Turbulent dissipation in the boundary layer of precession-driven flow in a sphere

Abstract

The energy dissipation in a uniform vorticity flow, such as the flow in a precessing spheroid or the one associated with the earth’s free core nutation, is mainly confined to the boundary layers. However, the thinness of the boundary layer renders it difficult to study the energy dissipation in the turbulent regime, either in laboratory experiments or through direct numerical simulations. Here, we use a local Cartesian model to study the energy dissipation in the boundary layer of a precessing sphere when the flow becomes turbulent, contrasting it with the laminar case. We compute the evolution of the boundary layer over time at individual co-latitudes based on direct numerical simulations using the computational fluid dynamics solver Nek5000. We then estimate the total global dissipation by summing up individual contributions. A comparison with known analytical results in the laminar case validates this approach. We briefly discuss the applications to the lunar and the earth’s core cases.