Particle image velocimetry (PIV)

The single dielectric barrier discharge plasma actuators (PAs) are known to be effective for flow control process. This study investigated the winglet-type thin and small PAs, which were suspended in the quiescent air flow. We conducted the PIV measurements and flow computations for the PA induced flow. The induced flow was discussed on three regions: a sink-like flow to the electrode, a shear flow over the winglet surface, and a jet-like flow downstream from the winglet. When the electrode
was located at the leading edge of the winglet PA, the sink-like flow was effectively enhanced. On the other hand, when the electrode was located at the trailing edge, the friction loss was minimized for the near-wall high shear flow over the winglet, and thus the highest momentum integral was obtained for the downstream jet-like flow. From these results, the most effective flow actuation was suggested to be achieved by the short winglet that had the exposed electrode at a leading edge and the covered
electrode at a trailing edge.

Detailed flow patterns and turbulence parameters, including secondary-flow mean velocity vector, turbulent intensity, Reynolds stress and turbulent kinetic energy, are compared between three different rib orientations (45-deg,-45-deg, and 90-deg) in a two-pass ribbed-wall parallelogram channel with a 180-deg sharp turn. Velocity measurements were performed with Particle Image Velocimetry (PIV). The channel has a cross-sectional equal length, 45.5 mm, of adjacent sides and two pairs of opposite angles are 45-deg and 135-deg. The rib height-to-hydraulic diameter ratio and pitch-to-height ratio were 0.1 and 10, respectively. All the measurements were performed at a fixed Reynolds number, characterized by channel hydraulic diameter of 32.17 mm, cross-sectional bulk mean velocity, and fluid property of air at room temperature, of 10,000 and a null rotating number. A correlation between pitchwise variations of the reattachment lengths and rib-edge normal mean velocities is found. In addition, a comparison of the spanwise reattachment loci in the present parallelogram channel with those reported previously in the square channels is made. Overall, the 45-deg ribs and-45-deg or 90-deg ribs augment the secondary flow motion most in the first and second pass, respectively. Among the rib orientations investigated, the 45-deg and-45-deg ribs induce a pair of counter-rotating longitudinal vortices that strengthens the inlet-generated secondary flow in the first pass and the 180-deg sharp turn generated secondary flow in the second pass, respectively. One interesting finding is the noticeable difference in the flow characteristics near the top and bottom walls of the parallelogram channel for all three rib angles examined. On the contrary, previous studies with the square channels revealed almost the same heat transfer distributions on the 45-deg ribbed top and bottom walls.

An investigation has been undertaken into the blockage and wake characteristics of various scaled Savonius turbines.  The Savonius turbine is a vertical axis turbine which can be utilised in either an aero or hydro environment; however, this study will focus on the Savonius turbine in the water environment.  Many studies have been compiled which examine the performance characteristics of the turbine in a closed test section in a laboratory flume, with the aim to improve design efficiency, power output etc.  Blockage effects result in local flow acceleration on either side of the turbine due to the constriction caused by the flume walls in relation to the turbine scale. This phenomenon is absent when the turbine is placed unobstructed in an open marine scenario (i.e. no side wall effects).  Since the power output of a turbine is proportional to the cube of the inflow velocity, the inability to quantify the blockage effect can lead to an over-estimation of the performance of a turbine in the laboratory environment.  This study aims to use the non-intrusive particle image velocimetry (PIV) technique to obtain the time averaged flow field surrounding four various scaled Savonius turbines at two different azimuth angles 0 and 90, representing different degrees of blockage.  The PIV analysis was performed in 2D, on a horizontal plane at the mid-depth of the flow and turbine.  Wake characteristics of the various scaled turbines were examined and compared.  The study revealed that an increase in blockage factor results in a decrease in the length of the turbine wake.  The turbine with the smallest blockage factor of 20% at 0 and 90deg resulted in wake lengths X/D = 13.4 and 20.4, whilst the turbine with the largest blockage factor of 50% at 0 and 90deg resulted in wake length X/D = 4.22 and 3.055, respectively.

