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.

Experimental study of the mean structure and quasi-conical scaling of a swept-compression-ramp interaction at Mach 2

2018 ◽  
Vol 841 ◽  
pp. 1-27 ◽  
Author(s):  
Leon Vanstone ◽  
Mustafa Nail Musta ◽  
Serdar Seckin ◽  
Noel Clemens
Keyword(s):  
Boundary Layer ◽  
Shock Wave ◽  
Particle Image Velocimetry ◽  
Flow Field ◽  
Scaling Laws ◽  
Particle Image ◽  
Separated Flow ◽  
Image Velocimetry ◽  
The Mean ◽  
Wave Boundary

This study investigates the mean flow structure of two shock-wave boundary-layer interactions generated by moderately swept compression ramps in a Mach 2 flow. The ramps have a compression angle of either $19^{\circ }$ or $22.5^{\circ }$ and a sweep angle of $30^{\circ }$. The primary diagnostic methods used for this study are surface-streakline flow visualization and particle image velocimetry. The shock-wave boundary-layer interactions are shown to be quasi-conical, with the intermittent region, separation line and reattachment line all scaling in a self-similar manner outside of the inception region. This is one of the first studies to investigate the flow field of a swept ramp using particle image velocimetry, allowing more sensitive measurements of the velocity flow field than previously possible. It is observed that the streamwise velocity component outside of the separated flow reaches the quasi-conical state at the same time as the bulk surface flow features. However, the streamwise and cross-stream components within the separated flow take longer to recover to the quasi-conical state, which indicates that the inception region for these low-magnitude velocity components is actually larger than was previously assumed. Specific scaling laws reported previously in the literature are also investigated and the results of this study are shown to scale similarly to these related interactions. Certain limiting cases of the scaling laws are explored that have potential implications for the interpretation of cylindrical and quasi-conical scaling.

Investigation of Unsteady Wake-Separated Boundary Layer Interaction Using Particle-Image-Velocimetry

2007 ◽  
Author(s):  
Og˘uz Uzol ◽  
Xue Feng Zhang ◽  
Alex Cranstone ◽  
Howard Hodson
Keyword(s):  
Boundary Layer ◽  
Particle Image Velocimetry ◽  
Shear Layer ◽  
Particle Image ◽  
Separation Bubble ◽  
Free Shear Layer ◽  
Unsteady Boundary Layer ◽  
Layer Interaction ◽  
Image Velocimetry ◽  
Boundary Layer Interaction

The current paper presents an experimental investigation of the interaction between unsteady wakes and the separated boundary layer on the suction side of an ultra-high-lift low-pressure turbine airfoil. Two-dimensional Particle Image Velocimetry (PIV) measurements of the unsteady boundary layer over the T106C LP turbine profile were performed in a low speed linear cascade facility, at selected phases of passing wakes. The wakes are created by moving cylindrical bars across the inlet of the test section. Various phenomena were investigated such as separation and transition characteristics, vortex structures within the unsteady boundary layer, their interaction and effects on the transition process, the corresponding vortex shedding mechanisms and the unsteady behaviour of the separation bubble due to the wake- boundary layer interaction. The current measurements suggest that rollup vortices are generated as the wake approaches the separated shear layer on the suction surface before the wake centerline starts impinging on the blade. At this instant, the bubble is sufficiently high for the free shear layer to roll up into a vortex and the incoming wake is highly distorted (strained) due to the velocity field within the blade passage, and the turbulence distribution within the wake is not symmetrical. Vortices within the boundary layer, identified using the swirl strength distributions calculated from the eigenvalues of the velocity gradient tensor, seem to be coalescing and forming bigger scale structures, which in turn break up into smaller but higher swirl strength eddies. In between the passing wakes, the separation bubble grows in both in height and length, trying to return to its steady state shape.

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.

Particle-Image Velocimetry Measurements of Film Cooling in an Adverse Pressure Gradient Flow

2010 ◽  
Author(s):  
Wilhelm Jessen ◽  
Martin Konopka ◽  
Wolfgang Schro¨der
Keyword(s):  
Boundary Layer ◽  
Particle Image Velocimetry ◽  
Pressure Gradient ◽  
Film Cooling ◽  
Boundary Layer Thickness ◽  
Particle Image ◽  
Density Ratio ◽  
Adverse Pressure Gradient ◽  
Velocity Fluctuations ◽  
Image Velocimetry

