Particle-image velocimetry and force measurements of leading-edge serrations on owl-based wing models

2014 ◽  
Vol 11 (3) ◽  
pp. 423-438 ◽  
Author(s):  
Andrea Winzen ◽  
Benedikt Roidl ◽  
Stephan Klän ◽  
Michael Klaas ◽  
Wolfgang Schröder
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Leading Edge ◽  
Force Measurements ◽  
Image Velocimetry

Characteristics of a separated flow past a semicircular leading-edge airfoil model under different imposed pressure gradient

2021 ◽  
pp. 095441002110212
Author(s):  
K Anand ◽  
KT Ganesh
Keyword(s):  
Boundary Layer ◽  
Particle Image Velocimetry ◽  
Pressure Gradient ◽  
Particle Image ◽  
Separation Bubble ◽  
Separated Flow ◽  
Leading Edge ◽  
Field Measurements ◽  
Bench Mark ◽  
Image Velocimetry

The effect of pressure gradient on a separated boundary layer past the leading edge of an airfoil model is studied experimentally using electronically scanned pressure (ESP) and particle image velocimetry (PIV) for a Reynolds number ( Re) of 25,000, based on leading-edge diameter ( D). The features of the boundary layer in the region of separation and its development past the reattachment location are examined for three cases of β (−30°, 0°, and +30°). The bubble parameters such as the onset of separation and transition and the reattachment location are identified from the averaged data obtained from pressure and velocity measurements. Surface pressure measurements obtained from ESP show a surge in wall static pressure for β = −30° (flap deflected up), while it goes down for β = +30° (flap deflected down) compared to the fundamental case, β = 0°. Particle image velocimetry results show that the roll up of the shear layer past the onset of separation is early for β = +30°, owing to higher amplification of background disturbances compared to β = 0° and −30°. Downstream to transition location, the instantaneous field measurements reveal a stretched, disoriented, and at instances bigger vortices for β = +30°, whereas a regular, periodically shed vortices, keeping their identity past the reattachment location, is observed for β = 0° and −30°. Above all, this study presents a new insight on the features of a separation bubble receiving a disturbance from the downstream end of the model, and these results may serve as a bench mark for future studies over an airfoil under similar environment.

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.

scholarly journals Experimental measurements of the flow field around a film-cooled blade leading edge using particle image velocimetry

2018 ◽  
Vol 10 (10) ◽  
pp. 168781401880290
Author(s):  
José Omar Dávalos Ramírez ◽  
Juan Carlos García Castrejón ◽  
Francisco Carrillo Pereyra ◽  
Carlos Ponce Corral ◽  
Carlos Felipe Ramírez Espinoza ◽  
...  
Keyword(s):  
Particle Image Velocimetry ◽  
Flow Field ◽  
Particle Image ◽  
Leading Edge ◽  
Cooling Flow ◽  
Image Velocimetry ◽  
Secondary Vortices ◽  
Velocity Turbulence ◽  
Cooled Blade ◽  
Blade Leading Edge

In this article, particle image velocimetry studies were conducted in a low-speed wind tunnel to investigate the effects of blowing ratio and blade span in terms of the characteristics of the flow field around a film-cooled blade leading edge. The measurements were performed at 20%, 40%, 60%, and 80% of blade span and blowing ratios of M = 0.5, M = 0.75, M = 1, M = 1.5, and M = 2. Velocity, turbulence intensity, and structure of vortices during the interaction between cooling flow and mainstream were analyzed in detail. The analysis shows a significant increase in mainstream velocity at low blowing ratios, M < 1. Peaks of turbulence were observed at low- and high-span locations. Aerodynamical losses are expected at higher blowing ratios due to the formation of secondary vortices near the outgoing jet. These vortices were a consequence of velocity gradients at this zone.

Stereo three-dimensional particle image velocimetry measurement and aerodynamic force analysis of non-spinning soccer balls

2020 ◽  
Vol 234 (2) ◽  
pp. 146-153 ◽  
Author(s):  
Masaki Hiratsuka ◽  
Shinichiro Ito ◽  
Keita Miyasaka ◽  
Akihisa Konno
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Aerodynamic Force ◽  
Three Dimensional ◽  
Jet Flow ◽  
Flight Path ◽  
Wake Flow ◽  
Force Measurements ◽  
Flow Measurements ◽  
Image Velocimetry

A knuckle shot, resulting from non-spinning kicking, is an essential technique in soccer. The irregular flight path of the knuckle shot is caused by the aerodynamic force from the three-dimensional twin vortices generated in the wake behind the ball. However, the detailed behavior of the twin vortices and relation between the jet flow and the acting forces on the balls is still not understood. In addition, a more thorough understanding of the effect of ball panels on the formation of twin vortices and jet flow is important to develop balls with high controllability. To study the effect of the ball panel shape on the flight path, stereo three-dimensional particle image velocimetry wake flow measurements and synchronized force measurements were performed on various soccer balls. It was confirmed that the aerodynamic force on the ball is produced by the jet flow generated by the vortices in the wake flow. The directions of the force followed the changes of the jet flow, and the magnitude of the force was strongly associated with the flow rate of the jet. Moreover, the shape of the ball panels, especially the groove volume, determines the critical Reynolds number and the fluttering of the balls.

