A numerical study on the tidal residual flow
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A fundamental mechanism of generation of the tidal residual flow, the steady or quasi-steady flow induced in the tidal current system, is studied by numerical methods. The model basin is a very simple one, a rectangular basin of 5m×10m of constant depth and with a cape of 4 m length jutting out at a right angle from the center of the longer side wall. This basin has the same topography as that studied byYanagi (1976) by means of the hydraulic model experiments.
The steady, circular, horizontal current is found to be induced through the following processes. Horizontal friction at the coast makes the vorticity of vertical component in the oscillating flow. Self-interaction of this flow causes the vorticity transfer to the steady flow in frequency domain. This vorticity transfer is confined in the narrow coastal boundary layer. The steady flow advects the transferred vorticity and makes itself develop fully wide over the bay. In other words, there are two kinds of ‘cascade-up’, one with regard to time scale and the other with regard to horizontal space scale.
When the tidal range, the tidal period and the horizontal eddy viscosity change under the condition that the model geometry is fixed, the nondimensional parameter which controlls the steady flow is found to be the Reynolds number of the oscillating flow.
KeywordsReynolds Number Vorticity Steady Flow Eddy Viscosity Tidal Period
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