similar to
circular cylindrical geometries in various industrial... more Flow structure around geometries similar to
circular cylindrical geometries in various industrial and daily life applications must be known in respect of energy efficiency and stability for different flow conditions. In this sense, flow structures in the wake of a circular cylinder located in a boundary layer flow and a flow region near to free flow surface were examined by means of PIV system in an open water channel. Circular cylinder was parallel to boundary layer plate and perpendicular to flow direction. Experiments were conducted primarily in a region near to the free surface of the flow and then in the boundary layer flow at various locations of the cylinder diameter (D) ratios of contacting case, 0.00D, 0.25D, 0.50D and 1.0D. Cylinder diameter was 50 mm and Reynolds number calculated according to this diameter was selected 5000.
For the experiments, Stereo Particle Image Velocimetry Setup in Selcuk University Mechanical Engineering Department
Hydraulic Laboratory was utilized. Results obtained as the
consequence of investigation of flow around circular cylinder at different flow conditions are presented in the form of time
averaged streamwise velocity component contours and timeaveraged vorticity contours. It is shown that wake structures of circular cylinder immersed in a boundary layer flow exhibited considerably different characteristics compared to the flow structures obtained at flow region near to free surface of the flow.
In this study, a stereo PIV system was utilized in order to measure flow structures in the wake r... more In this study, a stereo PIV system was utilized in order to measure flow structures in the wake region of
various non-circular cylinders located in a shallow water flow. Free Stream flow velocity of the shallow water was
adjusted to obtain the Reynolds numbers i.e. 5000 and 10000 based on the characteristic length of each cylinder. A
circular cylinder was also tested in order to establish results for comparison of ellipse, triangle, rectangle and square
cross-section cylinders. Measurement plane was parallel to the boundary layer plate and at the middle point of the
immersed parts of cylinders. Interactions between stream free surface and boundary layer flow, and non-circular
cylinder geometries were evaluated in respect of physics of flow phenomenon. Ellipse and rectangular cylinders form
very small wake regions and vortex streets yield narrower wake structure when compared to the square and triangular
cylinders. In triangular cylinder case, two different placements that were sharp edge faced towards upstream and
sharp edge directed to downstream were done. It was demonstrated that wider wake region for the sharp-edge towards
the downstream case was occurred while it was nearly half of the wake region of the sharp-edge directed to
downstream case. Quantitative results are also presented in the paper by means of color scales and contour lines to
make more distinctive comparison. Results can be used in evaluation of various construction and design studies as
well as computational fluid dynamics applications according to Reynolds Number analogy.
In this study, flow characteristics past a sphere and dual spheres in side-by-side, staggered at ... more In this study, flow characteristics past a sphere and dual spheres in side-by-side, staggered at an angle of 30o
and in-lined arrangements were experimentally investigated. The experiments were conducted employing a Particle
Image Velocimetry (PIV) system and Rhodamine 6G dye method in a water channel at Re=5000. A peculiar geometry
of sphere/Spheres orients the instantaneous flow characteristics around sphere/spheres to be profoundly three
dimensional as well as unsteady in the wake region. It was demonstrated that all of the arrangements developed a very
chaotic structure in the wake region. In addition, time-averaged flow patterns such as streamline topology, velocity
components, rms velocities in x and y directions were fairly symmetrical with respect to the sphere equator line. Dual
sphere experiments were performed with three altered gap ratios (G/D) of spheres, for example, G/D=1.0, 1.5 and 2.0.
Here, G is the length between the focal points of the spheres and D is the sphere diameter. In comparison to a sphere
case, at G/D=1.0, appearances of wake of dual spheres are identical to a single sphere case but the wake expands to a
larger size. A jet flow at G/D=1.5 occurs between the spheres for three different arrangements. For G/D=2.0, the wake
for each sphere becomes a separated region and the effect of jet like flow disappears more or less completely. The
results obtained in this study can be a fruitful source for developing and validation of new codes both in scientific and
commercial manner.
Two independent spheres were placed in a side by side arrangement and flow structure in the wake
... more Two independent spheres were placed in a side by side arrangement and flow structure in the wake
region of the spheres was investigated with a Particle Image Velocimetry (PIV) system when the spheres were
in a boundary layer over a flat plate as a special case. Reynolds number was 5000 based on the sphere diameter
which was 42.5 mm. Boundary layer was tripped 8mm away from the leading edge of the flat plate with a 5
mm trip wire. The thickness of the hydrodynamically developed boundary layer was determined as 63mm
which was larger than the sphere diameter of D=42.5mm. Wake region of the spheres was examined from point
of flow physics for the different sphere locations in the ranges of 0G/D 1.5 and 0S/D 1.5 where G and S
were the distance between the spheres and the distance between the bottom point of the spheres and the flat
plate surface, respectively. Depending on the different sphere locations, instantaneous and time averaged
vorticity data, scalar values of time-averaged velocity components and their root mean square (rms) values and
time averaged vorticity data are presented in the study for the evaluation of wake region of the spheres. It is
demonstrated that the gap between the two spheres and the interaction between the gap and the boundary layer
greatly affects flow pattern, especially when spheres are located near to the flat plate surface, i.e. S/D=0.1 for
0G/D 1.5. Different distances between the spheres resulted in various flow patterns as the spheres were
approached to the flat plate. The distance S/D=0.1 for all gap values has the strongest effect on the wake
structures. Beyond G/D=1.0, the sphere wakes tend to be similar to single sphere case. The instantaneous
vorticity fields of the side by side arrangements comprised wavy structures in higher level comparing to an
individual sphere case. The gap flow intensifies the occurrence of small scale eddies in the wake region. The
submersion rate of the spheres actually determines the characteristics of the wake region and is affected from
boundary layer flow in a gradually decreasing manner.
In this study, an absorption system using ammonia-water (NH 3 -H 2 O) solution has been theoretic... more In this study, an absorption system using ammonia-water (NH 3 -H 2 O) solution has been theoretically examined in order to meet the cooling need of a detached building having 150 m 2 floor area for Antalya, Mersin and Mugla provinces in Turkey. Hourly dynamic cooling load capacities of the building were determined by using Radiant Time Series (RTS) method in the chosen cities. For the analysis, hourly average meteorological data such as atmospheric air temperature and solar radiation belonging to the years 1998-2008 are used for performance prediction of the proposed system. Thermodynamic relations for each component of absorption cooling system is explained and coefficients of performance of the system are calculated. The maximum daily total radiation data were calculated as 7173 W/m 2 day on July 15, 7277 W/m 2 day on July 19 and 7231 W/m 2 day on July 19 for Mersin, Antalya and Mugla, respectively on the 23° toward to south oriented panels from horizontal surface. The generator operating temperatures are considered between 90-130°C and the best result for 110°C is found the optimum degree for maximum coefficient of performance (COP) values at the highest solar radiation occurred time during the considered days for each province. The COP values varies between 0.521 and 0.530 for the provinces. In addition, absorber and condenser capacities and thermal efficiency for the absorption cooling system were calculated. The necessary evacuated tube collector area for the different provinces were found in the range of 45 m 2 to 47 m 2 . It is shown that although the initial investment cost is higher for the proposed absorption cooling system, it is economically feasible because of its lower annual operation costs and can successfully be operated for the considered provinces.
EPJ Web of Conferences, 2012
In this study, instantaneous and time-averaged flow structures downstream of the sharp-edged sing... more In this study, instantaneous and time-averaged flow structures downstream of the sharp-edged single and two and three side-by-side square cylinders (SCs) immersed in a uniform open channel water flow were studied by a technique of particle image velocimetry (PIV). Experimental results of wake flow structures were presented for gap ratios (G/D) in the range of 1.0G/D3.0 for Reynolds number values of 1050, 2450 and 3400. Flow structures depending on the square cylinder (SC) configurations and Reynolds number were discussed. It has been found that the development of the vortex shedding as well as the flow structure were substantially altered for side-by-side SCs comparing to the single SC. Asymmetrical and biased wake structures were observed because of the jetlike flow between the SCs for two SCs cases for the gap ratio less than 2.0. Depending on the gap spacing between the SCs, the interaction results of timeaveraged vorticity, velocity vector field, Reynolds stress correlations ! f 2 U v' u' and streamline patterns in the wake region form a distinguished flow structure. Strouhal numbers for the single square cylinder for 1050Re3400 are found in the range of 0.12-0.13. The present results have supported the previous works by providing detailed quantitative experimental information with PIV in the wake region of the SC and might be helpful for validation of numerical studies and designers.
Journal of Mechanical Science and Technology, 2013
Large eddy simulation, using a dynamic Smagorinsky sub-grid scale, is used for the prediction of ... more Large eddy simulation, using a dynamic Smagorinsky sub-grid scale, is used for the prediction of flow structures around two identical spheres fixed side-by-side at a subcritical flow regime with the Reynolds number equal to 5,000. The QUICK discretization method is applied to discretize the convection terms of the Navier-Stokes equation by means of the finite volume approach. This work focuses mainly on the wake structures downstream of the two interactive spheres located at three various dimensionless separation distances between spheres such as G/D = 1.50, 2.00, and 3.00. The obtained results revealed that the interaction between wakes affects the flow structures downstream of spheres. The rate of this interaction is strongly altered as a function of separation distance. On the other hand, some flow data such as mean drag and mean lift coefficients are affected due to the wake interactions. Finally, examination of the Reynolds stress variation along the different lateral axis, L/D, revealed that the nozzle effect does not play a significant role on the turbulence characteristics beyond the G/D = 3.00.
