Microsoft Word-$ASQCopy of AIAA_2004-3928-Co-Flow-Cascade

International Journal of Turbomachinery, Propulsion and Power

This article provides a summarizing account of the results obtained in the current collaborative work of four research institutes concerning near-wall flow in turbomachinery. Specific questions regarding the influences of boundary layer development on blades and endwalls as well as loss mechanisms due to secondary flow are investigated. These address skewness, periodical distortion, wake interaction and heat transfer, among others. Several test rigs with modifiable configurations are used for the experimental investigations including an axial low speed compressor, an axial high-speed wind tunnel, and an axial low-speed turbine. Approved stationary and time resolving measurements techniques are applied in combination with custom hot-film sensor-arrays. The experiments are complemented by URANS simulations, and one group focusses on turbulence-resolving simulations to elucidate the specific impact of rotation. Juxtaposing and interlacing their results the four groups provide a broad p...

IX International Conference on Computational Heat and Mass Transfer, Cracow / Poland, 2016

The aim of this study is to investigate flow characteristics around open jet with different outlet area (circular, ellipse, triangle, square, rectangle, pentagon, hexagon) as experimental and numerically. Experimental studies were performed in air flow unit. Air velocity and turbulence measurements were carried out with hot wire probe which is module of multifunctional measurement equipment. CFD results were validated with the experimental values. The CFD’s results were found to agree well with actual values obtained as experimentally.

Volume 3: Heat Transfer; Electric Power; Industrial and Cogeneration, 2000

A flow modification technique is introduced in an attempt to allow increased turbine inlet temperatures. A large-scale two half-blade cascade simulator is used to model the secondary flow between two adjacent turbine blades. Various flow visualization techniques and measurements are used to verify that the test section replicates the flow of an actual turbine engine. Two techniques are employed to modify the endwall secondary flow, specifically the path of the passage vortex. Six endwall jets are installed at a location downstream of the saddle point near the leading edge of the pressure side blade. These wall jets are found to be ineffective in diverting the path of the passage vortex. The second technique utilizes a row of 12 endwall jets whose positions along the centerline of the passage are based on results from an optimized boundary layer fence. The row of jets successfully diverts the path of the passage vortex and decreases its effect on the suction side blade. This can be expected to increase the effectiveness of film cooling in that area. The row of jets increases the aerodynamic losses in the passage, however. Secondary flow measurements are presented showing the development of the endwall flow, both with and without modification.

Flat wall impingement cooling investigation was carried out using combined numerical analyses of conjugate heat transfer (CHT) and computational fluid dynamics (CFD) techniques. The analyses were undertaken in impingement array of jet holes with self-induced cross-flow in the impingement gap using a single sided flow exit geometrical model. The aim is to understand the aerodynamics interaction that results to the deterioration of heat transfer with axial distance, as the addition of duct flow heat transfer would be expected to lead to an increase in heat transfer with axial distance. A square array of impingement jet holes was used for a common geometry investigated experimentally, pitch to diameter ratio X/D of 5.0 and impingement gap to diameter ratio Z/D of 3.3 for 11 rows of holes in the cross-flow direction. A metal duct wall was used as the impingement surface with a 100 kW/m 2 imposed heat flux. For a gas turbine combustor cooling application operating at steady state with a temperature difference of ~ 450 K, this heat flux corresponds to a convective heat transfer coefficient (HTC) of ~ 200 W/m 2 K. A key feature of the predicted aerodynamics was recirculation in the plane of the impingement jets normal to the cross-flow, which produced heating of the impingement jet wall. This reverse flow jet was deflected by the cross-flow, which had its peak velocity in the plane between the high velocity impingement jets. The cross-flow interaction with the impingement jets reduced the interaction between the jets on the surface, with lower surface turbulence (TKE) as a result and this reduced the surface HTC. A significant feature of the predictions was the interaction of the cross-flow with the impingement jet wall and associated heat transfer to that wall. The results showed that the deterioration in heat transfer with axial distance was well predicted together with predictions of the impingement gap exit pressure loss.

