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Transcritical shallow-water flow past topography: finite-amplitude theory

Published online by Cambridge University Press:  04 November 2009

G. A. EL ,
R. H. J. GRIMSHAW  and
N. F. SMYTH
G. A. EL*
Affiliation:
Department of Mathematical Sciences, Loughborough University, Loughborough LE11 3TU, UK
R. H. J. GRIMSHAW
Affiliation:
Department of Mathematical Sciences, Loughborough University, Loughborough LE11 3TU, UK
N. F. SMYTH
Affiliation:
School of Mathematics and Maxwell Institute for Mathematical Sciences, University of Edinburgh, The King's Buildings, Mayfield Road, Edinburgh, Scotland EH9 3JZ, UK
*
†Email address for correspondence: G.El@lboro.ac.uk
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Abstract

We consider shallow-water flow past a broad bottom ridge, localized in the flow direction, using the framework of the forced Su–Gardner (SG) system of equations, with a primary focus on the transcritical regime when the Froude number of the oncoming flow is close to unity. These equations are an asymptotic long-wave approximation of the full Euler system, obtained without a simultaneous expansion in the wave amplitude, and hence are expected to be superior to the usual weakly nonlinear Boussinesq-type models in reproducing the quantitative features of fully nonlinear shallow-water flows. A combination of the local transcritical hydraulic solution over the localized topography, which produces upstream and downstream hydraulic jumps, and unsteady undular bore solutions describing the resolution of these hydraulic jumps, is used to describe various flow regimes depending on the combination of the topography height and the Froude number. We take advantage of the recently developed modulation theory of SG undular bores to derive the main parameters of transcritical fully nonlinear shallow-water flow, such as the leading solitary wave amplitudes for the upstream and downstream undular bores, the speeds of the undular bores edges and the drag force. Our results confirm that most of the features of the previously developed description in the framework of the unidirectional forced Korteweg–de Vries (KdV) model hold up qualitatively for finite amplitude waves, while the quantitative description can be obtained in the framework of the bidirectional forced SG system. Our analytic solutions agree with numerical simulations of the forced SG equations within the range of applicability of these equations.

Type
Papers
Information
Journal of Fluid Mechanics , Volume 640 , 10 December 2009 , pp. 187 - 214
Copyright
Copyright © Cambridge University Press 2009

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