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Examination of v-velocity fluctuations in a turbulent channel flow in the context of sediment transport

Published online by Cambridge University Press:  26 April 2006

T. Wei  and
W. W. Willmarth
T. Wei
Affiliation:
Department of Mechanical and Aerospace Engineering, Rutgers University, Piscataway, NJ 08855, USA
W. W. Willmarth
Affiliation:
Department of Aerospace Engineering, University of Michigan, Ann Arbor, MI 48109-2140, USA
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Abstract

This paper is a report on the mechanism of turbulent momentum transport normal to the wall in a turbulent wall-bounded flow. The objective of this study is to examine the ‘background’ turbulent flow field as a first step toward understanding suspended sediment transport. Specifically, the hypothesis that fine grain particles can be kept in suspension through a net upward momentum flux in a turbulent boundary layer is examined. The net momentum flux can arise if the probability density distribution of the fluctuating v–signal is positively skewed; i.e. the positive v–fluctuations are predominantly of large amplitude and short duration while the negative v-fluctuations are of small amplitude and long duration. High-resolution, two-component laser-doppler anemometer measurements of the v-velocity component in a fully developed turbulent water channel flow were examined spanning a Reynolds number range of 3000 to 23000. Averages of these signals demonstrate that, for very small particles, there is net upward momentum flux in the range y+ > 30, while there is a net downward momentum flux in the range 10 [les ] y+ [les ] 30. Preliminary results which categorize the normal velocity according to quadrants of motion are also included.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 223 , February 1991 , pp. 241 - 252
Copyright
© 1991 Cambridge University Press

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