International Journal of Heat and Fluid Flow, 2011
An experimental investigation of flow structures downstream of a circular cylinder and sphere imm... more An experimental investigation of flow structures downstream of a circular cylinder and sphere immersed in a free-stream flow is performed for Re = 5000 and 10,000 using qualitative and quantitative flow visualization techniques. The obtained results are presented in terms of time-averaged velocity vectors, patterns of streamlines, vorticity, Reynolds stress correlations and turbulent kinetic energy distributions. Flow data reveal that the size of wake flow region, the location of singular and double points, the peak values of turbulence quantities, such as Reynolds stress correlations, vorticity fluctuations and turbulent kinetic energy vary as a function of models' geometry and Reynolds Numbers. The concentration of small scale vortices is more dominant in the wake of the sphere than that of the cylinder. The maximum value of turbulent kinetic energy (TKE) occurs close to the saddle point for the cylinder case while two maximum values of TKE occur along shear layers for the sphere one because of the 3-D flow behavior.
International Journal of Computational Fluid Dynamics, 2011
A numerical investigation of flow around a sphere is performed and compared with previous studies... more A numerical investigation of flow around a sphere is performed and compared with previous studies. Here, a second-order accurate, finite volume method is used in order to predict the instantaneous and time-averaged flow characteristics using large eddy simulation (LES) on the multi-block grid system. Namely, the objectives of this article are: (i) the presentation of flow structures in the wake region downstream of the sphere with a wide variety of flow properties such as the distribution of velocity vectors, patterns of streamlines, Reynolds stress correlations, root mean square of velocity components and other time-averaged flow data in order to reveal the vortical flow structures in detail and (ii) to demonstrate the abilities of computational methods in simulation of vortical flow data. Finally, it has been concluded that there are good agreements between the experimental results and numerical predictions.
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Papers by Muammer Ozgoren
debimetreler kullanılmaktadır. Bu cihazlar bilgi maliyeti, navlun, vergiler gibi maliyetlerden dolayı
kullanıcı için pahalı bir çözümdür. Ayrıca genellikle stok tutulmadığı için kullanıcının 4 ila 8 hafta gibi
uzun süreler beklemesi gerekmektedir. Bununla beraber gelen ürünlerin kullanımında, bir arıza
durumunda müdahalede ve kalibrasyon konularında sınırlı teknik destek söz konusudur.
Bu çalışmada ithal debimetrelere alternatif olarak geleneksel ventüri tüpü ve bir elektronik veri toplama
düzeneği kullanarak debi ölçümü ve sonuçları incelenmiştir. Biri sıvı diğeri ise gaz olmak üzere iki
farklı akışkanın debilerinin ölçülmesi için iki farklı ventüri tüpü hazırlanmıştır ve aynı elektronik veri
toplama düzeneğinde ölçümler kaydedilerek hesaplamalar yapılmıştır. Akışkanlardan gaz olan hava,
sıvı olan ise ST42 numaralı endüstriyel yağdır. Yağ akışkan, ölçümler sırasında 100 oC sıcaklığa
kadar ısıtılmıştır. Çalışma sonuçlarına göre ventüri tüpünün dinamik debi ölçümünde dahi etkin
biçimde kullanılabileceği gösterilmiştir.
seçiminde önemli kriterler ısı transferi ve basınç düşüşü performansı, maliyet, kompaktlık ve etkenlik
olarak sıralanabilir. Bununla birlikte son yıllarda enerji kullanımına yönelik yapılan çalışmalar farklı
sistemlerdeki enerji kullanılabilirliğinin yani ekserjinin de değerlendirilmesi gerektiğini ortaya
koymaktadır. Aynı zamanda ikinci yasa yaklaşımı, bir optimizasyon problemi olan ısı değiştirici
tasarımında da yer almaktadır.
Yapılan çalışmada 650-670 kompaktlık oranına sahip üç farklı tipteki ısı değiştirici 0.027-0.16 ısıl
kapasite oranlarında deneysel olarak incelenmiştir. İnceleme sonuçları kullanılarak ısı değiştiricilerinde
gerçekleşen ekserji yıkımı hesaplanmıştır. Ekserji yıkım değerleri açısından ısı değiştiricileri
karşılaştırılmıştır. Karşılaştırma sırasında ısı değiştiricilerin ısı transferi yüzey alanlarının dağılımı,
tersinmezlik değerleri, tersinmezliğin sıcaklık ve basınç bileşenleri ve ekserji verimleri kullanılmıştır.
Heat transfer and pressure drop performance, cost, compactness and effectiveness can be listed as
important criteria for selection of widely utilized compact heat exchangers in buildings and a lot of
other industrial areas. Nevertheless, recent studies intended for energy usage presents that usability
of the energy, namely exergy, should be evaluated for various systems. The second law approach is
also used for heat exchanger design which is an optimization problem.
In this work, three different type heat exchangers having 650-670 compactness ratios were
experimentally investigated between 0.027-0.16 heat capacity ratios. Exergy destruction occurred in
the heat exchangers were calculated using the investigation results. Distribution of heat transfer
surface area of the heat exchangers, irreversibility rates, temperature and pressure components of the
irreversibility and exergy efficiency were used for comparison.
applications such as bridge legs, electricity production from vortex induced
vibrations, petroleum and natural gas lines, off-shore and on shore structures and
wind turbine bodies. Flow structures around these geometries have important effects
on forces acting upon these geometries. Therefore, performances of industrial
designs can be improved by controlling flow structure.
Experiments were carried out in an open water channel at Mechanical
Engineering Department of Selcuk University. In the present study, flow structure
around a cylinder with circular cross section was investigated via Particle Image
Velocimetry (PIV) technique in uniform flow condition. Thereafter a knitted porous
structure was wrapped around the cylinder in order to apply a passive flow control in
the wake structure of the cylinder. Free stream velocity during the experiments was
arranged as the Reynolds number based on the cylinder diameter of 50mm was
10000. Velocity vector field, streamline topology, streamwise velocity components
and Reynolds stress correlations were used in order to explain flow structure around
the cylinders for the sake of comparison. At the end of the experiments, it was
realized that the porous knitted structure extended the size of wake and elongated
wake length of the cylinder and increased the velocity distributions in the wake
while decreasing the strength. The wake was extended approximately half cylinder
diameter in width and elongated approximately one cylinder diameter in length
when the passive flow control was applied. The size of foci points in the wake of the
cylinder without passive control were evaluated as they were relatively small
comparing to the that of the cylinder with passive control. In the wake of the
cylinder with passive control, a saddle point occurred in the further downstream
comparing to the wake of the cylinder without passive flow control. This study
presents to control the flow around a circular cylinder through the implementation of
artificial surface roughness by a knitted coating around the cylinder, which has a
good agreement from the point of flow physics in the literature. These results will be
useful for industrial applications, ocean engineering and ocean energy production
via various similarity approaches. In the future, the knitted structure forming
circular, diamond or trapeze patterns will be tested.
of basic fluid dynamics research. These basic researches include experimental flow
field measurements and also computational fluid dynamics (CFD) analyses. A
particular part of aforementioned studies focus on ocean structures, particularly used
in energy generation, since they contains various basic geometrical shapes. Results
are often presented flow characteristics as free stream velocity, pressure values and
vibrations, vortex induced vibrations. Time Averaged Particle Image Velocimetry
(PIV) is one of the experimental measurement techniques. This technique comprises
instant and time averaged measurement of a complete flow field in respect of flow
velocity. Instant and time averaged vector field, stream lines, scalar value distributions of velocity fluctuations, Reynolds stress correlations, normalized u and
v velocity components and vorticity can be derived.
In this study, two independent spheres were placed in a turbulent boundary
layer in a 30 degree angled tandem position in order to simulate an ocean bottom
situation and interaction between boundary layer and wake regions of the spheres
were investigated with a PIV setup. Results were presented with visual and scalar
data. Thirty five different angled tandem array sphere positions were investigated
experimentally in boundary layer flow for instantaneous velocity vectors, time
averaged velocity vectors, stream lines, scalar values of velocity components, their
RMS values, Reynolds stress. Boundary layer greatly effects flow pattern, especially
when spheres were located within the boundary layer. Different distances between
the spheres yielded dissimilar results. After a specified height from the surface,
evolution of the flow patterns depended to the gap between spheres were
approximately predictable, which is also an indication to ineffective boundary layer
flow. The instantaneous vorticity fields reveal an unsteady wavy structure of the
sphere wake. The concentration of small scale vortices (eddy) is more dominant in
the wake of the sphere when the gap is initiated. It is demonstrated that the presence
of boundary layer flow over the flat plate generates significant complications into
the wake of the spheres due to non-uniform velocity profile, gap flow between the
bottom section of the spheres and flat plate surface. The non-uniform velocity
profile of the boundary layer flow causes a difference in the celerity of the vortex
shedding from the periphery of the spheres. Owing to the jet flow, the periodic
changing of high and low pressure zones in the wake region disappears resulting in
breaking large scale vortices. For real world and ocean energy applications including
elements with spherical shapes, data from present work will be very useful to
evaluate, especially for drag and lift forces, flow induced vibrations, pressure
gradients obtained by means of numerical investigations.
silindirin art izi ile serbest yüzey etkileşimi incelenmiştir. Deneysel çalışma için Selçuk Üniversitesi İleri Ar-Ge
Merkezi’nde bulunan açık su kanalında, Parçacık Görüntüleme Hız Ölçüm (PIV) sistemi kullanılmıştır. Deneyler,
silindirin üst noktası ve serbest yüzey arasındaki mesafe (h) ile silindir çapının (D) oranı olan h/D=0, 0.25, 0.50 ve
1.0 değerlerinde yapılmıştır. Serbest akış hızı (U∞=200mm/s) ve silindir çapı (D=50mm) ile tarif edilen Reynolds
sayısı 10000 olarak seçilmiştir. Froude sayısı su derinliğine bağlı olarak
Fr U ghw =0.095 hesaplanmış olup 1'
den küçük olduğu için serbest yüzey kritik altı akış şartlarındadır. Serbest yüzey ve silindir art izi etkileşimini
incelemek için, zaman ortalaması hesaplanan hız vektörleri, akım çizgileri ve akış doğrultusundaki hız bileşenleri
kullanılmıştır. Serbest yüzey etkisinden dolayı silindirin art izi önemli oranda etkilenmekte, bu bölgedeki akışın enerji
yoğunluğu ve dönüm miktarı değişmektedir. Silindir yüzeye temas ettiğinde, silindirin altında kalan bölgede
sürekliliği sağlamak için akış oldukça hızlanmaktadır. Silindir daldırma miktarı arttıkça, özellikle silindirin üst
kısmından geçen akıştan kaynaklanan momentum transferi nedeniyle art izi bir miktar kısalmaktadır. Serbest yüzeyin
sönümleme etkisi art izini etkilemekte ve silindir serbest yüzeyden uzaklaştıkça yüzey etkisi azalmaktadır ve ayrılmış
akış yüzeyle birleşmemektedir. Daldırma oranı h/D=1.0 oranında ise serbest yüzeyin etkisi ihmal edilebilir mertebede
olmakta ve zaman ortalaması alınmış akışın art izi yapısı simetriğe yaklaşmaktadır.
