Semester 2, Week 4: Prof Caroline Terquem, University of Oxford

Academic webpage

Title: Turbulent damping of fast oscillations by a convective flow

Abstract:Traditional mixing-length models describe tidal dissipation in convective flows as a large-scale oscillation damped by an effective turbulent viscosity that is artificially reduced when the oscillation period is much shorter than the convective turnover time.  This yields dissipation rates far below observational constraints. From first principles, we have shown that this picture should be reversed for high-frequency oscillations: the fluctuations correspond to the tidal oscillation and the mean shear arises from large convective eddies. This framework yields an energy exchange rate coupling the oscillation’s Reynolds stress with the convective shear but it does not, on its own, specify whether energy flows into or out of the oscillation. Three-dimensional Rayleigh-Benard simulations with a radiative free surface show that the oscillations in fact transfer energy to the mean convective flow, at the rate\sim u’^{2}/t_{conv}, demonstrating strong correlations between fluctuation velocities and the large-scale shear. Within the simple equilibrium-tide framework, this damping mechanism reconciles theory with observed dissipation.

Location: Maths Lecture Theatre B