scholarly journals Investigation of large scale motions in zero and adverse pressure gradient turbulent boundary layers using high-spatial-resolution particle image velocimetry

2021 ◽  
pp. 110469
Author(s):  
Muhammad Shehzad ◽  
Bihai Sun ◽  
Daniel Jovic ◽  
Yasar Ostovan ◽  
Christophe Cuvier ◽  
...  
Keyword(s):  
Particle Image Velocimetry ◽  
Pressure Gradient ◽  
Boundary Layers ◽  
Spatial Resolution ◽  
Large Scale ◽  
Particle Image ◽  
High Spatial Resolution ◽  
Adverse Pressure Gradient ◽  
Turbulent Boundary Layers ◽  
Image Velocimetry

scholarly journals Investigation of Large Scale Motions in Zero and Adverse Pressure Gradient Turbulent Boundary Layers Using High-Spatial-Resolution PIV

2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Daniel Jovic ◽  
Muhammad Shehzad ◽  
Bihai Sun ◽  
Christophe Cuvier ◽  
Christian Willert ◽  
...  
Keyword(s):  
Pressure Gradient ◽  
Spatial Resolution ◽  
Large Scale ◽  
High Spatial Resolution ◽  
Adverse Pressure Gradient ◽  
Velocity Fields ◽  
Small Scale ◽  
Measured Velocity ◽  
Image Velocimetry ◽  
High Reynolds

Particle image velocimetry (PIV) has been used to capture the high-spatial-resolution (HSR) two-component, two-dimensional (2C-2D) velocity fields of a zero-pressure-gradient (ZPG) turbulent boundary layer (TBL) and of an adverse-pressure-gradient (APG) TBL. Proper Orthogonal Decomposition (POD) is performed on the measured velocity fields to characterize the velocity fields as large or small scale motions (LSMs or SSMs), with further characterisation of the LSMs into high and low momentum events. This paper reports the findings of the PIV experiment and the subsequent analysis of the high Reynolds number ZPG and APG TBLs

Pressure gradient effects on the large-scale structure of turbulent boundary layers

2013 ◽  
Vol 715 ◽  
pp. 477-498 ◽  
Author(s):  
Zambri Harun ◽  
Jason P. Monty ◽  
Romain Mathis ◽  
Ivan Marusic
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Pressure Gradient ◽  
Boundary Layers ◽  
Amplitude Modulation ◽  
Large Scale ◽  
Outer Region ◽  
Adverse Pressure Gradient ◽  
Turbulent Boundary Layers ◽  
Small Scale

AbstractResearch into high-Reynolds-number turbulent boundary layers in recent years has brought about a renewed interest in the larger-scale structures. It is now known that these structures emerge more prominently in the outer region not only due to increased Reynolds number (Metzger & Klewicki, Phys. Fluids, vol. 13(3), 2001, pp. 692–701; Hutchins & Marusic, J. Fluid Mech., vol. 579, 2007, pp. 1–28), but also when a boundary layer is exposed to an adverse pressure gradient (Bradshaw, J. Fluid Mech., vol. 29, 1967, pp. 625–645; Lee & Sung, J. Fluid Mech., vol. 639, 2009, pp. 101–131). The latter case has not received as much attention in the literature. As such, this work investigates the modification of the large-scale features of boundary layers subjected to zero, adverse and favourable pressure gradients. It is first shown that the mean velocities, turbulence intensities and turbulence production are significantly different in the outer region across the three cases. Spectral and scale decomposition analyses confirm that the large scales are more energized throughout the entire adverse pressure gradient boundary layer, especially in the outer region. Although more energetic, there is a similar spectral distribution of energy in the wake region, implying the geometrical structure of the outer layer remains universal in all cases. Comparisons are also made of the amplitude modulation of small scales by the large-scale motions for the three pressure gradient cases. The wall-normal location of the zero-crossing of small-scale amplitude modulation is found to increase with increasing pressure gradient, yet this location continues to coincide with the large-scale energetic peak wall-normal location (as has been observed in zero pressure gradient boundary layers). The amplitude modulation effect is found to increase as pressure gradient is increased from favourable to adverse.

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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