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A laboratory study of stratified accelerating shear flow over a rough boundary

Published online by Cambridge University Press:  20 April 2006

S. A. Thorpe
S. A. Thorpe
Affiliation:
Institute of Oceanographic Sciences, Wormley, Godalming, Surrey, U.K.
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Abstract

Experiments are made in which a stratified shear flow, accelerating from rest and containing a level where the direction of flow reverses, is generated over a rough floor. The roughness elements consist of parallel square bars set at regular intervals normal to the direction of flow. Radiating internal gravity waves are generated in the early stages of flow, whilst flow separation behind the bars produces turbulent mixing regions which eventually amalgamate and entirely cover the floor. This turbulent layer spreads vertically less rapidly than the internal waves. Observed features of the waves are compared with those predicted by a model in which the floor is assumed to be sinusoidal, and fair agreement is found for the amplitude, phase and vertical wavenumber of the waves, even when the latter becomes large.

The rate of spread of the turbulent layer depends on the separation of the bars. Some interaction between the turbulence and the internal waves occurs near the edge of the turbulent layer. Wave-breaking is prevalent and the vertical scale of the waves is affected by turbulent eddies. The radiating internal waves are suppressed by replacing the bars by an array of square cubes, but there is continued evidence of features resembling internal waves near the boundary of the turbulent region. Structures are observed which bear some similarities to those found at the foot of the near-surface mixing layer in a lake.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 138 , January 1984 , pp. 185 - 196
Copyright
© 1984 Cambridge University Press

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References

Brown, S. N. & Stewartson, K. 1980 On the algebraic decay of disturbances in a stratified linear shear flow J. Fluid Mech. 100, 811–816.Google Scholar
Dillon, T. M. & Caldwell, D. R. 1978 Catastrophic events in a surface mixed layer Nature 276, 601–602.Google Scholar
Koop, C. G. 1981 A preliminary investigation of the interaction of internal gravity waves with a steady shearing motion J. Fluid Mech. 113, 347–386.Google Scholar
Peltier, W. R., Halle, J. & Clark, T. L. 1978 The evolution of finite amplitude Kelvin-Helmholtz billows Geophys. Astrophys. Fluid Dyn. 10, 53–87.Google Scholar
Perry, A. E., Schofield, W. H. & Joubert, P. N. 1969 Rough wall turbulent boundary layers J. Fluid Mech. 37, 383–413.Google Scholar
Piat, J.-F. & Hopfinger, E. J. 1981 A boundary layer topped by a density interface J. Fluid Mech. 113, 411–432.Google Scholar
Raupach, M. R., Thom, A. S. & Edwards, I. 1980 A wind-tunnel study of turbulent flow close to regularly arrayed rough surfaces Boundary-Layer Met. 18, 373–397.Google Scholar
Thorpe, S. A. 1973 Turbulence in stably stratified fluids. A review of laboratory experiments Boundary-Layer Met. 5, 95–119.Google Scholar
Thorpe, S. A. 1978a On internal gravity waves in an accelerating shear flow. J. Fluid Mech. 88, 623–639.Google Scholar
Thorpe, S. A. 1978b The near-surface ocean mixing layer in stable heating conditions. J. Geophys. Res. 83, 2875–2885.
Thorpe, S. A. 1981 An experimental study of critical layers J. Fluid Mech. 103, 321–344.Google Scholar
Thorpe, S. A. & Hall, A. J. 1980 The mixing layer of Loch Ness J. Fluid Mech. 101, 687–703.Google Scholar
Thorpe, S. A. & Hall, A. J. 1982 Observations of the thermal structure of Langmuir circulation J. Fluid Mech. 114, 237–250.Google Scholar
Thorpe, S. A., Hall, A. J., Taylor, C. & Allen, J. 1977 Billows in Loch Ness Deep-Sea Res. 24, 371–379.Google Scholar
Townsend, A. A. 1968 Excitation of internal waves in a stably stratified atmosphere with considerable wind-shear J. Fluid Mech. 32, 145–171.Google Scholar
Woods, J. D 1968 Wave-induced shear instability in the summer thermocline J. Fluid Mech. 32, 791–800.Google Scholar