A Hybrid RANS/LES Turbulence Model for use in the Simulation of Turbulent Separated Flows

Abstract

Currently, there exists a lack of confidence in the computational simulation of turbulent separated flows at large Reynolds numbers. The most accurate methods available are too computationally costly for use in engineering applications. Using concepts borrowed from large-eddy simulation (LES), a two-equation Reynolds-averaged Navier-Stokes (RANS) turbulence model is modified to simulate the turbulent wakes behind bluff bodies. This modification involves the computation of one additional scalar field, adding very little to the overall computational cost. When properly inserted in the baseline RANS model, this modification mimics LES in the separated wake, yet reverts to the unmodified form near no-slip surfaces. In this manner, superior predictive capability may be achieved without the additional cost of fine spatial resolution associated with LES near solid boundaries. Simulations using several modified and baseline RANS models are benchmarked against both LES and experimental data for a circular cylinder wake at Reynolds number 3900. These results reveal substantial improvements using the modified system and appear to drive the baseline wake solution toward that of LES, as intended. Further results include the simulation of the turbulent wake created by the Ground Transportation System (GTS), a simplified tractor-trailer geometry studied extensively by the Department of Energy for use in turbulence model validation.