Experimental results of interaction between fluid free surface and wake region of a horizontal smooth
cylinder beneath the free surface region in an open water channel flow are presented. Experiments were performed in
a large-scale open water channel at Selcuk University Advanced Research Center via Particle Image Velocimetry
(PIV) system. The experiments were carried out for the different cylinder locations at different depth ratios of h/D=
0, 0.25. 0.50 and 1. Here, h is the gap between the top point of the cylinder and free surface, and D is the diameter of
the cylinder. During the experiments, the Reynolds number based on the cylinder diameter (D=50mm) and free
stream velocity (U∞=200mm/s) was taken as Re=10000. The Froude number based on the water depth (hw) was
Fr U ghw =0.095 depending on the free-stream velocity, which was subcritical flow region owing to the
Froude number less than 1. Time-averaged velocity vector field, streamline topology and streamwise velocity
components were used in order to explain flow structure between the free surface and the cylinder wake region. Due
to the effect of free surface, the wake region of the cylinder is significantly affected so that energy intensity and
recirculation length are changed. When upper side of the cylinder is contacted to free surface, velocity flow in the
bottom side of the cylinder is accelerated due to the energy conversion and blockage effect. As the submerging ratio
increases, the wake region of the cylinder becomes shorter due to the momentum transfer from the upper side of the
cylinder. By increasing the submerging ratio, the effect of the free surface became less and the separated flow from
the periphery of the cylinder was not reattached to the free surface. It is observed that the effect of the free surface on
flow structure is negligible at submerging ratio of h/D=1.0 and time averaged wake region structure become nearly
symmetric.
çalışmada, art arda yerleştirilmiş iki küre ile serbest su yüzeyinin etkileşimi, parçacık görüntülemeli hız ölçme
yöntemi (PIV) ile kürelerin değişik daldırma oranlarında ve farklı açıklık oranlarında araştırılmıştır. Deneyler,
kürelerin serbest yüzeyden itibaren daldırma oranının 0.25≤h/D≤2.0 aralığında ve iki kürenin birbirine temas ettiği
durumdan aralarındaki açıklığın 1.0≤G/D≤2.5 aralığında değiştiği ve küre çapına göre tarif edilen Reynolds sayısının
5000 değeri için yapılmıştır. Elde edilen sonuçlar anlık girdap eş düzey eğrileri, akım çizgileri, akım yönündeki hız
değerleri ve çalkantı hızlarının değişimleri olarak sunulmuştur. Serbest yüzeyin akış yapısına etkisinin daldırma
oranının h/D=1.0 olduğu duruma kadar devam ettiği görülmüştür. Daldırma oranı arttıkça, kürelerin açıklık oranının
G/D=2.50 olduğu durumda ön kısımda bulunan kürenin art izindeki akış yapısı simetrik bir hal almaktadır. Açıklık
oranı G/D=1.0 olduğu durum haricinde, ön tarafta bulunan kürelerin tüm açıklık oranlarında art izi bölgesinde iki adet
odak noktasının oluştuğu sadece h/D=2.0 daldırma oranında elde edilmiştir. Farklı daldırma oranlarında küreler
etrafından ayrılan akış, serbest yüzeyle birleşmeden serbest akım hızıyla sönümlenerek yoluna devam etmektedir.
Kürenin alt ve üst kısmından kopan negatif ve pozitif girdaplar ile küre etrafındaki akış yapısının türbülanslı ve çok
karmaşık olduğu anlık girdap eş düzey eğrilerinden tespit edilmiştir. İki küre arasındaki mesafe ve kürelerin daldırma
oranları arttıkça, küreler çevresindeki akış yapısının birbirinden bağımsız yerleştirilmiş iki kürede oluşan art izine
benzemektedir.
In this study, in order to investigate the flow structure formed by fluid-body interaction and to determine
effective spacing ratio, interaction between free water surface and tandem arranged of the two spheres was
investigated via Particle Image Velocimetry method with various submerging ratios and at different spacing ratios of
spheres. Experiments were carried out with submerging ratios of 0.25≤h/D≤2.0 and spacing ratios of 1.0≤G/D≤2.5,
and Reynolds number value, which is defined based on the sphere diameter, taken as 5000. The obtained results were
presented as instantaneous vorticity, time-averaged streamline patterns, streamwise velocity components and
streamwise velocity fluctuations. It is observed that the effect of free surface on flow structure until submerging ratio
of h/D=1.0. In the case of spacing ratio for 2.50, as submerging ratio increases, the flow structure at the wake region
of sphere at front becomes symmetrical. For h/D=2.0, at the wake region of sphere at front two foci points formed for
all spacing ratios apart from G/D=1.0. The flow separated from the periphery of the spheres continued downstream as
suppressed without reattaching to the free surface for different submerging ratios. From the instantaneous vorticity
contour maps comprised data from vortices shed from upper and down parts of the sphere, it was realized that flow
structure is very turbulent and chaotic. As the distance between the two spheres and the submerging ratio get bigger,
flow around spheres gets similar to the flow around two independent spheres in different flow mediums.
bulunmaktadır. Klima sistemi, konvensiyonel ve hibrit taşıtların yakıt ekonomisini ve emisyonlarını etkileyen en
önemli yüklerdendir. Bu çalışma da, taşıt klima sistemi bir minibüs üzerine kurulmuş, klima performansını belirlemek
amacıyla sıcaklık, basınç ve nem sensörleri, debi ölçer ve güç ölçer cihazları ile donatılan sistem yaz aylarında
dinamik çevre şartlarında test edilmiştir. Çalışmada, evaporatör üzerinden geçen hava debisinin sabit olması
durumunda (kanal içerisindeki ortalama hızının 8 m/s değeri için), kompresör hızının (devrinin) değişiminin klima
performansına etkisi araştırılmıştır. Elde edilen deneysel sonuçlardan sistemin Konya ilinde çalıştırılması ile Soğutma
Tesir Katsayısının (STK’nın) artan kompresör devri (1000 d/dk dan 3000d/dk) ile STK’nın 3.85’den 2.12’e kadar
düşerek azaldığı ve minimum STK’nın yaklaşık 2 olduğu görülmüştür. Performans deneylerinden elde edilen
sonuçların zamana bağlı değişimleri detaylı analiz edilerek, yorumlanmıştır.
Air conditioner system that has ranked among active safety systems is found in today’s vehicle as a
standard hardware. Power requirement of air conditioner is one of the most important loads on the vehicle engine,
which affects fuel economy and exhaust emissions of conventional and hybrid vehicles. Air conditioner system was
installed on a minibus in this study and the experimental system equipped with temperature, pressure and humidity
sensors, flow meter and power meter was tested at dynamic environmental conditions in order to determine air
conditioner performance for a parked condition. A constant capacity compressor, an expansion valve with external
compensation and R134a refrigerant were used in air conditioner. Effect of the compressor speed on air conditioner
performance was investigated when the air flow speed through evaporator is fixed (for the 8 m/s value of average air
speed in the channel). It was seen from the experimental results that Coefficient of Performance (COP) of the system
was decreased from 3.85 to 2.04 in case of the system operation in Konya when the compressor speed is risen from
1000 rpm to 3000 rpm and the minimum COP was approximately 2. Time dependent variation of the results from the
performance experiments were analyzed and interpreted.
yerleştirilen pürüzsüz art arda iki kürenin art izi bölgesinde oluşan akış yapısı Parçacık Görüntülemeli Hız Ölçme
(PIV) tekniği ile deneysel olarak araştırılmıştır. Su kanalında yapılan deneylerde, serbest akım hızına ve küre çapına
göre tanımlı Reynolds sayısı Re=5000’dir. Açık kanal hız değeri (0.118 m/s) sınır tabaka akışına neden olan levhanın
yaklaşık 63 mm üzerinde serbest akım değerlerine %1’den daha küçük bir farkla ulaştığı belirlendiği için,
hidrodinamik sınır tabaka kalınlığı 63 mm olarak saptanmıştır. Sınır tabaka akışı etkisinde olan konuma art arda
yerleştirilen pürüzsüz küreler etrafındaki akış yapısının ortalama akım çizgileri, akım yönündeki hız çalkantıları ve
Reynolds gerilmeleri küre çapı (D) ile küre-levha yüzeyi arasındaki boşluk (H) oranının 0≤H/D≤1.5 olduğu aralıkta
akış fiziğinde oluşan değişimleri belirlenmiştir. Küreler düz levhaya yakın konumlarında, levha ile kürelerin alt tarafı
arasında oluşan jet formundaki akış hem iki küre arasındaki bölgeyi etkilemekte, hem de aşağı akım yönündeki
kürelerin art izi bölgelerine enerji vererek akışın hareketliliğini arttırmaktadır. Bu karışım ısı transferi uygulamaları
açısından önemlidir. Küreler levha yüzeyinden uzaklaştıkça sınır tabaka etkisi azalmakta ancak iki küre arasındaki
açıklığın (G) küçük değerlerinde art izi bölgesinde dönümlü akış bölgesi küre levha arasındaki mesafeden bağımsız
olarak önemli oranda etkilenmektedir.