Biomedical and Mechanical Engineering Journal (BIOMEJ)

The installation of elbow ducting in closed-loop wind tunnel installation will cause a pressure drop. Pressure drop was caused by flow separation and secondary flow phenomenon in the elbow ducting. The test section used in this experimental study was an octagonal elbow 90º with radius ratio (rm/Dh) = 0.6. Diameter hydraulic (Dh) elbow of 806 mm. In this study, the Reynolds number is measured based on the free flow velocity (U∞) inlet section, that is ReDh = 4.63x105. The experimental results showed the pressure drop is ΔCp = 1.46 for Re = 4.63x105. This difference in pressure value between the outer and inner (ΔCp) of the elbow ducting was caused by secondary flow. The secondary flow was observed through a horizontal velocity profile where at xi/Dh = 1.35, fluid flow was accelerated on the inner wall and decelerated on the outer wall of the ducting elbow. Then, at xi/Dh = 1.63 to xi/Dh = 2.01, there are gradual shifts of the velocity profile where the fluid flow is accelerated towar...

Journal of Flow Visualization and Image Processing, 2012

International Journal of Heat and Fluid Flow, 2020

In this paper, experimental investigation of the flow-field of a slot synthetic jet (SJ) with and without sidewalls, issuing into a quiescent environment is systematically reported. Two parallel sidewalls were mounted along the shorter side of the slot extending in the streamwise direction to constrain the flow along the slot span. Hot-wire anemometry was used to explore the flow-field characteristics of both configurations at a Reynolds number of 4000 based on the slot-width and slot average exit velocity during the ejection phase. The present work is a first step towards the investigation of the SJ flow-field characteristics in a bounded region. In a number of generic situations, this work is of high importance as the SJ is deployed in constrained environments (e.g., in cooling applications) where sidewalls may be present. The relative difference in the magnitude of the distinct peaks in the near-field spanwise velocity profiles for both configurations reveals that the vortex does not get curled up towards the centerline in the case of the synthetic jet with sidewalls due to the presence of the no-slip walls. Spectral analysis in the near-wall region further confirms the absence of the phenomenon of axis-switching in the case of the synthetic jet with sidewalls. This behavior is also demonstrated with the help of the relative spreading rate in both configurations, where the unbounded synthetic jet spreads rapidly compared to the bounded one, due to greater entrainment of the surrounding fluid. The statistically two-dimensional region for a synthetic jet with sidewalls is found to extend over a longer axial distance in the downstream. The other jet properties such as turbulence intensity, skewness, and flatness factors further reveal the differences in the flow-field of the two configurations. The results show that the presence of the sidewalls strongly influences the SJ flow-field and hence, it would significantly impact the heat transfer capacity of the SJ.

22nd Aerospace Sciences Meeting

In the frame of “engineering education” activities, the Laboratory of Fluid Mechanics and Turbomachinery (FMTULAB/ASPETE) is continuously targeting to create links between education and basic research activities in fluid mechanics/dynamics. This task is expected to attract and motivate young engineers and scientists to join the fluid dynamics sector, which significantly contributes to the improvement of efficiency of applications relating clean energy sources and air pollution control. For this purpose computational and experimental studies are combined mainly in fundamental topics, while innovative results are produced to improve the knowledge of additional effects rising from the adoption of alternative flow configurations. Axisymmetric jet flow constitutes a subject of research from the origins of fluid dynamics; however it remains a subject of interest due to the new findings regarding the influence of flow and geometry conditions utilized in configurations that diverge from the...

