Simultaneous skin friction and velocity measurements in high Reynolds number pipe and boundary layer flows

Baidya, R., Baars, W. J., Zimmerman, S., Samie, M., Hearst, R. J., Dogan, E., Mascotelli, L., Zheng, X., Bellani, G., Talamelli, A., Ganapathisubramani, B., Hutchins, N., Marusic, I., Klewicki, J. and Monty, J. P. (2019) Simultaneous skin friction and velocity measurements in high Reynolds number pipe and boundary layer flows. Journal of Fluid Mechanics, 871, 377-400. (doi:10.1017/jfm.2019.303).

Abstract

Streamwise velocity and wall-shear stress are acquired simultaneously with a hot-wire and an array of azimuthal/spanwise-spaced skin friction sensors in large-scale pipe and boundary layer flow facilities at high Reynolds numbers. These allow for a correlation analysis on a per-scale basis between the velocity and reference skin friction signals to reveal which velocity-based turbulent motions are stochastically coherent with turbulent skin friction. In the logarithmic region, the wall-attached structures in both the pipe and boundary layers show evidence of self-similarity, and the range of scales over which the self-similarity is observed decreases with an increasing azimuthal/spanwise offset between the velocity and the reference skin friction signals. The present empirical observations support the existence of a self-similar range of wall-attached turbulence, which in turn are used to extend the model of Baars et al. (J. Fluid Mech., vol. 823, p. R2) to include the azimuthal/spanwise trends. Furthermore, the region where the self-similarity is observed correspond with the wall height where the mean momentum equation formally admits a self-similar invariant form, and simultaneously where the mean and variance profiles of the streamwise velocity exhibit logarithmic dependence. The experimental observations suggest that the self-similar wall-attached structures follow an aspect ratio of in the streamwise, spanwise and wall-normal directions, respectively.

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Contributors

Author: B. Ganapathisubramani

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