Discrepancy in the Aerodynamic Property and Flowfield of a Symmetric Airfoil Produced by the Stationary and Moving Ground Effect

2020 ◽  
Vol 143 (2) ◽  
Author(s):  
V. Tremblay-Dionne ◽  
T. Lee
Keyword(s):  
Boundary Layer ◽  
Particle Image Velocimetry ◽  
Particle Image ◽  
Ground Surface ◽  
Leading Edge ◽  
Ground Effect ◽  
Edge Region ◽  
Flow Passage ◽  
Image Velocimetry ◽  
Aerodynamic Property

Abstract The discrepancy in the aerodynamic property and flowfield of a symmetric airfoil produced by the stationary and moving ground effect was quantified through surface pressure and particle-image-velocimetry measurements. The results show that the stationary ground effect produced a higher lift than the moving ground due to the flow passage restriction caused by the longitudinal boundary layer developed on its ground surface. In close ground proximity, the formation of a ground vortex beneath the airfoil's leading-edge region speeded up the flow, leading to a lower lift than its moving-ground counterpart. For the moving ground, the ground vortex was absent. In close ground proximity, the moving ground effect generated a larger wake and drag than the stationary ground effect.

Wind tunnel study of separated and reattaching flows by particle image velocimetry and pressure measurements

2019 ◽  
Vol 22 (7) ◽  
pp. 1769-1782 ◽  
Author(s):  
ZR Shu ◽  
QS Li
Keyword(s):  
Reynolds Number ◽  
Particle Image Velocimetry ◽  
Turbulence Intensity ◽  
Particle Image ◽  
Leading Edge ◽  
Length Scale ◽  
Pressure Measurements ◽  
Pressure Coefficients ◽  
Image Velocimetry ◽  
The Mean

This article presents a comprehensive investigation on the separated and reattaching flows over a blunt flat plate with different leading-edge shapes by means of particle image velocimetry and surface pressure measurements. Wind tunnel tests are performed in both smooth and various turbulent flow conditions, and the separated and reattaching flows are examined as a function of Reynolds number ( Re), leading-edge shape, turbulence intensity, and turbulence integral length scale. It is shown through the particle image velocimetry and pressure measurements that the Reynolds number effect is significant regarding the mean vorticity field, but with little effect on the mean velocity field. For the effects of leading-edge shape, the distributions of pressure coefficients respond strongly to the change in leading-edge angle, and both the velocity (streamwise and vertical) and vorticity fields have a clear dependence on the leading-edge shape. For the effects of freestream turbulence, the mean pressure coefficient responds strongly to turbulence intensity, whereas the fluctuating and peak suction pressure coefficients are dependent on both turbulence intensity and integral length scale. The size of the separation bubble contracts aggressively with increasing turbulence intensity, but it remains approximately invariant in response to the change in turbulence scale in the tested range.

The Study of Blockages Effect at Leading Edge on Rectangular Cavity in Subsonic Flow Using Particle Image Velocimetry (PIV)

2013 ◽  
Vol 300-301 ◽  
pp. 781-784
Author(s):  
Ahsan Nur Mubarak Annuar ◽  
Azmin Shakrine M. Rafie ◽  
Mohamed Thariq Hameed Sultan
Keyword(s):  
Particle Image Velocimetry ◽  
Velocity Profile ◽  
Particle Image ◽  
Cavity Length ◽  
Leading Edge ◽  
Rectangular Cavity ◽  
Mean Velocity ◽  
Subsonic Wind Tunnel ◽  
Image Velocimetry ◽  
Image Pairs

In this present paper, laminar cavity flow is analysed at Re = 5.12 x 104 based on cavity length. The experiments were conducted in an open subsonic wind tunnel using Particle Image Velocimetry (PIV). A rectangular cavity with constant depth of 4 cm with length-to-depth ratio of 4 was used. Several types of blockage had been located at the leading edge of cavity and each experiment was performed by acquiring 700 image pairs to filter out the velocity vectors. The results are given in terms of mean velocity profile accordingly and compared thoroughly by dividing cavity into 4 sections. The result had been shown in mean velocity profile in u and v velocity component.

Sign in / Sign up

Export Citation Format

Share Document