Particle image velocimetry (PIV) can be used for pressure assessment. This non intrusive measurement method provide a high spatial resolution which is unavailable when using pressure transducers. The velocity vector information was used to solve inversely the Navier-Stokes equation to provide the pressure gradient needed for the Neumann boundary condition. Then the velocity data was used again to solve the pressure Poisson equation. Two flow problems were tested, water flow in a pipe with a constriction and an impinging air jet. The constriction flow was chosen to represent laminar flow problem where pressure is changing significantly. Results were compared with an inviscid solution. and the effect of spatial resolution was examined. The impinging air jet was chosen to represent a turbulent flow problem. The pressure distribution on the impingement plate was compared with reported data from the literature and some aspects of time averaging were discussed. and turbulent flows. The pressure field in both laminar and turbulent flows is useful when forces are to calculated, when comparison with pressure gauging is required, and when better understanding of the flow problem is desired. Pressure gauges used for pressure measurement are expansive, large in their size, and require an actual contact with the fluid. When the measurement is performed intrusively the flow and pressure are affected by the procedure itself (e.g. while using a catheter for coronary procedures). It was suggested, therefore, to avoid such difficulties by computing the pressure field from the velocity data generated by the non intrusive particle image velocimetry method. In the current study we present calculation results of pressure fields based on the instantaneous velocity fields obtained by particle image velocimetry.

Schlieren imaging or imaging through inhomogeneous transparent media  was previously used for qualitatively visualising fluid flow field . Recent development in the computerised mathematical techniques and image based data extraction has enabled quantitative measurement of desired parameters with the help of various interfaces, used defined sub-routines. An overview to the schlieren imaging literature is presented from the era of origin till date which . This article also describes a step by step procedure to extract density field of a flow field by Background oriented schlieren (BOS) technique/Synthetic Schlieren(SS)/ Tomographic image Reconstruction Technique.

The second log-wake law is a small change of the first log-wake law (or Coles' log-wake law) for turbulent pipe and symmetric channel flows but makes a big difference in modeling wall-bounded turbulent flows. It has been extended to antisymmetric Couette channel flows theoretically and open channel flows empirically. A recent study of natural river flows indicates that a river velocity distribution is a superposition of a complete antisymmetric channel flow solution due to water surface shear stress and a half symmetric channel flow solution due to gravity. The objective of this research then is to test this hypothesis under the effects of ice cover and wind-induced water surface shear stress with laboratory experiments. To this end, a special experimental device was designed to simulate the effects of gravity, ice cover, and wind-induced shear stress. With this device, 236 vertical distributions of streamwise velocity were measured with a particle image velocimetry (PIV) technique under various simulated conditions of ice cover and water surface shear stress, 75 of which are plotted in this paper. All measured velocity distributions are characterized by a bowl-shaped velocity distribution with a dip phenomenon, a typical boundary layer velocity distribution, or an S-shaped velocity distribution with an inflection. All of these three distribution patterns are well described by the second log-wake law, which also agrees with real-world river flow data. Based on the second log-wake law, an innovative three-point method is proposed for river discharge measurements.

The single dielectric barrier discharge plasma actuators (PAs) are known to be effective for flow control process. This study investigated the winglet-type thin and small PAs, which were suspended in the quiescent air flow. We conducted the PIV measurements and flow computations for the PA induced flow. The induced flow was discussed on three regions: a sink-like flow to the electrode, a shear flow over the winglet surface, and a jet-like flow downstream from the winglet. When the electrode
was located at the leading edge of the winglet PA, the sink-like flow was effectively enhanced. On the other hand, when the electrode was located at the trailing edge, the friction loss was minimized for the near-wall high shear flow over the winglet, and thus the highest momentum integral was obtained for the downstream jet-like flow. From these results, the most effective flow actuation was suggested to be achieved by the short winglet that had the exposed electrode at a leading edge and the covered
electrode at a trailing edge.

"This thesis details the development, verification and validation of an unsteady unstructured high order (≥ 3) h/p Discontinuous Galerkin - Fourier solver for the incompressible Navier-Stokes equations on static and rotating meshes in two and three dimensions. This general purpose solver is used to provide insight into cross-flow (wind or tidal) turbine physical phenomena.
Simulation of this type of turbine for renewable energy generation needs to account for the rotational motion of the blades with respect to the fixed environment. This rotational motion implies azimuthal changes in blade aero/hydro-dynamics that result in complex flow phenomena such as stalled flows, vortex shedding and blade-vortex interactions. Simulation of these flow features necessitates the use of a high order code exhibiting low numerical errors. This thesis presents the development of such a high order solver, which has been conceived and implemented from scratch by the author during his doctoral work.

To account for the relative mesh motion, the incompressible Navier-Stokes equations are written in arbitrary Lagrangian-Eulerian form and a non-conformal Discontinuous Galerkin (DG) formulation (i.e. Symmetric Interior Penalty Galerkin) is used for spatial discretisation. The DG method, together with a novel sliding mesh technique, allows direct linking of rotating and static meshes through the numerical fluxes. This technique shows spectral accuracy and no degradation of temporal convergence rates if rotational motion is applied to a region of the mesh. In addition, analytical mappings are introduced to account for curved external boundaries representing circular shapes and NACA foils.