HVAC&R Research, 2014

This study presents numerical investigation of an air supply device based on wall confluent jets in a ventilated room. Confluent jets can be described as multiple round jets issuing from supply device apertures. The jets converge, merge, and combine at a certain distance downstream from the supply device and behave as a united jet, or so-called confluent jet. The numerical predictions of the velocity flow field of isothermal confluent jets with three Reynolds-averaged Navier-Stokes turbulence models (renormalization group k-ε, realizable k-ε, and shear stress transport k-ω) are reported in the present study. The results of the numerical predictions are verified with detailed experimental measurements by a hot wire anemometer and constant temperature anemometers for two airflow rates. The box method is used to provide the inlet boundary conditions. The study of the airflow distribution shows that a primary wall jet (wall confluent jet) exists close to the supply device along the wetted wall, and a secondary wall jet is created after the stagnation region along the floor. It is presented that the flow field of the primary and secondary wall jet predicted by turbulence models is in good agreement with the experimental data. The current study is also compared with the literature in terms of velocity decay and the spreading rate of the primary and secondary wall jet, the results of which are consistent with each other. Velocity decay and the spreading rate of the secondary wall jet in vertical and lateral directions were studied for different inlet airflow rates and inlet discharge heights. The comparative results demonstrate that the flow behavior is nearly independent of the inlet flow rate. Inlet discharge height is found to have impact close to the inlet, where the velocity decays faster when the jet discharges at higher level. The decay tendency is similar as the jet enters into the room for all discharge heights.

Heat and Mass Transfer, 2014

We propose in this work to study an isothermal and a non-isothermal laminar plane wall jet emerging in a coflow steam. The numerical solution of the governing equations was performed by a finite difference method. In this work, we are interested in the study of the influence of Grashof numbers on the wall jet emerging in a medium at rest. Further, we will examine the effect of the coflow stream on the behavior of the dynamic and thermal properties of the wall jet subjected to a constant temperature. A comparison with a simple wall jet is carried out. The results show that for a buoyant wall jet, two parameters can influence the flow: the inertial and buoyancy forces. The velocity effect indicates that the potential core length increases with the velocity ratio. We are also showed that when using a momentum length scale, the normalized longitudinal maximum velocity can reach an asymptotic curve at different velocity ratios. List of symbols b Ejection nozzle thickness (m) C p Specific heat at constant pressure of the fluid (J kg-1 k-1) Gr Grashof number [Gr = gbb 3 (T p-T ?)/v 2 ] h Local convection coefficient (w m-2 k-1) J Momentum discharged from the nozzle exit (J = u 0 2 b) (m 3 s-2) Nu Local Nusselt number (Nu = hx/k) Pr Prandtl number (P r = lC p /k) r Coflow velocity ratio (r = u co /u 0) Re Reynolds number (Re = u 0 b/v) Re x Local Reynolds number (Re x = um x /v) u, v Longitudinal and transverse components of the velocity, respectively (m s-1) u ex = uu co Longitudinal excess velocity (m s-1) x, y Longitudinal and transversal coordinate (m) y 0.5 Dynamic jet half-width, value of the lateral distance at which longitudinal velocity is half of the maximum value (m) Greek symbols q Fluid density (kg m-3) l Dynamic viscosity of the fluid (kg m-1 s-1) k Thermal conductivity of the fluid (w m-1 k) s p Wall shear stress s p ¼ l ou oy y¼0 ! , Pa t Fluid kinematic viscosity (l/q) (m 2 s-1) a Thermal diffusivity of the fluid (m/P r) (m 2 s-1) Subscripts p Wall value 0 Value at the jet exit

