Numerical Simulations of Laminar and Turbulent Mixing Layers behind a Thin Airfoil

Abstract

Steady and unsteady simulations of two-stream incompressible mixing layers with a fixed velocity ratio of 2, generated at the trailing edge of a NACA0006 airfoil in 2D and 3D domains are investigated in laminar and turbulent flow regimes. Numerical simulations are first conducted to study the behavior of mixing layers in laminar flow regimes. Effects of high-speed side free-stream Reynolds number and temperature are investigated and considered in relation to prediction of the developing behavior of the 2D mixing layer. Unsteady behavior of the 3D case in a range of free-stream Reynolds numbers is also explored and visualized by using parallel computation. Having shown that shape factors in both streamwise and spanwise directions increase with increasing free-stream velocity, it is found that for the 2D case raising the high-speed side flow temperature reduces the stability of the velocity profiles. The rate of reduction is accelerated by employing higher Reynolds numbers. Turbulent mixing layers behind the airfoil are studied numerically by employing parallel computation for Reynolds-Averaged Navier-Stokes (RANS)-based models for 2D and 3D grids. In addition, large eddy simulation (LES) is conducted to explore 3D behavior of the turbulent mixing layer. Effects of inflow turbulence intensity as well as Reynolds number are investigated by examining growth rate parameters. Although the applied turbulence models predict almost the same trends of spreading rate and velocity distribution, the SST model in 2D cases and the LES model in 3D cases gave the best results. It is also found that shape factor decreases with increasing turbulence intensity. Furthermore, increasing the Reynolds number did not show any significant influence on this trend. In the spanwise direction, the shape factor variation does not follow this trend.