To simulate 3D flows, the 2D DG solver is parallelised and extended using Fourier series. This extension allows for laminar and turbulent regimes to be simulated through Direct Numerical Simulation and Large Eddy Simulation (LES) type approaches. Two LES methodologies are proposed.

Various 2D and 3D cases are presented for laminar and turbulent regimes. Among others, solutions for: Stokes flows, the Taylor vortex problem, flows around square and circular cylinders, flows around static and rotating NACA foils and flows through rotating cross-flow turbines, are presented."

The book begins with a review of three-dimensional Particle Image Velocimetry (PIV). PIV has become a standard technique over recent decades, and is useful for studies in which an optically clear fluid can be seeded with small, neutrally buoyant particles. Applications have included shipping and aircraft design, and simulation of cardiovascular flow dynamics. Stereo PIV is a more recent extension that requires additional care in establishing the flow, selecting the equipment, aligning the optics, calibrating the images, and choosing appropriate data analysis methods. The information in this first chapter is expected to be a practical guide to anyone who is interested in using this method or in purchasing the equipment necessary to do so.

Resuspension of solid particles by a tornado-like vortex from surfaces of different roughness is studied using a three-dimensional particle tracking velocimetry (3D-PTV) method. By utilizing the three-dimensional information on particle positions, velocities and accelerations before, during and after the resuspension (lift-off) event, we demonstrate that the resuspension efficiency is significantly higher from the rough surface, and propose a mechanistic model of this peculiar effect. The results indicate that for all Reynolds numbers tested, the resuspension rate, as well as particle velocities and accelerations, are higher over the rough surface, as compared to the smooth counterpart. The results and the model can help to improve modeling and analysis of resuspension rates in engineering and environmental applications.

Particle image velocimetry was used in a low-speed wind tunnel to investigate the vortex structures of a slender reverse delta wing at various angles of attack and roll. This work investigates the characteristics of the vortices generated downstream in planes perpendicular to the freestream direction and their dependence on angles of attack and roll at a chord-based Reynolds number of Re c 3:82 10 5 . The peak tangential velocities at > 5 show a trend similar to a delta wing. A six-component balance was used to obtain the aerodynamic coefficients for a reverse delta wing as well as a delta wing for comparison. A simulation of the streamlines, velocity vectors, and surface pressure contours was carried out using computational fluid dynamics software to show the characteristics of the flow over a reverse delta wing.

For more than a century, there has been much debate around the use of telekinesis-psychokinesis (TK ) to explain the rotating movement of light objects on an upright standing needle in the proximity of a hand. Thermally-induced aerodynamic effects have been considered as likely physical explanation factors. Despite this controversy, many still upload videos claiming the phenomenon on the internet. Most of the scientific studies performed were focused on whether or not the effects could be observed if some physical constraints were added, in order to avoid the aerodynamics factor, or if  the same results could be reproduced using some thermic or/and aerodynamic artefacts instead of a human presence. The first approach runs the risk of inhibiting a phenomenon about which little is known. The second has not yet shown clear reproducible experiences, which produce the same results as with a human presence, except in very specific situations.
Our objective is to be able to detect and study psychokinesis in confined and non-confined environments with scientific measurement tools. Our hypothesis is that there could be a way to separate psychokinetic effects from aerodynamic effects, even in a non-confined environment, so avoiding the drawbacks of the first approach. This technique of approaching anomalous perturbations could be described as partial physical isolation of the target system, with a measurement system ensuring control of the remaining known effects. It can be related to two other techniques previously described (May, Uttis & Spottiswoode 1995: Introduction).
From the beginning, the LAPDC has been fostering a PKers (subjects practicing psychokinesis) volunteer team in order to do the experiments. From 2012 to 2016, we have been developing specific scientific methods in order to study the psychokinesis effect on a spinning mobile with or without confinement. More specifically, we developed a protocol starting with particle image velocimetry (PIV) in order to measure the air-flow speeds around the mobile. Further research has driven us to create a set of processes using MATLAB, which we named Scan-Flow-Mobile. It has enabled us to construct one global model, integrating air flow movements and mobile movements, and scrutinize it. Using this, we were able to compare different experiments. We conducted a thorough analysis of the interaction between the mobile and the air flows, and studied the cause-and-effect relationships between their movements.
A review of the “spinning mobiles” literature of the last century, either with psychokinetic hypothesis and aerodynamic/thermic explanation, has been done. We also studied other potential causes of motion such as electrostatic forces, magnetism, vibrations, and the impact of radiation. Then, as a pilot study, we conducted eight experiments in non-confined environments, with three set-up categories: one where the mobile motion was driven by generated air flows (A), one in which a motor drove the mobile (M) and the last one where a PKer drove the mobile (PK). The ratio (mobile speed/mobile periphery airflow speed) was used as a way to compare experiences between experiments and categories. In this paper we focus only on the methodological approach and so on the categories A and M. With regard to this ratio, the category M experiments stayed above or equal to two, while category A was below or equal to 0.5. This separated clearly pure aerodynamic effects (A) from the motor driven effect (M). So the methodology could be a good candidate to conduct macro-PK test in a non-confined environment with the capability to eliminate or not the aerodynamic effect as explanation.  A potential bias and errors analysis is presented, which takes into account the difference between air-flow and smoke-particle velocity, the mean speed evaluation for the air flows and the mobile. Indeed, we evaluated the potential error on the ratio air-flow speed/mobile speed as approximately +/- 8.9%, which is marginal compared to the ratios differences between categories A and M.
The methodology presents also some features that helps detect tricks that could be tried by some misbehavioring PKer (as mouth air blowing, hand move...).
We’ll look to improve the total measurement process documentation, in order to give other laboratories the possibility to test it in their experiments.