In this study, flow structure around two smooth spheres arranged tandem inside different elevations of a
hydrodynamically developed boundary layer over a flat plate is investigated experimentally via Particle Image
Velocimetry (PIV) technique. Reynolds number taken as 5000 based on the free-stream velocity and sphere diameter.
Hydrodynamic boundary layer thickness was determined as 63 mm since the open channel velocity (0.118 m/s) over
the flat plate causes boundary layer flow reaches to free stream velocity with a difference less than 1% of free stream
velocity. The time-averaged streamline patterns, streamwise velocity fluctuations and Reynolds stress correlations of
flow structure around tandem arranged two smooth spheres placed under boundary layer effect were investigated in
terms of sphere diameter (D) and sphere-plate gap (G) ratio changes between 0≤H/D≤1.5. While the spheres are in the
positions close to flat plate, the jet flow between flat plate and sphere creates flow mixing by energizing the flow field
between two spheres and the wake region of the sphere in the downstream direction. The mixing is important in terms
of heat transfer applications. As the spheres moves upward from the flat plate, the effect of the boundary layer
decreased, however, the recirculation region in the wake regions of the two spheres are significantly affected for the
smaller gaps between the spheres (G) as dependent of the distance between the sphere and plate.
birçok ısı değiştiricide kullanım şartlarına bağlı olarak farklı geometrilere sahip kanatçık olarak adlandırılan
genişletilmiş ısı transfer yüzeyleri kullanılmaktadır. Isı değiştirici kapasitesinin hesaplanabilmesi için ısı taşınım
katsayısının bilinmesi gerekir. Bununla beraber aynı akış şartlarında ve sıcaklık farkında farklı kanatlar ve geometriler
ile ısı taşınım katsayısı farklılık göstermektedir. Kanat geometrisine ve akış özelliklerine bağlı bu katsayısının
belirlenmesi için literatürde çeşitli deneysel ve sayısal yöntemler kullanılmaktadır. Deneysel yöntemlerden biri olan
Wilson Çizim tekniği, uygun deneysel sonuçlar kullanılarak belirli bir ısı değiştirici geometrisi için ısı taşınım
katsayılarının hesaplanmasına yönelik deneysel eşitlik üretmeye yarayan bir metottur. Wilson Tekniği özünde transfer
edilen ısı ile sıcaklık farkı arasında, akış ve akışkan özelliklerini de dikkate alarak bir bağıntı elde etmeye yarayan ve
deneysel ölçüme dayanan bir doğrusal eğri bulma yöntemidir. Böylece ısı taşınım katsayıları elde edilebilmekte ve
boyutsuz sayılar ile ısı transferine etki eden birçok parametre tek bir grafikle ifade edilebilmektedir.
Bu çalışmada, ticari olarak üretilen ara soğutucu amaçlı kullanılan çapraz akışlı, tek geçişli kompakt bir ısı
değiştiricinin ısıl performansını belirlemek için farklı şartlarda deneyler yapılmıştır. Çalışmada ayrıca, bahsedilen ısı
değiştirici için ε-NTU yöntemiyle bulunan toplam ısı transfer katsayısı ve Wilson Çizim Tekniği kullanılarak ısı
taşınım katsayılarının bulunması incelenmiştir. Ara soğutucudan geçen sıcak akışkanın ısı değiştiriciye giriş sıcaklığı
60, 80, 100 ve 120 oC olarak ayarlanmıştır. Seçilen ara soğutucu için dolgu havası tarafında Colburn j katsayısı
0,002866-0,003592 arasında değişmiştir. Elde edilen değerler üç farklı literatür verisi ile karşılaştırıldığında bir tanesi
ile ±%10 mertebesinde uyumlu olduğu bulunmuştur.
Fins as enhanced heat transfer surfaces with different geometries for various operational conditions are used
in a vast variety of heat exchangers in order to improve heat transfer amount and keep the pressure drop in allowable
limits. To calculate the heat transfer capacity of a heat exchanger, heat convection coefficients of the fluid streams
have to be known. Nonetheless, heat convection coefficients get different values for different fin geometries at same
flow conditions and temperature differences. Various experimental and numerical methods are utilized in the literature
for obtaining heat convection coefficients dependent to fin geometry and flow properties. As one of the experimental
methods, Wilson plot technique serves for empirical equation derivation in order to calculate heat convection
coefficients for certain heat exchanger geometry by using proper experimental results. In its essence, Wilson plot
technique is a linear curve fitting method dependent to experimental results that is useful for obtaining a correlation
between transferred heat and temperature difference considering flow and fluid properties. In this way heat convection
coefficients can be obtained and numerous factors affecting the heat transfer can be represented by few dimensionless
numbers in a single graphic.
In the present study, experiments were conducted for different experimental parameters in order to determine thermal
performance of a cross flow single pass compact heat exchanger which is used as a commercial intercooler. Additionally, the calculation of the heat convection coefficients using Wilson plot technique with overall heat transfer
coefficient obtained by means of ε-NTU method for the aforementioned heat exchanger is also discussed in the study.
The entrance temperature of the charge air to the intercooler was arranged as 60, 80,100 and 120 oC. Colburn j factor
changed between 0,002866-0,003592 for the selected intercooler. It was found that, obtained results are in consistency
with one of the three literature data at a ratio of ±10%.
Dolayısıyla silindir geometrilerine akışların hidrodinamik etkileri uygulamaya bağlı farklılıklar göstermektedir ve bu
etkilerin araştırılması birçok uygulamada tasarım, iyileştirme ve geliştirme faaliyetlerine katkıda bulunacaktır.
Yapılan çalışmada türbülanslı bir sınır tabaka içerisine düz pürüzsüz levha yüzeyinden farklı yüksekliklerde akışa dik
doğrultuda yatay olarak yerleştirilen silindir geometrisi etrafında oluşan akış yapısı ve buna bağlı hidrodinamik etkiler
Parçacık GörüntülemeLİ Hız Ölçme Yöntemi (PIV) ile incelenmiştir. Deneyler Selçuk Üniversitesi İleri Ar-Ge
Merkezi’nde bulunan PIV ölçme sistemi ve açık su kanalında yapılmıştır. Deneylerde kullanılan akrilik silindirin çapı
50 mm seçilmiştir ve silindir çapına bağlı Reynolds sayısı 10,000’dir. Levha yüzeyi ile silindirin alt noktası
arasındaki boşluk, silindir çapının 0, 0.25, 0.50, ve 1 katı olacak şekilde deneyler tekrarlanmıştır. Silindirin üzerine
yerleştirildiği düz plaka üzerinde türbülans sınır tabaka elde edebilmek için plakanın hücum kenarına yakın bölgede
türbülans oluşturucu bir çubuk (trip wire) kullanılmıştır. Sınır tabaka etkisi nedeniyle silindirin düz levhaya temas
ettiği durumda silindir yüzeyinde akış ayrılma noktasının arka noktalara doğru kaydığı ve art izinin literatürde iyi
bilinen laminer sınır tabaka etkisine göre daha dar olduğu gözlemlenmiştir. Silindir levha yüzeyinden uzaklaştıkça
silindirin alt kısmında ortaya çıkan jet akışı art izi bölgesini yukarı yönlendirerek uzatmaktadır. Levha yüzeyinde
oluşan sınır tabaka ile silindir yüzeyindeki akış ayrılması ve silindir ile levha arasındaki jet akış birbirini etkilemekte
ve karmaşık üç boyutlu düzensiz dönümlü bir art izine neden olmaktadır. Levha yüzeyinde bu şekilde oluşan şiddetli
akış, uygulamada aşınmalara, istenmeyen ses ve gürültülere neden olabilmektedir. Bu nedenle bu etkileşimleri
azaltmak amacıyla silindir çevresinde oluşan akış yapısını kontrol edici yöntemler geliştirilmesi gerekir.
Cylinder is a basic geometry that has applications with various forms in a lot of industrial and commercial
areas. Therefore hydraulic effects of fluids on cylinder geometries exhibit different characteristics depending on the
application and investigation for these different effects will contribute to design, improvement and development tasks
in a lot of applications. In the conducted study, flow structure around cylinder geometry placed horizontally
perpendicular to the flow direction at different elevations from the floor of flat smooth plate in a turbulent boundary
layer and hydrodynamic effects dependent to these were investigated via Particle Image Velocimetry (PIV).
Experiments were performed in an open water channel and PIV system of Selcuk University Advanced R&D center.
