LES OF SEPARATED FLOWS AT MODERATE REYNOLDS NUMBERS APPROPRIATE FOR TURBINE BLADES AND UNMANNED AERO VEHICLES

Abstract

Flows over airfoils and blades in rotating machinery, for unmanned and micro-aerial vehicles, wind turbines, and propellers consist of a laminar boundary layer near the leading edge that is often followed by a laminar separation bubble and transition to turbulence further downstream. Typical RANS turbulence models are inadequate for such flows. Direct numerical simulation (DNS) is the most reliable but is also the most computationally expensive alternative. This work assesses the capability of LES to significantly reduce the resolution requirements for such flows and still provide results of DNS quality. Two flows are considered. A flow over a flat plate with suitable velocity boundary conditions away from the plate to produce a separation bubble and a 2-D flow on a NACA-0012 airfoil. By employing several different codes we conclude that accurate LES are possible using O(1%) of the DNS resolution and that the numerical dissipation plays a significant role in LES of such flows.