“Reprinted from “[A Methodology Proposal for Conducting a Macro-PK Test on Light Spinning Objects, in a Non-Confined Environment]”, Journal of Scientific Exploration, vol. [32], no. [3], pp. [514], published by the Society for Scientific Exploration, https://www.scientificexploration.org.”

Resuspension of solid particles by a tornado-like vortex from surfaces of different roughness is studied using a three-dimensional particle tracking velocimetry (3D-PTV) method. By utilizing the three-dimensional information on particle positions, velocities and accelerations before, during and after the resuspension (lift-off) event, we demonstrate that the resuspension efficiency is significantly higher from the rough surface, and propose a mechanistic model of this peculiar effect. The results indicate that for all Reynolds numbers tested, the resuspension rate, as well as particle velocities and accelerations, are higher over the rough surface, as compared to the smooth counterpart. The results and the model can help to improve modeling and analysis of resuspension rates in engineering and environmental applications.

The measurement and prediction of the aerodynamic performance of airfoils and wings at chord Reynolds numbers below 10 5 are both difficult and increasingly important in the application to small-scale aircraft. Not only are the aerodynamics strongly affected by the dynamics of the unstable laminar boundary layer, but the flow is decreasingly likely to be two-dimensional as the Reynolds number decreases. The spanwise variation of the nominally two-dimensional flow along a two-dimensional geometry is often held to be responsible for the large variations in the measured profile drag coefficient c d at this scale. Here, local two-dimensional drag coefficients are measured along a finite wing using nonintrusive particle image velocimetry methods. Variations in c d y can be related to local flow variations on the wing itself. Integrated values can then be compared with direct force balance data, and the dynamical significance of spanwise variability will be reevaluated.

Flow of liquid over a weir is important in a variety of contexts and has been productively studied for a number of
decades. Granular !ow over a blade (or weir) is essential for mixing operations in various industries but has not
been studied to the same extent as in liquid systems.We have carried out experiments to study the velocity "eld
and mixing of granular material as it !ows over a single blade. We observe that like in !uids it is possible to have
material !owagainst themain !owdirection, leading to a recirculation region in front of the blade/weir. However
unlike in !uid !owswe observe that such a recirculation can occur for granular !ows if the Froude number is less
than a critical Froude number, i.e., for subcritical !ows. We study the !ow by varying the particle size and bed
height and we characterize the results based on the Froude number and a dimensionless shear rate. Mixing is
quanti"ed using a dispersion coef"cient and we "nd that our results agree qualitatively with a simple model
for granular mixing. Finally we examine the mixing behavior when moisture is added to the grains and observe
an increase in the mixing rate compared to dry !ows.

Each geomorphic hazard involves a degree of risk which incorporates quantification of the probability
that a hazard will be harmful. At present, the categorization of sub-watersheds into erosion risk is considered
as the fundamental step to conserve the soil loss. Development of badlands over the laterites of
Birbhum district is an indicative of excessive soil loss in the monsoonal wet-dry type of climate. Slope
erosion and channel erosion have generated huge amount of sediment from the small watersheds during
intense monsoonal rainfall (June–September). The adjoining areas of Rampurhat I Block, Birbhum
(West Bengal) and Shikaripara Block, Dumka (Jharkhand) have lost the lateritic soil cover at a rate of
20–40 ton/ha/year (Sarkar et al. 2005). In order to estimate the progressive removal of soil particles from
the gully-catchments of the above-mentioned area, different morphometric parameters, soil parameters,
hydrologic parameters and empirical models are employed. Side by side, the study is carried out to categorize
the gully-catchments into different magnitude of erosion risk using several multivariate statistical
techniques.