Plexiglas cylinder used in experiments has a diameter of 50 mm and Reynolds number based on the cylinder diameter
was 10,000. Experiments were repeated for each position at which the distance between the bottom point of the
cylinder and the flat plate were 0, 0.25, 0.50 and 1 times of the cylinder diameter. A tripwire was utilized in order to
stimulate a turbulent boundary layer on the flat plate and tripwire was placed near to a location at the leading edge of
the flat plate. It was observed that the separation point from the surface of the cylinder moved towards downstream
and delayed and wake region of the cylinder was narrower at the lower side of the cylinder comparing to upper side
because of velocity gradient of the boundary layer. Also jet flow occurred between down part of the cylinder and the
flat plate lead wake region to upward direction as the gap increased due to momentum transfer. Boundary layer over
the flat plate, flow separation over the cylinder and jet flow between the cylinder and the flat plate affect each other
and cause to a complex three dimensional unsteady wake comprising vortices. This kind of flow with high intensity
causes wear, unwanted noise and vibrations in application. Hence methods that can control the flow structure around
the cylinder should be developed in order to reduce these kinds of interaction effects.
circular cylindrical geometries in various industrial and daily life applications must be known in respect of energy efficiency and stability for different flow conditions. In this sense, flow structures in the wake of a circular cylinder located in a boundary layer flow and a flow region near to free flow surface were examined by means of PIV system in an open water channel. Circular cylinder was parallel to boundary layer plate and perpendicular to flow direction. Experiments were conducted primarily in a region near to the free surface of the flow and then in the boundary layer flow at various locations of the cylinder diameter (D) ratios of contacting case, 0.00D, 0.25D, 0.50D and 1.0D. Cylinder diameter was 50 mm and Reynolds number calculated according to this diameter was selected 5000.
For the experiments, Stereo Particle Image Velocimetry Setup in Selcuk University Mechanical Engineering Department
Hydraulic Laboratory was utilized. Results obtained as the
consequence of investigation of flow around circular cylinder at different flow conditions are presented in the form of time
averaged streamwise velocity component contours and timeaveraged vorticity contours. It is shown that wake structures of circular cylinder immersed in a boundary layer flow exhibited considerably different characteristics compared to the flow structures obtained at flow region near to free surface of the flow.
various non-circular cylinders located in a shallow water flow. Free Stream flow velocity of the shallow water was
adjusted to obtain the Reynolds numbers i.e. 5000 and 10000 based on the characteristic length of each cylinder. A
circular cylinder was also tested in order to establish results for comparison of ellipse, triangle, rectangle and square
cross-section cylinders. Measurement plane was parallel to the boundary layer plate and at the middle point of the
immersed parts of cylinders. Interactions between stream free surface and boundary layer flow, and non-circular
cylinder geometries were evaluated in respect of physics of flow phenomenon. Ellipse and rectangular cylinders form
very small wake regions and vortex streets yield narrower wake structure when compared to the square and triangular
cylinders. In triangular cylinder case, two different placements that were sharp edge faced towards upstream and
sharp edge directed to downstream were done. It was demonstrated that wider wake region for the sharp-edge towards
the downstream case was occurred while it was nearly half of the wake region of the sharp-edge directed to
downstream case. Quantitative results are also presented in the paper by means of color scales and contour lines to
make more distinctive comparison. Results can be used in evaluation of various construction and design studies as
well as computational fluid dynamics applications according to Reynolds Number analogy.
and in-lined arrangements were experimentally investigated. The experiments were conducted employing a Particle
Image Velocimetry (PIV) system and Rhodamine 6G dye method in a water channel at Re=5000. A peculiar geometry
of sphere/Spheres orients the instantaneous flow characteristics around sphere/spheres to be profoundly three
dimensional as well as unsteady in the wake region. It was demonstrated that all of the arrangements developed a very
chaotic structure in the wake region. In addition, time-averaged flow patterns such as streamline topology, velocity
components, rms velocities in x and y directions were fairly symmetrical with respect to the sphere equator line. Dual
sphere experiments were performed with three altered gap ratios (G/D) of spheres, for example, G/D=1.0, 1.5 and 2.0.
Here, G is the length between the focal points of the spheres and D is the sphere diameter. In comparison to a sphere
case, at G/D=1.0, appearances of wake of dual spheres are identical to a single sphere case but the wake expands to a
larger size. A jet flow at G/D=1.5 occurs between the spheres for three different arrangements. For G/D=2.0, the wake
for each sphere becomes a separated region and the effect of jet like flow disappears more or less completely. The
results obtained in this study can be a fruitful source for developing and validation of new codes both in scientific and
commercial manner.
region of the spheres was investigated with a Particle Image Velocimetry (PIV) system when the spheres were
in a boundary layer over a flat plate as a special case. Reynolds number was 5000 based on the sphere diameter
which was 42.5 mm. Boundary layer was tripped 8mm away from the leading edge of the flat plate with a 5
mm trip wire. The thickness of the hydrodynamically developed boundary layer was determined as 63mm
which was larger than the sphere diameter of D=42.5mm. Wake region of the spheres was examined from point
of flow physics for the different sphere locations in the ranges of 0G/D 1.5 and 0S/D 1.5 where G and S
were the distance between the spheres and the distance between the bottom point of the spheres and the flat
plate surface, respectively. Depending on the different sphere locations, instantaneous and time averaged
vorticity data, scalar values of time-averaged velocity components and their root mean square (rms) values and
time averaged vorticity data are presented in the study for the evaluation of wake region of the spheres. It is
demonstrated that the gap between the two spheres and the interaction between the gap and the boundary layer
greatly affects flow pattern, especially when spheres are located near to the flat plate surface, i.e. S/D=0.1 for
0G/D 1.5. Different distances between the spheres resulted in various flow patterns as the spheres were
approached to the flat plate. The distance S/D=0.1 for all gap values has the strongest effect on the wake
structures. Beyond G/D=1.0, the sphere wakes tend to be similar to single sphere case. The instantaneous
vorticity fields of the side by side arrangements comprised wavy structures in higher level comparing to an
individual sphere case. The gap flow intensifies the occurrence of small scale eddies in the wake region. The
submersion rate of the spheres actually determines the characteristics of the wake region and is affected from
boundary layer flow in a gradually decreasing manner.
debimetreler kullanılmaktadır. Bu cihazlar bilgi maliyeti, navlun, vergiler gibi maliyetlerden dolayı
kullanıcı için pahalı bir çözümdür. Ayrıca genellikle stok tutulmadığı için kullanıcının 4 ila 8 hafta gibi
uzun süreler beklemesi gerekmektedir. Bununla beraber gelen ürünlerin kullanımında, bir arıza
durumunda müdahalede ve kalibrasyon konularında sınırlı teknik destek söz konusudur.
Bu çalışmada ithal debimetrelere alternatif olarak geleneksel ventüri tüpü ve bir elektronik veri toplama
düzeneği kullanarak debi ölçümü ve sonuçları incelenmiştir. Biri sıvı diğeri ise gaz olmak üzere iki
farklı akışkanın debilerinin ölçülmesi için iki farklı ventüri tüpü hazırlanmıştır ve aynı elektronik veri
toplama düzeneğinde ölçümler kaydedilerek hesaplamalar yapılmıştır. Akışkanlardan gaz olan hava,
sıvı olan ise ST42 numaralı endüstriyel yağdır. Yağ akışkan, ölçümler sırasında 100 oC sıcaklığa
kadar ısıtılmıştır. Çalışma sonuçlarına göre ventüri tüpünün dinamik debi ölçümünde dahi etkin
biçimde kullanılabileceği gösterilmiştir.
seçiminde önemli kriterler ısı transferi ve basınç düşüşü performansı, maliyet, kompaktlık ve etkenlik
olarak sıralanabilir. Bununla birlikte son yıllarda enerji kullanımına yönelik yapılan çalışmalar farklı
sistemlerdeki enerji kullanılabilirliğinin yani ekserjinin de değerlendirilmesi gerektiğini ortaya
koymaktadır. Aynı zamanda ikinci yasa yaklaşımı, bir optimizasyon problemi olan ısı değiştirici
tasarımında da yer almaktadır.
Yapılan çalışmada 650-670 kompaktlık oranına sahip üç farklı tipteki ısı değiştirici 0.027-0.16 ısıl
kapasite oranlarında deneysel olarak incelenmiştir. İnceleme sonuçları kullanılarak ısı değiştiricilerinde
gerçekleşen ekserji yıkımı hesaplanmıştır. Ekserji yıkım değerleri açısından ısı değiştiricileri
karşılaştırılmıştır. Karşılaştırma sırasında ısı değiştiricilerin ısı transferi yüzey alanlarının dağılımı,
tersinmezlik değerleri, tersinmezliğin sıcaklık ve basınç bileşenleri ve ekserji verimleri kullanılmıştır.
Heat transfer and pressure drop performance, cost, compactness and effectiveness can be listed as
important criteria for selection of widely utilized compact heat exchangers in buildings and a lot of
other industrial areas. Nevertheless, recent studies intended for energy usage presents that usability
of the energy, namely exergy, should be evaluated for various systems. The second law approach is
also used for heat exchanger design which is an optimization problem.
In this work, three different type heat exchangers having 650-670 compactness ratios were
experimentally investigated between 0.027-0.16 heat capacity ratios. Exergy destruction occurred in
the heat exchangers were calculated using the investigation results. Distribution of heat transfer
surface area of the heat exchangers, irreversibility rates, temperature and pressure components of the
irreversibility and exergy efficiency were used for comparison.
applications such as bridge legs, electricity production from vortex induced
vibrations, petroleum and natural gas lines, off-shore and on shore structures and
wind turbine bodies. Flow structures around these geometries have important effects
on forces acting upon these geometries. Therefore, performances of industrial
designs can be improved by controlling flow structure.
