Numerical simulation of vortical wake flow of a micro-vortex generator by using non-equilibrium Eddy Viscosity Model

Abstract

Reynolds Averaged Navier-Stokes (RANS) simulations using Non-equilibrium Eddy Viscosity Model as proposed by Akira Yoshizawa has been implemented into k-omega SST model of Menter to simulate for flow around a single rectangular Micro-Vortex Generator placed on a flat plate, skewed at three different angles (10 o, 16 o & 23o). Conventional two-equation models perform rather poorly for flows that are not in near-equilibrium state. These turbulence models are based on single-time-scale schemes. Flow past a vortex generator produces tip vortices which are highly non-equilibrium in nature. Hence, the Non-equilibrium eddy viscosity model as proposed by Yoshizawa et al. has been employed in this study. Yoshizawa’s Non-equilibrium eddy viscosity model takes into account a non-stationary or non-equilibrium effect in time scale of turbulence. This is synthesized by combining several characteristic time scales; mean-strain, mean-vorticity and also frame-rotation effect on dissipation rate equation. This modification results in reduction of eddy viscosity in swirling flows. Experimental and CFD database of Yao and Lin has been taken as a reference case for the present study. GAMBIT is used to generate structured mesh for the entire computational domain and simulations are performed in OpenFOAM in which simpleFOAM, a steady state solver for incompressible, turbulent flow; is employed. Computational results indicate that the characteristics of the tip vortex for the MVG are much better predicted by employing this Non-equilibrium eddy viscosity model compared to the original k-omega SST model of Menter. Non-equilibrium eddy viscosity model reduces the estimation of turbulent eddy viscosity in the vortex core region compared to the k-omega SST model which leads to better prediction of vortex features of the MVG cases. Vortex path, both in vertical and lateral directions obtained from Non-equilibrium eddy viscosity model follow the same trend as that of k-omega SST model. The...