This paper demonstrates a strategy to integrate research into teaching at a postgraduate level. It involves the
use of simple small-scale physical models of a tunnel heading, the introduction of particle image velocimetry, an
advanced computing technique used to further visualize the movement of soil, and a numerical model of a tunnel
heading. Based on staff experience and student feedback, it is concluded that this is an effective and satisfying
way to engage students with the subject matter. It is also hoped that discussing and displaying some of these
advanced topics will encourage further student interest in geotechnical engineering research.

A model of magma propagation in the crust is presented using a series of analogue experiments, where dyed water is injected at a constant flux into layers of solidified gelatine. The gelatine layers are transparent and, when intruded, deform in an almost ideal-elastic manner under the experimental conditions (low gelatine concentration: 2.5 or 3 wt%, and low temperature: 5–10◦C). The upper gelatine layer was 1.0 to 1.5 times stiffer than the lower layer, with either a ‘weak’ or ‘strong’ interface strength between the gelatine layers. The gelatine is seeded with 20–50μm-diameter PMMA-RhB neutrally buoyant particles that are fluoresced by a pulsed, vertical laser sheet centred on the injection point. Digital image correlation (DIC) is used to calculate incremental strain and finite strain in the deforming host material as it is intruded. This is mapped in 2D for the developing experimental volcanic plumbing system that comprises a feeder dyke and sill. Since the gelatine deforms elastically, strain measurements correlate with stress. Our results indicate that, for constant magma flux, the moment of sill inception is characterised by a significant magmatic pressure decrease of up to ∼60%. This is evidenced by the rapid contraction of the feeder dyke at the moment the sill forms. Sill propagation is then controlled by the fracture properties of the weak interface, with fluid from the feeder dyke extracted to help grow the sill. Pressure drops during sill inception and growth are likely to be important in volcanic systems, where destabilisation of the magmatic plumbing system could trigger an eruption.

A numerical algorithm for the simulation of flow past immersed objects with heat transfer is proposed and validated which conforms with the ideas of the fictitious domain method. A momentum source term is added to account for the presence of the object and a heat source term is proposed to impose the Dirichlet boundary condition on the surface of the objects. The algorithm is an implicit fictitious domain based method where the entire fluid-immersed object domain assumed to be an incompressible fluid. The flow domain is constrained to be divergence free, whereas a rigidity constraint is imposed on the body domain. Heat transfer is similarly considered by assuming that the object domain is filled with a fluid with different thermal properties. The SIMPLE algorithm with a collocated grid arrangement is used for pressure–velocity coupling which is unconditionally stable. The algorithm is validated by considering stationary, forced motion and freely moving objects with both isothermal and freely variable temperature inside the object. Good agreement with previous numerical and experimental studies for all the test cases is observed.

Supersonic turbulent flows in a rectangular duct are characterized by secondary flows in each of the four corners of the duct. These secondary flows comprise of two counter rotating vortices forcing the fluid towards the corner. The vortices are developed as a result of the Reynolds stress gradients which exist in each of the corners. Previous studies 1,2 have primarily used intrusive techniques such as Preston/pitot tubes and hot wire in order to study the secondary flows in the corners. However use of these techniques would substantially modify the flow in low aspect ratio rectangular channels. Thus, there is a need for non-intrusive measurements to study the evolution of corner vortices in such flows. In this study we present the experimental results of stereo particle image velocimetry conducted on a Mach 2.75 flow in a low aspect ratio rectangular channel. Data is recorded at multiple cross-section planes and analyzed to study the formation of corner vortices and their effects on the structure of the mean flow field. Results show that the corner vortices are formed in the corner and then convect away from it. There is a significantly strong secondary flow associated with the corner vortices possibly causing open flow separation. The vortices significantly modify the local variation of the skin friction coefficient.

