scholarly journals Time-resolved sphere and fluid motions in turbulent boundary layers

2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Yi Hui Tee ◽  
Ellen K. Longmire
Keyword(s):  
Coherent Structures ◽  
Fluid Motion ◽  
Terminal Velocity ◽  
Stereoscopic Particle Image Velocimetry ◽  
Wall Friction ◽  
Time Resolved ◽  
Image Velocimetry ◽  
Slow Moving ◽  
Lift Off ◽  
Streamwise Distance

This paper extends the study by Tee et al. (2020) to investigate the effect of large coherent structures on motion of spheres with specific gravities of 1.006 (P1) and 1.152 (P3) at Reτ = 670 and 1300 (d+ = 56 and 116). The sphere and fluid motions are tracked simultaneously via 3D particle tracking and stereoscopic particle image velocimetry over the streamwise-spanwise plane, respectively. With sufficient mean shear, sphere P1 lifts off of the wall upon release before descending back towards the wall at both Reτ. It typically accelerates strongly over a streamwise distance of less than one boundary layer thickness before approaching an approximate terminal velocity. By contrast, the denser sphere P3 does not lift off upon release but mainly slides along the wall. At lower Reτ where wall friction is stronger, this sphere translates with unsteady velocity, significantly lagging the local fluid. The streamwise velocities of both spheres correlate strongly with the fast- and slow-moving zones that approach and move over them. In most runs, both spheres lag the local coherent structures and travel with either fast- or slow-moving zones throughout the observed trajectories. Vortex shedding, which is most prevalent for sphere P3 at Reτ = 670, is also important. The sphere spanwise motion is prompted by wall friction, spanwise fluid motion, and/or meandering of the coherent structures, and spheres do not appear to migrate preferentially into slow-moving zones.

Stereoscopic Particle Image Velocimetry Analysis of Healthy and Emphysemic Alveolar Sac Models

2011 ◽  
Vol 133 (6) ◽  
Author(s):  
Emily J. Berg ◽  
Risa J. Robinson
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Fluid Motion ◽  
Three Dimensional ◽  
Flow Fields ◽  
Stereoscopic Particle Image Velocimetry ◽  
Recirculating Flow ◽  
Image Velocimetry ◽  
Flow Speeds ◽  
Healthy Lung

Emphysema is a progressive lung disease that involves permanent destruction of the alveolar walls. Fluid mechanics in the pulmonary region and how they are altered with the presence of emphysema are not well understood. Much of our understanding of the flow fields occurring in the healthy pulmonary region is based on idealized geometries, and little attention has been paid to emphysemic geometries. The goal of this research was to utilize actual replica lung geometries to gain a better understanding of the mechanisms that govern fluid motion and particle transport in the most distal regions of the lung and to compare the differences that exist between healthy and emphysematous lungs. Excised human healthy and emphysemic lungs were cast, scanned, graphically reconstructed, and used to fabricate clear, hollow, compliant models. Three dimensional flow fields were obtained experimentally using stereoscopic particle image velocimetry techniques for healthy and emphysematic breathing conditions. Measured alveolar velocities ranged over two orders of magnitude from the duct entrance to the wall in both models. Recirculating flow was not found in either the healthy or the emphysematic model, while the average flow rate was three times larger in emphysema as compared to healthy. Diffusion dominated particle flow, which is characteristic in the pulmonary region of the healthy lung, was not seen for emphysema, except for very small particle sizes. Flow speeds dissipated quickly in the healthy lung (60% reduction in 0.25 mm) but not in the emphysematic lung (only 8% reduction 0.25 mm). Alveolar ventilation per unit volume was 30% smaller in emphysema compared to healthy. Destruction of the alveolar walls in emphysema leads to significant differences in flow fields between the healthy and emphysemic lung. Models based on replica geometry provide a useful means to quantify these differences and could ultimately improve our understanding of disease progression.

scholarly journals Investigation of Film Cooling Using Time-Resolved Stereo Particle Image Velocimetry

2021 ◽  
Vol 143 (7) ◽  
Author(s):  
Katharina Stichling ◽  
Maximilian Elfner ◽  
Hans-Jörg Bauer
Keyword(s):  
Particle Image Velocimetry ◽  
Film Cooling ◽  
Particle Image ◽  
Operating Conditions ◽  
Stereoscopic Particle Image Velocimetry ◽  
Test Rig ◽  
Time Resolved ◽  
Hot Gas ◽  
Image Velocimetry ◽  
Cooling Air