Experimental Thermal and Fluid Science, 2019

The triple jet in cross flow problem has been handled experimentally in the present work for its wide presence in several industrial and environmental applications. Different injection ratios and heights have been considered in the case of three inline inclined jets discharged in an oncoming cross flow generated within a wind tunnel. The jets were discharged from cylindrical ducts that were razed at different levels from the ground which gave rise to elliptic cross-sections characterized by a little and great diameters. Hot wire anemometry was used to ensure of the independence of the jet nozzles' location on the interacting flows' mixing while the particle image velocimetry technique was adopted to track the different jets' progression within the domain. The observation of the different extracted experimental data (velocity and vorticity vectors and contours, streamlines, jets' trajectories etc.) revealed the complementarity of the effect of the injection ratio and height. In fact, the augmentation of both parameters helped straighten the jets, decrease the pressure drop between the discharging nozzles, reduce the entrainment of the upstream jets and straighten their velocity trajectory. However and concerning the impact of the injection ratio that varied between , and , it was obvious that the intermediate value of , was critical as it corresponded to jets and mainstream with comparable forces that complicated furthermore their confrontation. The major vortices that were observed on the symmetry plane included the wake vortices that were most apparent for weaker injection ratios due to the pronounced reattachment to the tunnel ground. The second observable vortices in the symmetry plane are the leading edge vortices that develop at the upper periphery of the jets as a reaction to their entrainment of the mainstream, and that are most striking along the leading edge of the 1 st jet due to its most consistent deflection by the mainstream. jets in cross flow need even more attention and control than single jet models due to the multiplied level of complexity of the resulting flow field. In fact, on the one hand, there are more discharged jets that are bound to interact together, and on the other hand, all of them are going to confront an oncoming cross flow, even though at different intensity levels. In addition to the number of the involved jets, we have to consider further parameters that may be divided into two classes: geometric and flow variables. The geometric variables are expected to have second-order influence on the flow field mixing by affecting penetration and pressure drop across the jet. these parameters include injection port shape and flow injection angle [12] in addition to the different injection nozzles' shape, spacing, elevation and arrangement. As to the flow variables, they include the velocity ratio (first-order influence) and the density ratio (second-order influence) that may combine into the momentum flux ratio [12], in addition to the temperature difference between the jets and the mainstream.

Volume 1: Turbomachinery, 1986

A detailed experimental investigation of the three-dimensional subsonic flow was carried out in a typical nozzle and impulse configuration of plane turbine cascades with a chord length 0.5 m. Flow parameters were measured within the passage and behind the cascade using a five-hole probe. Pressure distribution measurements and flow visualization were made on blade surfaces and side walls. Flow measurements were taken in endwall and airfoil boundary layers for both types of cascades. The influence of the aspect ratio, the inlet side wall boundary layer and the position of traversing planes on aerodynamic characteristics and losses is discussed.

In the present paper an extensive study of rectangular cross-sectioned C-duct and C-diffuser is made by the help of 2-D mean velocity contours. Study of flow characteristics through constant area duct is a fundamental research area of basic fluid mechanics since the concepts of potential flow and frictional losses in conduit flow were established. C-ducts are used in aircraft intakes, combustors, internal cooling systems of gas turbines, ventilation ducts, wind tunnels etc., while diffuser is mechanical device usually made in the form of a gradual conical expander intended to raise the static pressure of the fluid flowing through it. Flow through curved ducts is more complex compared to straight duct due to the curvature of the duct axis and centrifugal forces are induced on the flowing fluid resulting in the development of secondary motion (normal to the primary flow direction) which is manifested in the form of a pair of contra-rotating vortices. For a diffuser in addition to the secondary flow, the diverging flow passage, which causes an adverse stream wise pressure gradient, can lead to flow separation. The combined effect may result n non uniformity of total pressure and total pressure loss at the exit. A comparative study of different turbulent models available in the Fluent using y  as guidance in selecting the appropriate grid configuration and turbulence models are done. Standard k-ε model and RSM models are used to solve the closure problem for both the constant area duct and the diffuser. It has been observed that the Standard k-e model predicts the flow through the constant area duct and the diffuser within a reasonable domain of the y  range.

Experiments in Fluids, 2015

List of symbols c Coolant upstream of impingement plate C ax Axial chord length D Hole diameter H Impingement gap height M Blowing ratio (ρ c U c /ρ ∞ U ∞) Ma Mach number P Pressure PIV Particle image velocimetry p Pitch length Re Reynolds number (ρ ∞ U ∞ C ax /μ ∞) S Blade span s Static or streamwise coordinate T Temperature tke Turbulent kinetic energy 3/4 u ′ 2 + v ′ 2 U Velocity U inviscid Average inviscid velocity vector U meas Average measured velocity vector U sec Secondary velocity vector (U meas − U inviscid) u ′ Fluctuating velocity x Blade axial coordinate y Blade pitchwise coordinate z Blade spanwise coordinate δ Boundary layer thickness (99 %) μ Dynamic viscosity ρ Density ∞ Mainstream conditions at the cascade inlet