Experiments were carried out in an open water channel at Mechanical
Engineering Department of Selcuk University. In the present study, flow structure
around a cylinder with circular cross section was investigated via Particle Image
Velocimetry (PIV) technique in uniform flow condition. Thereafter a knitted porous
structure was wrapped around the cylinder in order to apply a passive flow control in
the wake structure of the cylinder. Free stream velocity during the experiments was
arranged as the Reynolds number based on the cylinder diameter of 50mm was
10000. Velocity vector field, streamline topology, streamwise velocity components
and Reynolds stress correlations were used in order to explain flow structure around
the cylinders for the sake of comparison. At the end of the experiments, it was
realized that the porous knitted structure extended the size of wake and elongated
wake length of the cylinder and increased the velocity distributions in the wake
while decreasing the strength. The wake was extended approximately half cylinder
diameter in width and elongated approximately one cylinder diameter in length
when the passive flow control was applied. The size of foci points in the wake of the
cylinder without passive control were evaluated as they were relatively small
comparing to the that of the cylinder with passive control. In the wake of the
cylinder with passive control, a saddle point occurred in the further downstream
comparing to the wake of the cylinder without passive flow control. This study
presents to control the flow around a circular cylinder through the implementation of
artificial surface roughness by a knitted coating around the cylinder, which has a
good agreement from the point of flow physics in the literature. These results will be
useful for industrial applications, ocean engineering and ocean energy production
via various similarity approaches. In the future, the knitted structure forming
circular, diamond or trapeze patterns will be tested.
of basic fluid dynamics research. These basic researches include experimental flow
field measurements and also computational fluid dynamics (CFD) analyses. A
particular part of aforementioned studies focus on ocean structures, particularly used
in energy generation, since they contains various basic geometrical shapes. Results
are often presented flow characteristics as free stream velocity, pressure values and
vibrations, vortex induced vibrations. Time Averaged Particle Image Velocimetry
(PIV) is one of the experimental measurement techniques. This technique comprises
instant and time averaged measurement of a complete flow field in respect of flow
velocity. Instant and time averaged vector field, stream lines, scalar value distributions of velocity fluctuations, Reynolds stress correlations, normalized u and
v velocity components and vorticity can be derived.
In this study, two independent spheres were placed in a turbulent boundary
layer in a 30 degree angled tandem position in order to simulate an ocean bottom
situation and interaction between boundary layer and wake regions of the spheres
were investigated with a PIV setup. Results were presented with visual and scalar
data. Thirty five different angled tandem array sphere positions were investigated
experimentally in boundary layer flow for instantaneous velocity vectors, time
averaged velocity vectors, stream lines, scalar values of velocity components, their
RMS values, Reynolds stress. Boundary layer greatly effects flow pattern, especially
when spheres were located within the boundary layer. Different distances between
the spheres yielded dissimilar results. After a specified height from the surface,
evolution of the flow patterns depended to the gap between spheres were
approximately predictable, which is also an indication to ineffective boundary layer
flow. The instantaneous vorticity fields reveal an unsteady wavy structure of the
sphere wake. The concentration of small scale vortices (eddy) is more dominant in
the wake of the sphere when the gap is initiated. It is demonstrated that the presence
of boundary layer flow over the flat plate generates significant complications into
the wake of the spheres due to non-uniform velocity profile, gap flow between the
bottom section of the spheres and flat plate surface. The non-uniform velocity
profile of the boundary layer flow causes a difference in the celerity of the vortex
shedding from the periphery of the spheres. Owing to the jet flow, the periodic
changing of high and low pressure zones in the wake region disappears resulting in
breaking large scale vortices. For real world and ocean energy applications including
elements with spherical shapes, data from present work will be very useful to
evaluate, especially for drag and lift forces, flow induced vibrations, pressure
gradients obtained by means of numerical investigations.
silindirin art izi ile serbest yüzey etkileşimi incelenmiştir. Deneysel çalışma için Selçuk Üniversitesi İleri Ar-Ge
Merkezi’nde bulunan açık su kanalında, Parçacık Görüntüleme Hız Ölçüm (PIV) sistemi kullanılmıştır. Deneyler,
silindirin üst noktası ve serbest yüzey arasındaki mesafe (h) ile silindir çapının (D) oranı olan h/D=0, 0.25, 0.50 ve
1.0 değerlerinde yapılmıştır. Serbest akış hızı (U∞=200mm/s) ve silindir çapı (D=50mm) ile tarif edilen Reynolds
sayısı 10000 olarak seçilmiştir. Froude sayısı su derinliğine bağlı olarak
Fr U ghw =0.095 hesaplanmış olup 1'
den küçük olduğu için serbest yüzey kritik altı akış şartlarındadır. Serbest yüzey ve silindir art izi etkileşimini
incelemek için, zaman ortalaması hesaplanan hız vektörleri, akım çizgileri ve akış doğrultusundaki hız bileşenleri
kullanılmıştır. Serbest yüzey etkisinden dolayı silindirin art izi önemli oranda etkilenmekte, bu bölgedeki akışın enerji
yoğunluğu ve dönüm miktarı değişmektedir. Silindir yüzeye temas ettiğinde, silindirin altında kalan bölgede
sürekliliği sağlamak için akış oldukça hızlanmaktadır. Silindir daldırma miktarı arttıkça, özellikle silindirin üst
kısmından geçen akıştan kaynaklanan momentum transferi nedeniyle art izi bir miktar kısalmaktadır. Serbest yüzeyin
sönümleme etkisi art izini etkilemekte ve silindir serbest yüzeyden uzaklaştıkça yüzey etkisi azalmaktadır ve ayrılmış
akış yüzeyle birleşmemektedir. Daldırma oranı h/D=1.0 oranında ise serbest yüzeyin etkisi ihmal edilebilir mertebede
olmakta ve zaman ortalaması alınmış akışın art izi yapısı simetriğe yaklaşmaktadır.
Experimental results of interaction between fluid free surface and wake region of a horizontal smooth
cylinder beneath the free surface region in an open water channel flow are presented. Experiments were performed in
a large-scale open water channel at Selcuk University Advanced Research Center via Particle Image Velocimetry
(PIV) system. The experiments were carried out for the different cylinder locations at different depth ratios of h/D=
0, 0.25. 0.50 and 1. Here, h is the gap between the top point of the cylinder and free surface, and D is the diameter of
the cylinder. During the experiments, the Reynolds number based on the cylinder diameter (D=50mm) and free
stream velocity (U∞=200mm/s) was taken as Re=10000. The Froude number based on the water depth (hw) was
Fr U ghw =0.095 depending on the free-stream velocity, which was subcritical flow region owing to the
Froude number less than 1. Time-averaged velocity vector field, streamline topology and streamwise velocity
components were used in order to explain flow structure between the free surface and the cylinder wake region. Due
to the effect of free surface, the wake region of the cylinder is significantly affected so that energy intensity and
recirculation length are changed. When upper side of the cylinder is contacted to free surface, velocity flow in the
bottom side of the cylinder is accelerated due to the energy conversion and blockage effect. As the submerging ratio
increases, the wake region of the cylinder becomes shorter due to the momentum transfer from the upper side of the
cylinder. By increasing the submerging ratio, the effect of the free surface became less and the separated flow from
the periphery of the cylinder was not reattached to the free surface. It is observed that the effect of the free surface on
flow structure is negligible at submerging ratio of h/D=1.0 and time averaged wake region structure become nearly
symmetric.
çalışmada, art arda yerleştirilmiş iki küre ile serbest su yüzeyinin etkileşimi, parçacık görüntülemeli hız ölçme
yöntemi (PIV) ile kürelerin değişik daldırma oranlarında ve farklı açıklık oranlarında araştırılmıştır. Deneyler,
kürelerin serbest yüzeyden itibaren daldırma oranının 0.25≤h/D≤2.0 aralığında ve iki kürenin birbirine temas ettiği
durumdan aralarındaki açıklığın 1.0≤G/D≤2.5 aralığında değiştiği ve küre çapına göre tarif edilen Reynolds sayısının
5000 değeri için yapılmıştır. Elde edilen sonuçlar anlık girdap eş düzey eğrileri, akım çizgileri, akım yönündeki hız
değerleri ve çalkantı hızlarının değişimleri olarak sunulmuştur. Serbest yüzeyin akış yapısına etkisinin daldırma
oranının h/D=1.0 olduğu duruma kadar devam ettiği görülmüştür. Daldırma oranı arttıkça, kürelerin açıklık oranının
G/D=2.50 olduğu durumda ön kısımda bulunan kürenin art izindeki akış yapısı simetrik bir hal almaktadır. Açıklık
oranı G/D=1.0 olduğu durum haricinde, ön tarafta bulunan kürelerin tüm açıklık oranlarında art izi bölgesinde iki adet
odak noktasının oluştuğu sadece h/D=2.0 daldırma oranında elde edilmiştir. Farklı daldırma oranlarında küreler
etrafından ayrılan akış, serbest yüzeyle birleşmeden serbest akım hızıyla sönümlenerek yoluna devam etmektedir.
Kürenin alt ve üst kısmından kopan negatif ve pozitif girdaplar ile küre etrafındaki akış yapısının türbülanslı ve çok
karmaşık olduğu anlık girdap eş düzey eğrilerinden tespit edilmiştir. İki küre arasındaki mesafe ve kürelerin daldırma
oranları arttıkça, küreler çevresindeki akış yapısının birbirinden bağımsız yerleştirilmiş iki kürede oluşan art izine
benzemektedir.
