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Experiments on wave breaking in stratified flow over obstacles

Published online by Cambridge University Press:  26 April 2006

Ian P. Castro  and
William H. Snyder
Ian P. Castro
Affiliation:
Mechanical Engineering Department, University of Surrey, Guildford, Surrey, GU2 5XH, UK
William H. Snyder
Affiliation:
Atmospheric Sciences Modeling Division, Air Resources Laboratory, National Oceanic and Atmospheric Administration, Research Triangle Park, NC 27711, USA On assignment to the Atmospheric Research and Exposure Assessment Laboratory, US Environmental Protection Agency, Research Triangle Park, NC 27711, USA.
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Abstract

Towing-tank experiments on linearly stratified flow over three-dimensional obstacles of various shapes are described. Particular emphasis is given to the parameter regimes which lead to wave breaking aloft, the most important of which is the Froude number defined by Fh = U/Nh, where U, N and h are the flow speed, the Brunt–Väisälä frequency and the hill height, respectively. The effects of other parameters, principally K (= ND/πU, where D is the fluid depth) and the spanwise and longitudinal aspect ratios of the hill, on wave breaking are also demonstrated. It is shown that the Froude-number range over which wave breaking occurs is generally much more restricted than the predictions of linear (hydrostatic) theories would suggest; nonlinear (Long's model) theories are in somewhat closer agreement with experiment. The results also show that a breaking wave aloft can exist separately from a further recirculating region downstream of the hill under the second lee wave, but that under certain circumstances these can interact to form a massive turbulent zone whose height is much greater than h. Previous theories only give estimates for the upper critical Fh, below which breaking occurs; the experiments also reveal lower critical values, below which there is no wave breaking.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 255 , October 1993 , pp. 195 - 211
Copyright
© 1993 Cambridge University Press

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