Large Eddy Simulations around a Sphere Using Unstructured Grids

Abstract

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 × 10 6 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.

3-D Time-Accurate CFD Simulations of Wind Turbine Rotor Flow Fields

“…A wall function has also been implemented to the PUMA2 code, which was tested with flow over sphere simulations. 18 Further modifications are being performed on PUMA2 in order to improve the code's computational efficiency for LES simulations.…”

“…It uses dynamic memory allocation, thus the problem size is limited only by the amount of memory available on the machine. Large Eddy Simulations (LES) 17 with or without wall models 18 can also be performed with PUMA2.…”

“…A wall model based on an instantaneous logarithmic law of the wall is developed and implemented in PUMA2. 18 For high Reynolds number turbulent flows the log-law approach is used at the first cell away from the solid surface to get the shear stress at the wall. The logarithmic law of the wall, which is obtained by neglecting all terms in the streamwise momentum equation except the Reynolds-stress gradient, can be expressed as:…”

Large Eddy Simulation of the ventilated wave boundary layer

“…The classic Smagorinsky model is widely used, even though more refined models exist, due to its simplicity and relatively easy implementation. Some examples are the earlier mentioned studies by Rudman and Blackburn [1999], Li and Cheng [2001], Liang and Cheng [2005], and Jindal et al [2004].…”

“…With increasing computer power the LES have been used extensively during the last 10–15 years, in studies where detailed information about the turbulence in flow of high Reynolds‐numbers (i.e., where a direct numerical simulation (DNS) is not possible) is needed. Some examples are the detailed study of the turbulence associated with wave breaking [ Christensen , 1998], study of turbulent pipe flow [ Rudman and Blackburn , 1999], lee‐wake scouring of pipeline in currents [ Li and Cheng , 2001], the study of flow and scour below a pipeline in currents [ Liang and Cheng , 2005], flow around a sphere [ Jindal et al , 2004] and turbulent flow in ducts with a free surface [ Broglia et al , 2003]. No detailed study of the turbulent high Re‐number oscillatory boundary layer exists.…”