In this study, in order to investigate the flow structure formed by fluid-body interaction and to determine
effective spacing ratio, interaction between free water surface and tandem arranged of the two spheres was
investigated via Particle Image Velocimetry method with various submerging ratios and at different spacing ratios of
spheres. Experiments were carried out with submerging ratios of 0.25≤h/D≤2.0 and spacing ratios of 1.0≤G/D≤2.5,
and Reynolds number value, which is defined based on the sphere diameter, taken as 5000. The obtained results were
presented as instantaneous vorticity, time-averaged streamline patterns, streamwise velocity components and
streamwise velocity fluctuations. It is observed that the effect of free surface on flow structure until submerging ratio
of h/D=1.0. In the case of spacing ratio for 2.50, as submerging ratio increases, the flow structure at the wake region
of sphere at front becomes symmetrical. For h/D=2.0, at the wake region of sphere at front two foci points formed for
all spacing ratios apart from G/D=1.0. The flow separated from the periphery of the spheres continued downstream as
suppressed without reattaching to the free surface for different submerging ratios. From the instantaneous vorticity
contour maps comprised data from vortices shed from upper and down parts of the sphere, it was realized that flow
structure is very turbulent and chaotic. As the distance between the two spheres and the submerging ratio get bigger,
flow around spheres gets similar to the flow around two independent spheres in different flow mediums.
bulunmaktadır. Klima sistemi, konvensiyonel ve hibrit taşıtların yakıt ekonomisini ve emisyonlarını etkileyen en
önemli yüklerdendir. Bu çalışma da, taşıt klima sistemi bir minibüs üzerine kurulmuş, klima performansını belirlemek
amacıyla sıcaklık, basınç ve nem sensörleri, debi ölçer ve güç ölçer cihazları ile donatılan sistem yaz aylarında
dinamik çevre şartlarında test edilmiştir. Çalışmada, evaporatör üzerinden geçen hava debisinin sabit olması
durumunda (kanal içerisindeki ortalama hızının 8 m/s değeri için), kompresör hızının (devrinin) değişiminin klima
performansına etkisi araştırılmıştır. Elde edilen deneysel sonuçlardan sistemin Konya ilinde çalıştırılması ile Soğutma
Tesir Katsayısının (STK’nın) artan kompresör devri (1000 d/dk dan 3000d/dk) ile STK’nın 3.85’den 2.12’e kadar
düşerek azaldığı ve minimum STK’nın yaklaşık 2 olduğu görülmüştür. Performans deneylerinden elde edilen
sonuçların zamana bağlı değişimleri detaylı analiz edilerek, yorumlanmıştır.
Air conditioner system that has ranked among active safety systems is found in today’s vehicle as a
standard hardware. Power requirement of air conditioner is one of the most important loads on the vehicle engine,
which affects fuel economy and exhaust emissions of conventional and hybrid vehicles. Air conditioner system was
installed on a minibus in this study and the experimental system equipped with temperature, pressure and humidity
sensors, flow meter and power meter was tested at dynamic environmental conditions in order to determine air
conditioner performance for a parked condition. A constant capacity compressor, an expansion valve with external
compensation and R134a refrigerant were used in air conditioner. Effect of the compressor speed on air conditioner
performance was investigated when the air flow speed through evaporator is fixed (for the 8 m/s value of average air
speed in the channel). It was seen from the experimental results that Coefficient of Performance (COP) of the system
was decreased from 3.85 to 2.04 in case of the system operation in Konya when the compressor speed is risen from
1000 rpm to 3000 rpm and the minimum COP was approximately 2. Time dependent variation of the results from the
performance experiments were analyzed and interpreted.
yerleştirilen pürüzsüz art arda iki kürenin art izi bölgesinde oluşan akış yapısı Parçacık Görüntülemeli Hız Ölçme
(PIV) tekniği ile deneysel olarak araştırılmıştır. Su kanalında yapılan deneylerde, serbest akım hızına ve küre çapına
göre tanımlı Reynolds sayısı Re=5000’dir. Açık kanal hız değeri (0.118 m/s) sınır tabaka akışına neden olan levhanın
yaklaşık 63 mm üzerinde serbest akım değerlerine %1’den daha küçük bir farkla ulaştığı belirlendiği için,
hidrodinamik sınır tabaka kalınlığı 63 mm olarak saptanmıştır. Sınır tabaka akışı etkisinde olan konuma art arda
yerleştirilen pürüzsüz küreler etrafındaki akış yapısının ortalama akım çizgileri, akım yönündeki hız çalkantıları ve
Reynolds gerilmeleri küre çapı (D) ile küre-levha yüzeyi arasındaki boşluk (H) oranının 0≤H/D≤1.5 olduğu aralıkta
akış fiziğinde oluşan değişimleri belirlenmiştir. Küreler düz levhaya yakın konumlarında, levha ile kürelerin alt tarafı
arasında oluşan jet formundaki akış hem iki küre arasındaki bölgeyi etkilemekte, hem de aşağı akım yönündeki
kürelerin art izi bölgelerine enerji vererek akışın hareketliliğini arttırmaktadır. Bu karışım ısı transferi uygulamaları
açısından önemlidir. Küreler levha yüzeyinden uzaklaştıkça sınır tabaka etkisi azalmakta ancak iki küre arasındaki
açıklığın (G) küçük değerlerinde art izi bölgesinde dönümlü akış bölgesi küre levha arasındaki mesafeden bağımsız
olarak önemli oranda etkilenmektedir.
In this study, flow structure around two smooth spheres arranged tandem inside different elevations of a
hydrodynamically developed boundary layer over a flat plate is investigated experimentally via Particle Image
Velocimetry (PIV) technique. Reynolds number taken as 5000 based on the free-stream velocity and sphere diameter.
Hydrodynamic boundary layer thickness was determined as 63 mm since the open channel velocity (0.118 m/s) over
the flat plate causes boundary layer flow reaches to free stream velocity with a difference less than 1% of free stream
velocity. The time-averaged streamline patterns, streamwise velocity fluctuations and Reynolds stress correlations of
flow structure around tandem arranged two smooth spheres placed under boundary layer effect were investigated in
terms of sphere diameter (D) and sphere-plate gap (G) ratio changes between 0≤H/D≤1.5. While the spheres are in the
positions close to flat plate, the jet flow between flat plate and sphere creates flow mixing by energizing the flow field
between two spheres and the wake region of the sphere in the downstream direction. The mixing is important in terms
of heat transfer applications. As the spheres moves upward from the flat plate, the effect of the boundary layer
decreased, however, the recirculation region in the wake regions of the two spheres are significantly affected for the
smaller gaps between the spheres (G) as dependent of the distance between the sphere and plate.
birçok ısı değiştiricide kullanım şartlarına bağlı olarak farklı geometrilere sahip kanatçık olarak adlandırılan
genişletilmiş ısı transfer yüzeyleri kullanılmaktadır. Isı değiştirici kapasitesinin hesaplanabilmesi için ısı taşınım
katsayısının bilinmesi gerekir. Bununla beraber aynı akış şartlarında ve sıcaklık farkında farklı kanatlar ve geometriler
ile ısı taşınım katsayısı farklılık göstermektedir. Kanat geometrisine ve akış özelliklerine bağlı bu katsayısının
belirlenmesi için literatürde çeşitli deneysel ve sayısal yöntemler kullanılmaktadır. Deneysel yöntemlerden biri olan
Wilson Çizim tekniği, uygun deneysel sonuçlar kullanılarak belirli bir ısı değiştirici geometrisi için ısı taşınım
katsayılarının hesaplanmasına yönelik deneysel eşitlik üretmeye yarayan bir metottur. Wilson Tekniği özünde transfer
edilen ısı ile sıcaklık farkı arasında, akış ve akışkan özelliklerini de dikkate alarak bir bağıntı elde etmeye yarayan ve
deneysel ölçüme dayanan bir doğrusal eğri bulma yöntemidir. Böylece ısı taşınım katsayıları elde edilebilmekte ve
boyutsuz sayılar ile ısı transferine etki eden birçok parametre tek bir grafikle ifade edilebilmektedir.
Bu çalışmada, ticari olarak üretilen ara soğutucu amaçlı kullanılan çapraz akışlı, tek geçişli kompakt bir ısı
değiştiricinin ısıl performansını belirlemek için farklı şartlarda deneyler yapılmıştır. Çalışmada ayrıca, bahsedilen ısı
değiştirici için ε-NTU yöntemiyle bulunan toplam ısı transfer katsayısı ve Wilson Çizim Tekniği kullanılarak ısı
taşınım katsayılarının bulunması incelenmiştir. Ara soğutucudan geçen sıcak akışkanın ısı değiştiriciye giriş sıcaklığı
60, 80, 100 ve 120 oC olarak ayarlanmıştır. Seçilen ara soğutucu için dolgu havası tarafında Colburn j katsayısı
0,002866-0,003592 arasında değişmiştir. Elde edilen değerler üç farklı literatür verisi ile karşılaştırıldığında bir tanesi
ile ±%10 mertebesinde uyumlu olduğu bulunmuştur.
Fins as enhanced heat transfer surfaces with different geometries for various operational conditions are used
in a vast variety of heat exchangers in order to improve heat transfer amount and keep the pressure drop in allowable
limits. To calculate the heat transfer capacity of a heat exchanger, heat convection coefficients of the fluid streams
have to be known. Nonetheless, heat convection coefficients get different values for different fin geometries at same
flow conditions and temperature differences. Various experimental and numerical methods are utilized in the literature
for obtaining heat convection coefficients dependent to fin geometry and flow properties. As one of the experimental
methods, Wilson plot technique serves for empirical equation derivation in order to calculate heat convection
coefficients for certain heat exchanger geometry by using proper experimental results. In its essence, Wilson plot
technique is a linear curve fitting method dependent to experimental results that is useful for obtaining a correlation
between transferred heat and temperature difference considering flow and fluid properties. In this way heat convection
coefficients can be obtained and numerous factors affecting the heat transfer can be represented by few dimensionless
numbers in a single graphic.
In the present study, experiments were conducted for different experimental parameters in order to determine thermal
performance of a cross flow single pass compact heat exchanger which is used as a commercial intercooler. Additionally, the calculation of the heat convection coefficients using Wilson plot technique with overall heat transfer
coefficient obtained by means of ε-NTU method for the aforementioned heat exchanger is also discussed in the study.
