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The interaction of waves and a turbulent current: waves propagating against the current

Published online by Cambridge University Press:  20 April 2006

P. H. Kemp  and
R. R. Simons
P. H. Kemp
Affiliation:
Department of Civil and Municipal Engineering, University College London. Gower Street, London WC1E 6BT
R. R. Simons
Affiliation:
Department of Civil and Municipal Engineering, University College London. Gower Street, London WC1E 6BT
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Abstract

The results of an experimental study of the interaction between waves and a current propagating in the same direction, have been reported by Kemp & Simons (1982). This paper describes the second part of the study, and considers the case of waves propagating against the current. Tests were performed in a laboratory flume with smooth and rough beds, and velocity measurements were made with a directionally sensitive laser anemometer as described in the previous paper. Analysis, including ensemble averaging of velocities and surface elevation, was performed by an on-line computer.

Results indicate that the rate of wave attenuation is greatly increased by the addition of an opposing current, and reduced by a following current. Wave profiles remain closely described by Stokes second-order theory; orbital velocities are also found to be in agreement with a second-order wave theory modified to take account of the presence of the current.

Certain results described occur regardless of the relative directions of current and wave. Mean velocities in the upper flow increase in the direction of the wave generator for increasing wave height. This suggests that the current is enhancing the wave-induced mass transport. Near the bed the velocity profiles so change that above the rough bed the current is retarded by the wave motion. In the logarithmic layer over the smooth bed velocities are increased with increasing wave height. However, all changes to velocity profiles have to be carefully interpreted, as the sidewall boundary layer decreases in thickness with even the smallest wave superimposed on the current.

Turbulence intensities and Reynolds stresses near the rough bed are increased by the presence of the waves, most strongly in a layer two roughness heights above bed level, where fluctuations are periodic and effected by vortices ejected from the roughness troughs. Above this level, and over the smooth bed, turbulence levels are similar to those for the currents alone.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 130 , May 1983 , pp. 73 - 89
Copyright
© 1983 Cambridge University Press

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