In this work, time-resolved particle image velocimetry (TR-PIV) measurements have been carried out to study the flow structure and flow dynamics of submerged transverse impinging twin-jet flows discharged into a confined laminar crossflow. A parametric study has been carried out for fixed spacing ratio between the jets of 𝑠 = 𝐿∕𝐷 = 3, fixed jet-to-target spacing ratio of 𝐻∕𝐷 = 6.73, fixed crossflow Reynolds number of 𝑅𝑒 = 3500, and two jet Reynolds numbers based on the outlet velocities and jet diameter 𝐷 of 𝑅𝑒𝑗 = 8670 and 9933 that correspond to jet-to-cross-flow velocity ratios of 𝑟 = 𝑣𝑗∕𝑢0 = 10 and 11.46, respectively. Flow measurements in several different planes of the test section are acquired to assess the confinement effect of the bounded jets. Flow visualization images of the mean velocity, vorticity, strain rate distributions, turbulence kinetic energy, and Reynolds stresses have been obtained. The results reveal the dependence of 𝑅𝑒𝑗 on the trajectory, penetration, crossflow entrainment and lateral spreading of the twin jets. Spectral analysis of the fluctuating velocity components shows the characteristic frequencies related to vortex pairing and vortex breakup, and the shedding frequencies of the upstream and downstream wall jets have also been obtained. The swirling strength criteria has been applied to identify coherent structures, and their development confirms that these structures undergo two or three stages of vortex pairing prior to the vortex breakdown activity. The experimental data has been analyzed using proper orthogonal decomposition (POD), and the most energetic modes, the relative and cumulative energy contributions, dominant POD modes, and temporal POD coefficients have been obtained. The results show that the for 𝑅𝑒𝑗 = 8670, the first two POD modes account for 16.50% of the total kinetic energy, and the cumulative energy of the first 20 POD modes is 55.10%. For 𝑅𝑒𝑗 = 9933, the first two POD modes account for 17.98% of the total energy, and the sum of energies of the first 20 POD modes is 57.13%.

A parallelogram channel has drawn very little or no attention in the open literature although it appears as a cross-sectional configuration of some gas turbine rotor blades. Particle image velocimetry (PIV) is presented of local flow structure in a two-pass 90 deg ribbed-wall parallelogram channel with a 180 deg sharp turn. The channel has a cross-sectional equal length, 45.5 mm, of adjacent sides and two pairs of opposite angles are 45 deg and 135 deg. The rib height to channel height ratio is 0.1. All the measurements were performed at a fixed Reynolds number, characterized by channel hydraulic diameter of 32.17 mm and cross-sectional bulk mean velocity, of 10,000 and a null rotating number. Results are discussed in terms of the distributions of streamwise and secondary-flow mean velocity vector, turbulent intensity, Reynolds stress, and turbulent kinetic energy of the cooling air. It is found that the flow is not periodically fully developed in pitchwise direction through the inline 90 deg ribbed straight inlet and outlet leg. Pitchwise variation of reattachment length is revealed, and comparison with reported values in square channels is made. Whether the 180 deg sharp turn induced separation bubble exists in the ribbed parallelogram channel is also documented. Moreover, the measured secondary flow results inside the turn are successively used to explain previous heat transfer trends. Keywords: PIV, 90 deg ribbed two-pass parallelogram channel, turbulence anisotropy, relationship between fluid flow and wall heat transfer

A six component force balance was used to obtain the C L for a reverse delta wing and a delta wing for comparison purposes. A simulation of the streamlines, velocity vectors and surface pressure contours was carried out using CFD software to show the characteristics of the flow over a reverse delta wing.

The experience gained during the development of a small turbojet engine simulation model is presented in this paper. The calibration of an initial model has been proven inadequate for producing reasonable values for some performance parameters, such as the turbine efficiency. Data analysis procedures indicated that some measurements were not thermodynamically consistent. Model recalibration based on the use of static instead of total pressure measurements in the turbine exit has proven to be beneficial both for the prediction of the measured parameters and for producing reasonable values for the turbine efficiency. Data correction procedures were also implemented successfully in order to incorporate all the available measurements in the model.

The significance of the acceleration zone is expressed when designing a straight pipeline that follows either thefeeding point or a bend in a pneumatic conveying system. It is an effective and reliable system that takes into ac-count the acceleration zone in the design process. The current paper presents a thorough experimental investi-gation of particle velocity profile at the acceleration region obtained from 3-in, 2-in and 1-in horizontal dilutephase pneumatic conveying systems with various operating conditions and conveyed materials. The velocitywas obtained by using a high speed camera combined with image processing. Investigation of the statistical ve-locity distribution resulted in a new correlation for the particle velocity profile throughout the acceleration zoneand the acceleration length in the range of the tested operating conditions.