The turbulent flow field of a film cooling flow is investigated using the particle-image velocimetry (PIV) technique. Cooling jets are injected from a multi-row hole configuration into a turbulent boundary layer flow of a flat plate in the presence of a zero and an adverse pressure gradient. The investigations focus on full-coverage film cooling. Therefore, the film cooling configuration consists of three staggered rows of holes with a lateral spacing of p/D = 3 and a streamwise row distance of l/D = 6. The inclined cooling holes feature a fan-shaped exit geometry with lateral and streamwise expansions. Jets of air and CO2 are injected separately at different blowing ratios into a boundary layer to examine the effects of the density ratio between coolant and mainstream on the mixing behavior and consequently, the cooling efficiency. For the zero pressure gradient case the measurement results indicate the different nature of the mixing process between the jets and the crossflow after the first, second, and third row. The mainstream velocity distributions evidence the growth of the boundary layer thickness at increasing row number. The interaction between the undisturbed boundary layer and first two rows leads to maximum values of turbulent kinetic energy. The presence of an adverse pressure gradient in the mainstream clearly intensifies the growth of the boundary layer thickness and increases the velocity fluctuations in the upper mixing zone. The measurements considering an increased density ratio show higher turbulence intensities in the shear zone between the jets and the main flow leading to a more pronounced mixing in this area. The results of the experimental measurements are used to validate numerical findings from a large-eddy simulation. This comparison shows a very good agreement for mean velocity distributions and velocity fluctuations.

scholarly journals Investigation of Reverse Swing and Magnus Effect on a Cricket Ball Using Particle Image Velocimetry

2020 ◽  
Vol 10 (22) ◽  
pp. 7990
Author(s):  
Richard W. Jackson ◽  
Edmund Harberd ◽  
Gary D. Lock ◽  
James A. Scobie
Keyword(s):  
Boundary Layer ◽  
Particle Image Velocimetry ◽  
Flow Separation ◽  
Particle Image ◽  
Separation Bubble ◽  
Laminar Separation ◽  
Magnus Effect ◽  
Cricket Ball ◽  
Image Velocimetry ◽  
First Time

Lateral movement from the principal trajectory, or “swing”, can be generated on a cricket ball when its seam, which sits proud of the surface, is angled to the flow. The boundary layer on the two hemispheres divided by the seam is governed by the Reynolds number and the surface roughness; the swing is fundamentally caused by the pressure differences associated with asymmetric flow separation. Skillful bowlers impart a small backspin to create gyroscopic inertia and stabilize the seam position in flight. Under certain flow conditions, the resultant pressure asymmetry can reverse across the hemispheres and “reverse swing” will occur. In this paper, particle image velocimetry measurements of a scaled cricket ball are presented to interrogate the flow field and the physical mechanism for reverse swing. The results show that a laminar separation bubble forms on the non-seam side (hemisphere), causing the separation angle for the boundary layer to be increased relative to that on the seam side. For the first time, it is shown that the separation bubble is present even under large rates of backspin, suggesting that this flow feature is present under match conditions. The Magnus effect on a rotating ball is also demonstrated, with the position of flow separation on the upper (retreating) side delayed due to the reduced relative speed between the surface and the freestream.

Particle-Image Velocimetry Measurements of Film Cooling in an Adverse Pressure Gradient Flow

2011 ◽  
Vol 134 (2) ◽  
Author(s):  
Wilhelm Jessen ◽  
Martin Konopka ◽  
Wolfgang Schroeder
Keyword(s):  
Boundary Layer ◽  
Particle Image Velocimetry ◽  
Pressure Gradient ◽  
Film Cooling ◽  
Boundary Layer Thickness ◽  
Particle Image ◽  
Density Ratio ◽  
Adverse Pressure Gradient ◽  
Velocity Fluctuations ◽  
Image Velocimetry

The turbulent flow field of a film cooling flow is investigated using the particle-image velocimetry technique. Cooling jets are injected from a multirow hole configuration into a turbulent boundary layer flow of a flat plate in the presence of a zero and an adverse pressure gradient. The investigations focus on full-coverage film cooling. Therefore, the film cooling configuration consists of three staggered rows of holes with a lateral spacing of p/D=3 and a streamwise row distance of l/D=6. The inclined cooling holes feature a fan-shaped exit geometry with lateral and streamwise expansions. Jets of air and CO2 are injected separately at different blowing ratios into a boundary layer to examine the effects of the density ratio between coolant and mainstream on the mixing behavior and consequently, the cooling efficiency. For the zero pressure gradient case, the measurement results indicate the different nature of the mixing process between the jets and the crossflow after the first, second, and third row. The mainstream velocity distributions evidence the growth of the boundary layer thickness at increasing row number. The interaction between the undisturbed boundary layer and first two rows leads to maximum values of turbulent kinetic energy. The presence of an adverse pressure gradient in the mainstream clearly intensifies the growth of the boundary layer thickness and increases the velocity fluctuations in the upper mixing zone. The measurements considering an increased density ratio show higher turbulence intensities in the shear zone between the jets and the main flow, leading to a more pronounced mixing in this area. The results of the experimental measurements are used to validate numerical findings from a large-eddy simulation. This comparison shows a very good agreement for mean velocity distributions and velocity fluctuations.

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