Time-resolved particle image velocimetry measurements of vortex and shear layer dynamics in the near wake of a tethered sphere

2013 ◽  
Vol 25 (7) ◽  
pp. 077102 ◽  
Author(s):  
R. van Hout ◽  
A. Katz ◽  
D. Greenblatt
Keyword(s):  
Particle Image Velocimetry ◽  
Shear Layer ◽  
Particle Image ◽  
Near Wake ◽  
Time Resolved ◽  
Image Velocimetry

scholarly journals Time-resolved particle image velocimetry measurements of the turbulent Richtmyer–Meshkov instability

2021 ◽  
Vol 917 ◽  
Author(s):  
Everest G. Sewell ◽  
Kevin J. Ferguson ◽  
Vitaliy V. Krivets ◽  
Jeffrey W. Jacobs
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Time Resolved ◽  
Image Velocimetry

Abstract

Time-Resolved Particle Image Velocimetry (PIV) Measurements in a Radial Diffuser Pump

2009 ◽  
Author(s):  
Jianjun Feng ◽  
Friedrich-Karl Benra ◽  
Hans Josef Dohmen
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Time Resolved ◽  
Piv Measurements ◽  
Part Load ◽  
Channel Characteristic ◽  
Image Velocimetry ◽  
Pump Stage ◽  
Low Specific Speed ◽  
Load Conditions

The truly time-variant unsteady flow in a low specific speed radial diffuser pump stage has been investigated by time-resolved Particle Image Velocimetry (PIV) measurements. The measurements are conducted at the midspan of the blades for the design condition and also for some severe part-load conditions. The instantaneous flow fields among different impeller channels are analyzed and compared in detail, and more attention has been paid to flow separations at part-load conditions. The analysis of the measured results shows that the flow separations at two adjacent impeller channels are quite different at some part-load conditions. The separations generally exhibit a two-channel characteristic.

Entrainment and topology of accelerating shear layers

2016 ◽  
Vol 811 ◽  
pp. 37-50 ◽  
Author(s):  
Giuseppe A. Rosi ◽  
David E. Rival
Keyword(s):  
Shear Layer ◽  
Particle Image ◽  
Point Vortex ◽  
Reynolds Numbers ◽  
Shear Layers ◽  
Circular Path ◽  
Entrainment Rate ◽  
Time Resolved ◽  
And Topology ◽  
Image Velocimetry

A constantly accelerating circular plate was investigated towards understanding the effect of non-stationarity on shear-layer entrainment and topology. Dye visualizations and time-resolved particle image velocimetry measurements were collected for normalized accelerations spanning three orders of magnitude. Increasing acceleration acts to organize shear-layer topology. Specifically, the Kelvin–Helmholtz instabilities within the shear layer better adhered to a circular path and exhibited consistent and repeatable spacing. Normalized starting-vortex circulation was observed to collapse with increasing acceleration, which one might not expect due to increased levels of mixing at higher instantaneous Reynolds numbers. The entrainment rate was shown to increase nonlinearly with increasing acceleration. This was attributed to closer spacing between instabilities, which better facilitates the roll-up of fluid between the shear layer and vortex core. The shear-layer organization observed at higher accelerations was associated with smaller spacings between instabilities. Specifically, analogous point-vortex simulations demonstrated that decreasing the spacing between instabilities acts to localize and dampen perturbations within an accelerating shear layer.

scholarly journals Particle image velocimetry measurements of induced separation at the leading edge of a plate

2016 ◽  
Vol 804 ◽  
pp. 278-297 ◽  
Author(s):  
J. P. J. Stevenson ◽  
K. P. Nolan ◽  
E. J. Walsh
Keyword(s):  
Particle Image Velocimetry ◽  
Shear Layer ◽  
Particle Image ◽  
Reverse Flow ◽  
Leading Edge ◽  
Quadrant Analysis ◽  
Bypass Transition ◽  
Reynolds Stresses ◽  
Free Stream Turbulence ◽  
Image Velocimetry

The free shear layer that separates from the leading edge of a round-nosed plate has been studied under conditions of low (background) and elevated (grid-generated) free stream turbulence (FST) using high-fidelity particle image velocimetry. Transition occurs after separation in each case, followed by reattachment to the flat surface of the plate downstream. A bubble of reverse flow is thereby formed. First, we find that, under elevated (7 %) FST, the time-mean bubble is almost threefold shorter due to an accelerated transition of the shear layer. Quadrant analysis of the Reynolds stresses reveals the presence of slender, highly coherent fluctuations amid the laminar part of the shear layer that are reminiscent of the boundary-layer streaks seen in bypass transition. Instability and the roll-up of vortices then follow near the crest of the shear layer. These vortices are also present under low FST and in both cases are found to make significant contributions to the production of Reynolds stress over the rear of the bubble. But their role in reattachment, whilst important, is not yet fully clear. Instantaneous flow fields from the low-FST case reveal that the bubble of reverse flow often breaks up into two or more parts, thereby complicating the overall reattachment process. We therefore suggest that the downstream end of the ‘separation isoline’ (the locus of zero absolute streamwise velocity that extends unbroken from the leading edge) be used to define the instantaneous reattachment point. A histogram of this point is found to be bimodal: the upstream peak coincides with the location of roll-up, whereas the downstream mode may suggest a ‘flapping’ motion.

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