scholarly journals Particle image velocimetry measurements of the interaction of synthetic jets with a zero-pressure gradient laminar boundary layer

2010 ◽  
Vol 22 (6) ◽  
pp. 063603 ◽  
Author(s):  
Mark Jabbal ◽  
Shan Zhong
Keyword(s):  
Boundary Layer ◽  
Particle Image Velocimetry ◽  
Pressure Gradient ◽  
Laminar Boundary Layer ◽  
Particle Image ◽  
Synthetic Jets ◽  
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.

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.

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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