Developments and applications of hybrid RANS-LES methods for wide-speed-range flows

Abstract

The growing demands of aerospace industry require accurate prediction of unsteady flow details. Current Reynolds averaged Navier-Stokes (RANS) methods are unable to provide dynamic loads for unsteady turbulent flows at high Reynolds numbers, such as massively separated flows past complex geometries. Large eddy simulation (LES) and direct numerical simulation (DNS) are still too expensive for engineering applications. Hybrid RANS-LES methods, combining near-wall RANS regions and outer LES regions, are the most promising techniques for unsteady turbulent flows in engineering. First of all, a general introduction to several categories of hybrid RANS-LES methods was given to discuss their basic ideas and characteristics. Then, the development history of detached-eddy simulation (DES) type methods was presented together with the influences of high-accuracy time-marching methods, spatial discretization schemes and proper numerical dissipation. For both mechanism studies and engineering applications, multiple cases at Mach numbers varying from 0.1 to 20 show that hybrid RANS-LES methods are an ideal choice for the prediction of turbulent flow in engineering. Hybrid RANS-LES methods are capable of predicting complex features involved in massive separation. Future improvement includes the promotion in computation efficiency and embedded RANS/LES strategy for detailed flow past small local component. Big potential also exists for hybrid RANS-LES methods in areas closely related to unsteady flow, such as dynamic stall, combustion and aero-elastics/acoustics/optics.