Authors: S Nakagawa Y Na T J Hanratty
Publish Date: 2003/09/09
Volume: 35, Issue: 5, Pages: 422-436
Abstract
Measurements of turbulence with laser Doppler velocimetry LDV are compared for turbulent flows over a flat surface and a surface with sinusoidal waves of small wavelength The wavy boundary was highly rough in that the flow separated The Reynolds number based on the halfheight of the channel and the bulk velocity was 46000 The wavelength was 5 mm and the height to wavelength ratio was 01 The rootmeansquares of the velocity fluctuations are approximately equal if normalized with the friction velocity This can be explained as a consequence of the approximate equality of the correlation coefficients of the Reynolds shear stress Calculations with a direct numerical simulation DNS are used to show that the fluid interacts with the wall in quite different ways for flat and wavy surfaces They show similarity in that large quadrant 2 events in the outer flow for both cases are associated with plumes that emerge from the wall region and extend over large distances Measurements of skewness of the streamwise and wallnormal velocity fluctuations and quadrant analyses of the Reynolds shear stresses are qualitatively similar for flat and wavy surfaces However the skewness magnitudes and the ratio of the quadrant 2 to quadrant 4 contributions are larger for the wavy surface Thus there is evidence that turbulent structures are universal in the outer flow and for quantitative differences in the statistics that reflect differences in the way in which the fluid interacts with the wall
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