Resolving Turbulent Wakes

Abstract

Resolving the turbulent statistics of bluff-body wakes is a challenging task. Frequently, the streamwise grid point spacing approaching the vortex exit boundary is sacrificed to gain near full resolution of the turbulent scales neighboring the body surface. This choice favors the solution strategies of direct numerical and large-eddy simulations (DNS and LES) that house spectral-like resolving characteristics with inherent dissipation. Herein, two differencing stencils are tested for approximating four forms of the convective derivative in the DNS and LES formulations for incompressible flows. The wake spectral characteristics and conventional parameters are computed for Reynolds numbers Re=200 (laminar wake) and Re=3900. These tests demonstrated reliable stability and spectral-like accuracy of compact fifth-order upwinding for the advective derivative and fourth-order cell-centered Pade´ (with fourth-order upwinding interpolation) for the Arakawa form of the convective derivative. Specifically, observations of the DNS computations suggest that best results of the wake properties are acquired when the inertial subrange of the spectral energy is fully resolved at the grid-scale level. The LES solutions degraded dramatically only when the fifth-order upwind stencil resolved the spanwise periodic turbulence. Although the dynamic subgrid-scale model showed strong participation on the instantaneous level, its spectral contributions were negligible regardless of the chosen grid-scale scheme.