A Strategy for Very Large Eddy Simulation of Complex Turbulent Flows

Abstract

This paper describes a strategy for the very large eddy simulation (VLES) of complex turbulent flows, such as flows in the aircraft engine combustors or flows around the rotorcrafts. The large scales of turbulence are directly calculated; the effects of the rest unresolved scales are approximated by the eddy viscosity models evolved from the state-ofthe-art models used in the Reynolds-averaged Navier-Stokes (RANS). The dependent variables and governing equations are based on the concept of temporal filtering. The contents of both resolved and unresolved scales are regulated by the width of the filter. In this approach, the dependent variables and governing equations will naturally evolve from RANS to VLES and further towards LES (large eddy simulation) when the width of the temporal filter is decreased from the turbulent integral time scale to its fraction and all the way towards the Taylor micro time scale. We refer this strategy as the partially resolved numerical simulation (PRNS). The main feature of PRNS is that its constitutive equations for the unresolved turbulence have no relationship with the mesh size, hence formally grid independent; its subscale models have the nature of a non-linear dynamic system capable of effectively controlling the subscale stresses to perform VLES with a relatively coarse grid. In addition, its implementation to a turbulent CFD code is straightforward.