Turbulence production in flow over a wavy wall

Abstract

over a wavy wall 257 Abstract Measurements of the spatial and time variation of two components of the velocity have been made over a sinusoidal solid wavy boundary with a height to length ratio of 2a/2 = 0.10 and with a dimensionless wave number of ~ + = (27t/2) (v/u*)= 0.02. For these conditions, both intermittent and time-mean flow reversals are observed near the troughs of the waves. Statistical quantities that are determined are the mean streamwise and normal velocities, the root-meansquare of the fluctuations of the streamwise and normal velocities, and the Reynolds shear stresses. Turbulence production is calculated from these measurements.The flow is characterized by an outer flow and by an inner flow extending to a distance of about c~-1 from the mean level of the surface. Turbulence production in the inner region is fundamentally different from flow over a flat surface in that it is mainly associated with a shear layer that separates from the back of the wave. Flow close to the surface is best described by an interaction between the shear layer and the wall, which produces a retarded zone and a boundary-layer with large wall shear stresses.Measurements of the outer flow compare favorably with measurements over a flat wall if velocities are made dimensionless by a friction velocity defined with a shear stress obtained by extrapolating measurements of the Reynolds stress to the mean levels of the surface (rather than from the drag on the wall).

TRPIV investigation of space-time correlation in turbulent flows over flat and wavy walls

“…For the canonical turbulent boundary layer flow, coherent structures such as quasistreamwise vortex [29][30][31] are considered as the key to the production and sustaining of turbulence [32,33]. For flows over a wavy wall, shear layers [34,35] are the sources of energy and Reynolds stress, as observed by Buckles et al [34]. Turbulence in these regions is controlled by diffusion of turbulent kinetic energy from shear layers [36].…”

“…Unlike the canonical TBL over a flat wall, the definition of TBL thickness over a wavy wall is subtle. We consider the midpoint of the waviness in the wall-normal direction as the origin of the boundary layer, like reference [35]. Then velocity profiles were wave-averaged at 5 locations, i.e., 1 crest, 2 through and 2 midway.…”

Direct Numerical Simulation and Filtering of Turbulent Flows over Model Rough Surfaces

“…U m is the cross-sectional average velocity defined by the total volume flow rate divided by the average channel cross section BxH and the Reynolds number based on H and U m is set close to 6760 for all cases and close to that of the experiments of Hudson et al 11) , DNS of Maass & Schumann 10) , LES of Henn & Sykes 14) and Calhoun & Street 15) and twice as large as Cherukat et. al.…”

“…Since there are considerable amount of information both numerical and experimental, on flows over wavy walls, (Buckles,Hanratty & Adrian 9) , Maass & Schumann 10) , Hudson, Dykhno & Hanratty, 11) , De Angelis, Lombardi & Banerjee 12) , Cherukat et al 13) ; Henn & Skyes 14) ; Calhoun & Street 15) ) that can be made use of in verification and interpretation, we use a sinusoidal waviness as the basic geometry to construct more complex and general geometry. In many rough-surface flow investigations, angular roughness elements such as strip bars and blocks have been used as simplified models (e.g.…”

Turbulent flow over a wavy surface: Stratified case

“…CS1 used, for the purposes of comparisons with experimental results, an effective friction velocity that was derived from experimental results by extrapolating Reynolds stress from the outer flow to a "mean" lower boundary. For more details on how this is done in an experimental setting, see Hudson et al [1996].…”