Characteristics of the pressure fluctuations generated in turbulent boundary layers over rough surfaces

2019 ◽  
Vol 883 ◽  
Author(s):  
Liselle A. Joseph ◽  
Nicholas J. Molinaro ◽  
William J. Devenport ◽  
Timothy W. Meyers
Keyword(s):  
Boundary Layers ◽  
Rough Surfaces ◽  
Pressure Fluctuations ◽  
Turbulent Boundary Layers ◽  
Image Position

Conditional statistics of Reynolds stress in rough-wall and smooth-wall turbulent boundary layers

1981 ◽  
Vol 108 ◽  
pp. 363-382 ◽  
Author(s):  
M. R. Raupach
Keyword(s):  
Surface Roughness ◽  
Boundary Layers ◽  
Rough Surfaces ◽  
Reynolds Shear Stress ◽  
Roughness Element ◽  
Threshold Level ◽  
Turbulent Boundary Layers ◽  
Quadrant Analysis ◽  
Normal Velocity ◽  
The Third

Quadrant analysis has been used to investigate the events contributing to the Reynolds shear stress in zero-pressure-gradient turbulent boundary layers over regularly arrayed rough surfaces of several different densities, and over a smooth surface. By partitioning the stress into ejections, sweeps, and inward and outward interactions, it is shown that sweeps account for most of the stress close to rough surfaces, and that the relative magnitude of the sweep component increases both with surface roughness and with proximity to the surface. The sweep-dominated region delineates a ‘roughness sublayer’ with a depth of up to several roughness element heights, in which the turbulence characteristics depend explicitly on the roughness. In the remainder of the inner (or constant-stress) layer, and in the outer layer, the flow obeys familiar similarity laws with respect to surface roughness.The difference ΔS0 between the fractional contributions of sweeps and ejections to the stress is shown to be well related everywhere to the third moments of the streamwise and normal velocity fluctuations. Experimental proportionalities are established between the third moments and δS0, and are shown to agree with predictions made from cumulant-discard theory.The time scale for the passage of large coherent structures past a fixed point, T, is assumed proportional to the mean time between occurrences in a specified quadrant of an instantaneous stress u'w’ at least H times the local mean stress u'w’, where H is a threshold level. For both the ejection and sweep quadrants and for any choice of H, it is found that T scales with the friction velocity u* and the boundary-layer thickness δ, such that Tu*/δ is invariant with change of surface roughness.

scholarly journals Eddy Viscosities and Mixing Lengths for Turbulent Boundary Layers on Flat Plates, Smooth or Rough

1988 ◽  
Vol 32 (04) ◽  
pp. 229-237
Author(s):  
Paul S. Granville
Keyword(s):  
Boundary Layers ◽  
Rough Surfaces ◽  
Equations Of Motion ◽  
Reynolds Numbers ◽  
Turbulent Boundary Layers ◽  
Flat Plates ◽  
Low Reynolds Numbers ◽  
Low Reynolds ◽  
Similarity Laws

Algebraic formulas are derived here for the eddy viscosities and mixing lengths of turbulent boundary layers on flat plates. The effect of low Reynolds numbers, especially on rough surfaces, is included. The formulas are based on the similarity laws and the equations of motion. Both smooth and rough surfaces are considered. The agreement with Klebanoff's measurements is excellent.

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