The entrance temperature of the charge air to the intercooler was arranged as 60, 80,100 and 120 oC. Colburn j factor
changed between 0,002866-0,003592 for the selected intercooler. It was found that, obtained results are in consistency
with one of the three literature data at a ratio of ±10%.
Dolayısıyla silindir geometrilerine akışların hidrodinamik etkileri uygulamaya bağlı farklılıklar göstermektedir ve bu
etkilerin araştırılması birçok uygulamada tasarım, iyileştirme ve geliştirme faaliyetlerine katkıda bulunacaktır.
Yapılan çalışmada türbülanslı bir sınır tabaka içerisine düz pürüzsüz levha yüzeyinden farklı yüksekliklerde akışa dik
doğrultuda yatay olarak yerleştirilen silindir geometrisi etrafında oluşan akış yapısı ve buna bağlı hidrodinamik etkiler
Parçacık GörüntülemeLİ Hız Ölçme Yöntemi (PIV) ile incelenmiştir. Deneyler Selçuk Üniversitesi İleri Ar-Ge
Merkezi’nde bulunan PIV ölçme sistemi ve açık su kanalında yapılmıştır. Deneylerde kullanılan akrilik silindirin çapı
50 mm seçilmiştir ve silindir çapına bağlı Reynolds sayısı 10,000’dir. Levha yüzeyi ile silindirin alt noktası
arasındaki boşluk, silindir çapının 0, 0.25, 0.50, ve 1 katı olacak şekilde deneyler tekrarlanmıştır. Silindirin üzerine
yerleştirildiği düz plaka üzerinde türbülans sınır tabaka elde edebilmek için plakanın hücum kenarına yakın bölgede
türbülans oluşturucu bir çubuk (trip wire) kullanılmıştır. Sınır tabaka etkisi nedeniyle silindirin düz levhaya temas
ettiği durumda silindir yüzeyinde akış ayrılma noktasının arka noktalara doğru kaydığı ve art izinin literatürde iyi
bilinen laminer sınır tabaka etkisine göre daha dar olduğu gözlemlenmiştir. Silindir levha yüzeyinden uzaklaştıkça
silindirin alt kısmında ortaya çıkan jet akışı art izi bölgesini yukarı yönlendirerek uzatmaktadır. Levha yüzeyinde
oluşan sınır tabaka ile silindir yüzeyindeki akış ayrılması ve silindir ile levha arasındaki jet akış birbirini etkilemekte
ve karmaşık üç boyutlu düzensiz dönümlü bir art izine neden olmaktadır. Levha yüzeyinde bu şekilde oluşan şiddetli
akış, uygulamada aşınmalara, istenmeyen ses ve gürültülere neden olabilmektedir. Bu nedenle bu etkileşimleri
azaltmak amacıyla silindir çevresinde oluşan akış yapısını kontrol edici yöntemler geliştirilmesi gerekir.
Cylinder is a basic geometry that has applications with various forms in a lot of industrial and commercial
areas. Therefore hydraulic effects of fluids on cylinder geometries exhibit different characteristics depending on the
application and investigation for these different effects will contribute to design, improvement and development tasks
in a lot of applications. In the conducted study, flow structure around cylinder geometry placed horizontally
perpendicular to the flow direction at different elevations from the floor of flat smooth plate in a turbulent boundary
layer and hydrodynamic effects dependent to these were investigated via Particle Image Velocimetry (PIV).
Experiments were performed in an open water channel and PIV system of Selcuk University Advanced R&D center.
Plexiglas cylinder used in experiments has a diameter of 50 mm and Reynolds number based on the cylinder diameter
was 10,000. Experiments were repeated for each position at which the distance between the bottom point of the
cylinder and the flat plate were 0, 0.25, 0.50 and 1 times of the cylinder diameter. A tripwire was utilized in order to
stimulate a turbulent boundary layer on the flat plate and tripwire was placed near to a location at the leading edge of
the flat plate. It was observed that the separation point from the surface of the cylinder moved towards downstream
and delayed and wake region of the cylinder was narrower at the lower side of the cylinder comparing to upper side
because of velocity gradient of the boundary layer. Also jet flow occurred between down part of the cylinder and the
flat plate lead wake region to upward direction as the gap increased due to momentum transfer. Boundary layer over
the flat plate, flow separation over the cylinder and jet flow between the cylinder and the flat plate affect each other
and cause to a complex three dimensional unsteady wake comprising vortices. This kind of flow with high intensity
causes wear, unwanted noise and vibrations in application. Hence methods that can control the flow structure around
the cylinder should be developed in order to reduce these kinds of interaction effects.
circular cylindrical geometries in various industrial and daily life applications must be known in respect of energy efficiency and stability for different flow conditions. In this sense, flow structures in the wake of a circular cylinder located in a boundary layer flow and a flow region near to free flow surface were examined by means of PIV system in an open water channel. Circular cylinder was parallel to boundary layer plate and perpendicular to flow direction. Experiments were conducted primarily in a region near to the free surface of the flow and then in the boundary layer flow at various locations of the cylinder diameter (D) ratios of contacting case, 0.00D, 0.25D, 0.50D and 1.0D. Cylinder diameter was 50 mm and Reynolds number calculated according to this diameter was selected 5000.
For the experiments, Stereo Particle Image Velocimetry Setup in Selcuk University Mechanical Engineering Department
Hydraulic Laboratory was utilized. Results obtained as the
consequence of investigation of flow around circular cylinder at different flow conditions are presented in the form of time
averaged streamwise velocity component contours and timeaveraged vorticity contours. It is shown that wake structures of circular cylinder immersed in a boundary layer flow exhibited considerably different characteristics compared to the flow structures obtained at flow region near to free surface of the flow.
various non-circular cylinders located in a shallow water flow. Free Stream flow velocity of the shallow water was
adjusted to obtain the Reynolds numbers i.e. 5000 and 10000 based on the characteristic length of each cylinder. A
circular cylinder was also tested in order to establish results for comparison of ellipse, triangle, rectangle and square
cross-section cylinders. Measurement plane was parallel to the boundary layer plate and at the middle point of the
immersed parts of cylinders. Interactions between stream free surface and boundary layer flow, and non-circular
cylinder geometries were evaluated in respect of physics of flow phenomenon. Ellipse and rectangular cylinders form
very small wake regions and vortex streets yield narrower wake structure when compared to the square and triangular
cylinders. In triangular cylinder case, two different placements that were sharp edge faced towards upstream and
sharp edge directed to downstream were done. It was demonstrated that wider wake region for the sharp-edge towards
the downstream case was occurred while it was nearly half of the wake region of the sharp-edge directed to
downstream case. Quantitative results are also presented in the paper by means of color scales and contour lines to
make more distinctive comparison. Results can be used in evaluation of various construction and design studies as
well as computational fluid dynamics applications according to Reynolds Number analogy.
and in-lined arrangements were experimentally investigated. The experiments were conducted employing a Particle
Image Velocimetry (PIV) system and Rhodamine 6G dye method in a water channel at Re=5000. A peculiar geometry
of sphere/Spheres orients the instantaneous flow characteristics around sphere/spheres to be profoundly three
dimensional as well as unsteady in the wake region. It was demonstrated that all of the arrangements developed a very
chaotic structure in the wake region. In addition, time-averaged flow patterns such as streamline topology, velocity
components, rms velocities in x and y directions were fairly symmetrical with respect to the sphere equator line. Dual
sphere experiments were performed with three altered gap ratios (G/D) of spheres, for example, G/D=1.0, 1.5 and 2.0.
Here, G is the length between the focal points of the spheres and D is the sphere diameter. In comparison to a sphere
case, at G/D=1.0, appearances of wake of dual spheres are identical to a single sphere case but the wake expands to a
larger size. A jet flow at G/D=1.5 occurs between the spheres for three different arrangements. For G/D=2.0, the wake
for each sphere becomes a separated region and the effect of jet like flow disappears more or less completely. The
results obtained in this study can be a fruitful source for developing and validation of new codes both in scientific and
commercial manner.
region of the spheres was investigated with a Particle Image Velocimetry (PIV) system when the spheres were
in a boundary layer over a flat plate as a special case. Reynolds number was 5000 based on the sphere diameter
which was 42.5 mm. Boundary layer was tripped 8mm away from the leading edge of the flat plate with a 5
mm trip wire. The thickness of the hydrodynamically developed boundary layer was determined as 63mm
which was larger than the sphere diameter of D=42.5mm. Wake region of the spheres was examined from point
of flow physics for the different sphere locations in the ranges of 0G/D 1.5 and 0S/D 1.5 where G and S
were the distance between the spheres and the distance between the bottom point of the spheres and the flat
plate surface, respectively. Depending on the different sphere locations, instantaneous and time averaged
vorticity data, scalar values of time-averaged velocity components and their root mean square (rms) values and
time averaged vorticity data are presented in the study for the evaluation of wake region of the spheres. It is
demonstrated that the gap between the two spheres and the interaction between the gap and the boundary layer
greatly affects flow pattern, especially when spheres are located near to the flat plate surface, i.e. S/D=0.1 for
0G/D 1.5. Different distances between the spheres resulted in various flow patterns as the spheres were
approached to the flat plate. The distance S/D=0.1 for all gap values has the strongest effect on the wake
structures. Beyond G/D=1.0, the sphere wakes tend to be similar to single sphere case. The instantaneous
vorticity fields of the side by side arrangements comprised wavy structures in higher level comparing to an
individual sphere case. The gap flow intensifies the occurrence of small scale eddies in the wake region. The
submersion rate of the spheres actually determines the characteristics of the wake region and is affected from
boundary layer flow in a gradually decreasing manner.