Abstract In the present study, an existing test rig at the Institute of Thermal Turbomachinery (ITS), Karlsruhe Institute of Technology (KIT), designed for generic film cooling studies is adopted to accommodate time-resolved stereoscopic particle image velocimetry (SPIV) measurements. Through a similarity analysis, the test rig geometry is scaled by a factor of about 20. Operating conditions of hot gas and cooling air inlet and exit can be imposed that are compliant with realistic engine conditions including density ratio (DR). The cooling air is supplied by a parallel-to-hot gas coolant flow-configuration with a coolant Reynolds number of 30, 000. Time-resolved and time-averaged stereo article image velocimetry data for a film cooling flow at high DR and a range of blowing ratios are presented in this study. The investigated film cooling hole constitutes a 10 deg–10 deg–10 deg laidback fan-shaped hole with a wide spacing of P/D = 8 to insure the absence of jet interaction. The inclination angle amounts to 35 deg. The time-resolved data indicate transient behavior of the film cooling jet.

Jet-noise control by fluidic injection from a rotating plug: linear and nonlinear sound-source mechanisms

2016 ◽  
Vol 788 ◽  
pp. 358-380 ◽  
Author(s):  
Maxime Kœnig ◽  
Kenzo Sasaki ◽  
André V. G. Cavalieri ◽  
Peter Jordan ◽  
Yves Gervais
Keyword(s):  
Coherent Structures ◽  
Stereoscopic Particle Image Velocimetry ◽  
Linear Stability Theory ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Wave Interactions ◽  
Time Resolved ◽  
Source Mechanisms ◽  
The Mean ◽  
Flow Deformation

We present a study of the turbulent and acoustic fields of subsonic jets, controlled by means of a novel actuator that introduces perturbations via steady-fluidic actuation from a rotating centrebody. The actuation can produce louder or quieter jets, and these are analysed using time-resolved stereoscopic particle image velocimetry and a hot-wire anemometer. We place the analysis in the framework of wavepackets and linear stability theory, whence we show, using solutions of the linear parabolised stability equations, that the quieter flows can be understood to result from a mean-flow deformation that modifies wavepacket dynamics, and in particular their phase velocities, which are significantly reduced. The mean-flow deformation is shown, by a triple decomposition, to be due to the generation of Reynolds stresses associated with incoherent turbulence (rather than coherent structures) which arises when the actuation energises the flow with a frequency–azimuthal wavenumber (${\it\omega}$–$m$) combination to which the mean flow is stable. When the actuation excites the flow with an ${\it\omega}$–$m$ combination to which the mean flow is unstable, the response is dominated by coherent structures, whose rapid growth takes them beyond the linear limit, where they undergo quadratic wave interactions and lead, consequently, to a louder flow.

scholarly journals Effect of Gust Wind on Flow over a Wall-Mounted Fence

2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Dhanush Bhamitipadi Suresh ◽  
Emmanuvel Joseph Aju ◽  
Matthew John Zaksek ◽  
Melissa Marie Leffingwell ◽  
Yaqing Jin
Keyword(s):  
Particle Image ◽  
Wind Gust ◽  
Wind Tunnel Experiments ◽  
Time Resolved ◽  
Wake Flows ◽  
Flow Mixing ◽  
Image Velocimetry ◽  
Before And After ◽  
Wind Flows ◽  
Streamwise Distance

In this work, the characteristics of incoming and wake flows downstream of wall-mounted fences under wind gust were explored with wind tunnel experiments. A time-resolved particle image velocimetry was used to capture the flow dynamics across two different fence heights. The results show that during the gust period, the wake presents distinct meandering and strong flow mixing. The Probability Density Function distribution of flow velocities indicates that the mixing effect increases with the streamwise distances. Specifically, for locations above the fence top tip, the growth of streamwise distance decreases the footprint of wind gust. However, for locations lower than the fence top tip, the local wind flows exhibit stronger variations before and after wind gust with the growth of downstream distance. Overall, at the same relative streamwise and spanwise locations downstream of fences within the wake region, the higher fence better suppresses the influence of gust wind.

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