Large eddy simulations around a sphere using unstructured grids

A computational study of unsteady, separated, low and high Reynolds number flows is made using a second-order accurate, cell-centered finite volume method on unstructured grids. The simulations include large-eddy simulation turbulence modeling based on a classical Smagorinsky subgrid-scale model. For the high Reynolds number simulations, wall shear stress is modeled by using the instantaneous logarithmic law of the wall. All the cases simulated are assumed to be fully turbulent, since the turbulence model is active over the entire surface of the sphere. The main objective of this work is to study the flow about a sphere at a Reynolds number of 1.14×10⁶ which is in the supercritical range. Comparisons are made with experimental results by Achenbach and flow visualizations by Taneda. Predictions of the drag, mean pressure and mean skin-friction distributions along the sphere are in good agreement with experiments. The wake structure of the supercritical case is substantially changed compared to the subcritical flows with the wake in the supercritical case dominated by shedding of hairpin-like vortices. Three dimensional stereographic movies are also made using Ensight 7.6 to gain a deeper insight into wake-flow structure.