Dynamics of Unsteady Strait and Sill Flow

摘要

The dynamics of steady and unsteady channel flow over large obstacles is studied analytically and numerically in an attempt to determine the applicability of classical hydraulic concepts to such flows. The study is motivated by a need to understand the influence of deep ocean straits and sills on the abyssal circulation. The discussion centers around the time-dependent adjustment to the sudden obtrusion of an obstacle into a uniform initial flow and the oscillatory upstream forcing of a steady flow over topography. For nondispersive (nonrotating or semigeostrophic) flow, nonlinear adjustment to obstacle obtrusion is examined using a characteristic formulation and numerical results obtained from a Lax-Wendroff scheme. The findings indicate that the initial flow can be totally blocked, partially blocked, or unblocked depending upon the height of the obstacle. The blockage is accomplished through breaking waves that alter the potential vorticity of the flow at a rate proportional to the differential rate of energy dissipation along the line of breakage.