Quad/tri-copters, and small scale fixed wing aircrafts (as small as 15cm) are currently in use over a wide range of applications. However, the uses of avian based flapping MAVs have not yet been fully exploited. Flapping wing MAVs have considerable advantages over rotorcrafts in the areas of agility and stealth hence the design of aerodynamically efficient MAVs is important. At this scale the flapping wing MAV will operate within a low Reynolds number range of 10 4 -10 5 . This produces complex aerodynamic behavior with highly vortical flow, separated flow, and complex wake structures. Consequently, the aerodynamic behavior is particularly sensitive to changes in free stream conditions and wing kinematics; hence it is difficult to model fluid mechanics and performance predictions for lift and drag. One of the main vortical flow structures is the Leading Edge Vortex (LEV). This is responsible for the lift characteristics of flapping wings. The other major vortical structure is the Tip Vortex (TV). As with fixed wing aircrafts, this vortex creates vortex drag, which reduces the efficiency of the lift and drag parameters of the wing. These tip vortices will be studied on rigid wings via Computational Fluid Dynamics (CFD) to quantify its chordwise evolution and strength, and to understand how it affects vertical and propulsive force generation by flapping in forward flight within steady free stream conditions. Solution files were produced using a CFD solver (OVERTURNS) and were then exported to Tecplot 360 to extract slices of data at specific points along the chord of the wing. Vorticity contours were used to visualize wingtip vortices, and to create vortex swirl profiles. Quantifying the characteristics of the TV will help to understand its impact on the flight performance of the flapping wing MAV. Consequently, this will lead to understanding and controlling the TV through wing kinematics and/or wing geometry for improved flight efficiency.

KEY POINTS:  The velocity fields induced by regular breaking waves past a fixed bar on a 1:10 rigid plane slope were measured and analysed using a volumetric particle-tracking velocimetry system.  The linear momentum is generally positive during breaking (transfer toward the crest) and negative immediately after breaking (transfer from the crest toward the underlying flow field).  The average pressure gradient during breaking influences the profile of the breaker.

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 different flow structures
in the recirculation region for the presence of the spoiler. The foci and the saddle point,
appearing in the wake, form differently along the streamwise direction. The recirculation zone
with the spoiler is longer and narrower than without the spoiler. Moreover, the spoiler
installed on the vehicle diminishes peak magnitudes of the flow characteristics and thus it is
expected that the flow-induced forces will be lessened which contributes to the driving
stability.

Particle image velocimetry (PIV) measurements are carried out in an experimental investigation of laminar opposing mixed convection to assess the thermal effects on the wake of an isothermal circular cylinder placed horizontally and confined inside a vertical closed-loop downward rectangular water
channel. The buoyancy effect on the flow distributions are revealed for flow conditions with Reynolds number based on cylinder diameter of Re = 170, blockage ratio, D/H = 0.287, aspect ratio, L/D = 6.97 and values of the buoyancy parameter (Richardson number) in the range 1 6 Ri 6 5. In this work, flow
distributions are presented in the form of mean and instantaneous contours of velocity and vorticity. To elucidate the effects of the lateral wall proximity effect and cylinder aspect ratio, separation angle, wake structure behind the cylinder, recirculation bubble length, time traces of velocity fluctuation, Strouhal number and vortex shedding modes are obtained as a function of the Richardson number. The results
reported herein demonstrate how the flow structure and vortex shedding pattern are significantly modified by the wall confinement and thermal effects. In addition, our measurements show that for assisted buoyancy (Ri = 1), the breakdown of the Kármán vortex street takes place and vortex shedding is completely suppressed.

Turbulent flows are often treated as a noisy environment by control algorithms of underwater robots. However, aquatic animals such as fish have learned to take advantage of certain unsteady flow. Periodic complex flow, such as that found in the wake of cylinders has been shown to offer energy saving opportunities to fish. We built a fish-like robot with an integrated pressure sensor array housed in the head. The robot can control its tail beat synchronization with respect to the periodic oscillations in the flow behind a cylinder. We show that vortices, represented here by pressure maxima, can be detected and exploited to increase the swimming efficiency of the robot fish while it remains rigidly mounted to a force plate. Force measurements show an efficiency gain of 23% when the tail beat of the robotic fish is synchronized at a particular phase lag.

Experimental investigation of the effect of initial soil parameters to formation of failure surface geometry behind retaining walls for granular soils is seldom attempted in literature. Only recently there are model studies that attempt to evaluate the influence of initial sand density on shear band characteristics. However, in these studies, model setups lack the capability to vary the stress state. Therefore, influence of stress state on strain localization cannot be monitored and the only influence on localization is soil density. Accordingly, this study presents the results of retaining wall physical model tests with granular backfills on which a controlled surcharge can be imposed. In this way, the combined influences of stress state and relative density on the distribution of strains within the backfill are investigated using particle image velocimetry method. This paper presents the preliminary experimental results and discusses the influence of preshear soil properties on shear band geometry for retaining walls translating laterally.

