Far-field evolution of turbulence-emitted internal waves and reynolds number effects on a localized stratified turbulent flow.

摘要

In this dissertation, internal waves (IWs) and turbulence in the stably stratified ocean are studied via a series of numerical simulations. First of all, internal wave beams that are representative of high-mode internal tide originated from the ocean topography and constituent element of turbulence-emitted IWs are studied via direct numerical simulations (DNS), with an emphasis on their reflection at the sea surface as modelled by a free-slip rigid lid. Nonlinear effects due to wave-wave interaction, such as mean flow and harmonics, are investigated; in particular, the amplitude of the wave-driven Eulerian mean flow is found to match the theoretical prediction of an inviscid weakly nonlinear theory. The IW beams can also degrade at late time of reflection due to parametric subharmonic instability. Subsequent particle tracking is performed based the DNS dataset, in an attempt to examine the mass transport driven by the reflecting IW beams. These fully nonlinear computations reveal a horizontal dispersion of ocean tracers with a dispersivity scaling with O(A4), where A is the steepness of the IW beam, while small-amplitude analysis accurate to O(A2) suggests an exact cancellation of Eulerian mean flow due to wave-wave interaction and the wave-driven Stokes drift.