Large Eddy Simulation of Rotating Finite Source Convection

Abstract

Numerical simulations of turbulent convection under the influence of rotation will help understand mixing in oceanic flows. Though direct numerical simulations (DNS) can accurately model rotating convective flows, this method is limited to small scale and low speed flows. A large eddy simulation (LES) with the Smagorinsky subgrid scale model is used to compute the time evolution of a rotating convection flow generated by a buoyancy source of finite size at a relatively high Rayleigh number. Large eddy simulations with eddy viscosity models have been used successfully for other rotating convective flows, so the Smagorinsky model is a reasonable starting point. These results demonstrate that a LES can be used to model larger scale rotating flows, and the resulting flow structure is in good agreement with DNS and experimental results. These results also demonstrate that the qualitative behavior of vorticies which form under the source depend on the geometry of the flow. For source diameters that are small compared to the size of the domain, the vortices propagate away from the source. On the other hand, if the ratio of source diameter to domain size is relatively large, the vortices are constrained beneath the source. Though the results are qualitatively similar to a direct numerical simulation (DNS) and other LES, in this simulation the flow remains laminar much longer than the DNS predicts. This particular flow is complicated by the turbulence transition between the convective plume and the quiescent ambient fluid, and an eddy viscosity model is inadequate to accurately model this type of flow. In addition, the Smagorinsky model is not consistent in a noninertial reference frame. Thus the Smagorinsky model is not the optimal choice for this type of flow. In particular, the estimation model has demonstrated better results for other types of rotating flows and is the recommended subgrid scale model for future work.