Stepped spillways have higher energy dissipation than smoother hydraulic structures used to divert flood discharges. The inception point related to air entrainment is however located further upstream. The air entrainment causes an undesired bulking of the flow depth. For large discharge rates and for straight stepped spillways, the skimming flow regime may be assumed two-dimensional. This is an attractive feature for the application of non-intrusive flow visualisation techniques because these methods measure the flow characteristics in the vicinity of the sidewalls which are likely to correlate to the flow at the centre of the flume. This paper tests the hypothesis that such techniques can be used to measure the flow inside the flume. The hypothesis is tested against measurements taken with an intrusive probe. Void fraction contour lines and velocity fields are obtained in 12 different stepped spillway configurations using the Image Processing Procedure (IPP) and the Bubble Image Velocimetry (BIV) respectively. The void fraction and velocity results are overall consistent with the probe measurements. The velocity fields show a persistent underestimation of the probe measurements which can at least be partially explained by sidewall effects and possible probe’s overestimation.

3D-PIV and 2D-LDA measurements in a fully turbulent boundary with adverse pressure gradient have been performed. Two types of surfaces were investigated: a smooth surface and a surface with riblets aligned in main flow direction. Particle image velocimetry was used to determine the influence of the surface structure on large-scale structures in the near wall region whereas profiles of mean and fluctuating velocity inside the boundary layer were acquired by laser Doppler anemometry. Significant changes of size and location of near-wall vortex structures were found ongoing with a deformation of the mean-velocity profile due to the riblet surface.

Researchers at the International Hurricane Research Center (IHRC), Florida International University (FIU), are working in stages on the construction of a large state-of-the-art Wall of Wind (WoW) facility to support research in the area of Wind Engineering. In this paper, the challenges of simulating hurricane winds for the WoW are presented and investigated based on a scale model study. Three wind profiles were simulated using airfoils, and/or adjustable planks mechanism with and without grids. Evaluations of flow characteristics were performed in order to enhance the WoW's flow simulation capabilities. Characteristics of the simulated wind fields are compared to the results obtained from a study using computational fluid dynamics (CFD) and also validated via pressure measurements on small-scale models of the Silsoe cube building. Optimal scale of the test model and its optimal distance from the WoW contraction exit are determined - which are two important aspects for testing using an open jet facility such as the WoW. The main objective of this study is to further the understanding of the WoW capabilities and the characteristics of its test section by means of intensive tests and validations at small scale in order to apply this knowledge to the design of the full-scale WoW and for future wind engineering testing.

The flow characteristics in the inertial Reynolds number regime are investigated in a mono-dispersed random pack porous media. Time-resolved particle image velocimetry (PIV) is used to visualize the velocity field in a low aspect ratio bed with 15 mm glass beads. An aqueous solution of Ammunium Thiocynante is used as the working fluid to facilitate matching the solid-fluid refractiveindices. In order to illuminate the inertial regime characteristics, two pore Reynolds number of 100 and 270 are examined. Also, due to the random nature of the packing several pore geometries are compared to identify local scaling used to define the inertial regime effects. Discrete vortical flow structures are evaluated using LES (lowpass filtering) decomposition, in conjunction with criticalpoint analysis of the local velocity gradient tensor. The identified scales associated with the vortical elements are compared based on Reynolds number and pore geometry. Implementing circulation as an integral measure of all vortical structures locally at the pore-scale level demonstrated a linear attitude over the range of Reynolds numbers. Evolution of inertial effects within pore-regions are indicated to be the primary driving mechanism for the emergence of swirling structures passing through the PIV field of view at the onset of turbulence. KEYWORDS Particle image velocimetry (PIV), vortex identification, vorti-cal structure, transition to turbulence, porous media, inertial flow regime, random packed bed, refractive index matched (RIM/MIR) NOMENCLATURE d p [µm] Diameter of PIV tracer particles β [mm] Characteristic length scale of fluid phase n L Liquid refractive index n S Solid refractive index D B [m] Bead diameter D H [m] Hydraulic diameter D tracer [m] Tracer particle diameter L x [mm] Test section width x-direction L y [mm] Test section height y-direction Re p Pore Reynolds number Re P local Local Pore Reynolds number V Darcy [mm/s] Superficial or Darcy velocity V int [m/s] Interstitial velocity Γ 1 [m 2 /s] Vortex center identification scheme Γ [m 2 /s] Circulation λ [nm] Wavelength of light λ ci [1/s] Swirl strength µ [Kg/ms] Dynamic viscosity of fluid phase ν [m 2 /s] Kinematic viscosity of fluid phase φ Porosity ρ [Kg/m 3 ] Density of fluid phase ρ p [gr/cm 3 ] Density of PIV tracer particles rms Root mean square St p The stokes number of PIV tracer particles 1