Simulations of stably stratified flow past two spheres at Re = 300

Abstract

Flows past two spheres immersed in a horizontally moving, linearly-stratified fluid are investigated at a moderate Reynolds number of 300. Characterisation of flow patterns considers representative geometrical configurations defined by varying both the distance between the spheres and their relative orientation to the free stream direction. Simulations are performed on unstructured meshes chosen to accurately resolve the dynamics of fluids in regions close to the spheres for Froude numbers Fr ∈ [0.25, ∞]. Results illustrate the evolution of boundary layers, separation, and the wakes interaction under the influence of a gravity induced buoyancy force. Computations utilise a limited area, nonhydrostatic model employing Non-oscillatory Forward-in-Time (NFT) integration based on the Multidimensional Positive Definite Advection Transport Algorithm (MPDATA). The model solves the Navier-Stokes equations in the incompressible Boussinnesq limit, suitable for describing a range of mesoscale atmospheric flows. Results demonstrate that stratification progressively dominates the flow patterns as the Froude number decreases and that the interactions between the two spheres' wakes bear a resemblance to atmospheric flows past hills.