An Embedded LES-RANS Solver for Aerodynamic Simulations

Abstract

In the current work, we present the development and application of an embedded largeeddy simulation (LES) -Reynolds-averaged Navier Stokes (RANS) solver. The novelty of the present work lies in fully embedding the LES region inside a global RANS region. RANS and LES regions are explicitly coupled through arbitrary mesh interfaces and flow and turbulence quantities are exchanged between them as the solution is advanced. A digital filter method extracting mean flow, turbulent kinetic energy and Reynolds stresses from the upstream RANS interface is used to provide meaningful small scale fluctuations to the LES interface. The framework is developed in the open-source computational fluid dynamics software OpenFOAM. The embedding approach is validated by simulating a spatially developing turbulent channel flow. Thereafter, flow over a surface mounted spanwiseperiodic vertical fence is simulated to demonstrate the importance of DFM and the effect of the location of the RANS-LES interface. In each case, both mean and second-order statistics are compared with the direct numerical simulation (DNS) data from the literature. The streamwise evolution of skin friction coefficient on the wall is compared with the DNS result and the attachment point of the primary recirculation zone behind the fence matches the reference data well. Results indicate that by feeding synthetic turbulence at the LES interface a good match can be obtained for the mean flow quantities. However, in order to obtain a good match for the Reynolds stresses the LES interface needs to be placed sufficiently far upstream, which in the present case was six spoiler-heights before the fence.

Reynolds Stress Structures in the Hybrid RANS/LES of a Planar Channel

“…The interface between the two zones is prescribed by the user and turbulent fluctuations must be generated as a boundary condition for the LES. This interface can be either perpendicular to the wall [18] or parallel [19]. The former is used when near-wall interactions are deemed crucial to the overall flow prediction and the latter when computational power cannot be spared to resolve the boundary layer.…”