Similarity Scaling for the Inner Region of the Turbulent Boundary Layer

2009 ◽  
Author(s):  
David W. Weyburne
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Similarity Scaling ◽  
Inner Region

Modification of Near-Wall Structure in a Shear-Driven 3-D Turbulent Boundary Layer

2001 ◽  
Vol 124 (1) ◽  
pp. 118-126 ◽  
Author(s):  
Robert O. Kiesow ◽  
Michael W. Plesniak
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Reynolds Shear Stress ◽  
Power Spectra ◽  
Streamwise Velocity ◽  
Wall Structure ◽  
Reynolds Stresses ◽  
Planar Shear ◽  
Inner Region ◽  
Near Wall

The near-wall physics of a planar, shear-driven, 3-D turbulent boundary layer with varying strengths of crossflow are examined. Flow visualization data reveals a reduction of mean streak length by as much as 50% with increasing spanwise shear. Power spectra of velocity confirm this shift towards higher temporal frequencies, corresponding to decreased streamwise length scales. PIV measurements indicate a significant modification of the inner region of the boundary layer with increasing spanwise shear. Streamwise velocity profiles exhibit an increasing velocity deficit with increased crossflow. Increased levels of the normal Reynolds stresses u′2¯ and v′2¯ and an increase in the −u′v′¯ Reynolds shear stress are also observed. Modifications in the spanwise and transverse vorticity were also observed at higher shear rates.

Effect of Upstream Shear on Flow and Heat (Mass) Transfer Over a Flat Plate

2008 ◽  
Author(s):  
Kalyanjit Ghosh ◽  
R. J. Goldstein
Keyword(s):  
Boundary Layer ◽  
Mass Transfer ◽  
Reynolds Number ◽  
Turbulent Boundary Layer ◽  
Flow Direction ◽  
Velocity Ratio ◽  
Leading Edge ◽  
Surface Velocity ◽  
Freestream Velocity ◽  
Inner Region

A parametric study is conducted to investigate the effect of wall shear on a two-dimensional turbulent boundary layer. The shear is imparted by a moving belt, flush with the wall, translating in the flow direction. Velocity and mass transfer experiments have been performed for four surface-to-freestream velocity ratios (0, 0.38, 0.52, 0.65) with a Reynolds number based on the momentum thickness between 770 and 1776. The velocity data indicate that the location of the ‘virtual origin’ of the turbulent boundary layer ‘moves’ downstream towards the trailing edge of the belt with increasing surface velocity. The highest velocity ratio represents a case which is responsible for the removal of the inner region of the boundary layer. Mass transfer measurements downstream of the belt show the presence of a local minimum in the variation of the Stanton vs. Reynolds number for the highest velocity ratio. Downstream of this minimum, approximately 1 cm from the leading edge of the mass transfer plate, the characteristics of the turbulent boundary layer are restored and the data fall back on the empirical variation of the Stanton number with Reynolds number.

Turbulence measurements around a mild separation bubble and downstream of reattachment

1996 ◽  
Vol 322 ◽  
pp. 297-328 ◽  
Author(s):  
Amy E. Alving ◽  
H. H. Fernholz
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Pressure Gradient ◽  
Boundary Layers ◽  
Outer Layer ◽  
Large Scale ◽  
Reverse Flow ◽  
Separation Bubble ◽  
Reynolds Stresses ◽  
Inner Region

This paper describes the behaviour of a turbulent boundary layer on a smooth, axisymmetric body exposed to an adverse pressure gradient of sufficient strength to cause a short region of mean reverse flow ('separation’). The pressure distribution is tailored such that the boundary layer reattaches and then develops in a nominally zero pressure gradient. Hot-wire and pulsed-wire measurements are presented over the separated region and downstream of reattachment. The response of the turbulence quantities to separation and to reattachment is discussed, with emphasis on the relaxation behaviour after reattachment. Over the separation bubble, the response is characteristic of that seen by other workers: the Reynolds stresses in the inner region are reduced and stress peaks develop away from the wall. At reattachment, the skewness of the fluctuating wall shear stress vanishes, as it is known to do at separation. After reattachment, the outer-layer stresses decay towards levels typical of unperturbed boundary layers. But the inner-layer relaxation is unusual. As the viscous wall stress increases downstream of reattachment, the recovery does not start at the wall and travel outward via the formation of an ‘internal’ layer, the process observed in many other relaxing flows. In fact, the inner layer responds markedly more slowly than the outer layer, even though response times are shortest near the wall. It is concluded that the large-scale, outer structures in the turbulent boundary layer survive the separation process and interfere with the regeneration of Reynolds stresses in the inner region after reattachment. This behaviour continues for at least six bubble lengths (20 boundary-layer thicknesses) after reattachment and is believed to have profound implications for our understanding of the interaction between inner and outer layers in turbulent boundary layers.

Effect of Upstream Shear on Flow and Heat (Mass) Transfer Over a Flat Plate—Part II: Mass Transfer Measurements

2010 ◽  
Vol 132 (10) ◽  
Author(s):  
K. Ghosh ◽  
R. J. Goldstein
Keyword(s):  
Boundary Layer ◽  
Mass Transfer ◽  
Reynolds Number ◽  
Turbulent Boundary Layer ◽  
Flat Plate ◽  
Heat Mass Transfer ◽  
Stanton Number ◽  
Freestream Velocity ◽  
Belt Speed ◽  
Inner Region

Mass transfer measurements on a flat plate downstream of a belt moving in the same direction of the freestream study the effect of the upstream shear on the heat (mass) transfer for four belt-freestream velocity ratios. With an increase in this ratio, the “virtual origin” of the turbulent boundary layer “moves” downstream toward the trailing edge of the belt. This is verified from the variation of the Stanton number versus the Reynolds number plots. As the “inner” region of the boundary layer is removed for a belt speed of uw=10 m/s (freestream velocity uin≈15.4 m/s), a corresponding local minimum in the variation of the Stanton number is observed. Downstream of this minimum, the characteristics of the turbulent boundary layer are restored and the data fall back on the empirical variation of Stanton with Reynolds number.

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