Simulation of Transition with a Two-Equation Turbulence Model

Abstract

This paper demonstrates how well the A>co turbulence model describes the nonlinear growth of flow instabilities from laminar flow into the turbulent flow regime. Viscous modifications are proposed for the A>co model that yield close agreement with measurements and with direct numerical simulation results for channel and pipe flow. These modifications permit prediction of subtle sublayer details such as maximum dissipation at the surface, k ~ y2 as y —> 0, and the sharp peak value of k near the surface. With two transition specific closure coefficients, the model equations yield a realistic description of a transitional incompressible flat-plate boundary layer. A new concept known as the numerical roughness strip is introduced that permits triggering transition at a desired location. A series of transitional boundary-layer applications, including effects of surface heat transfer, pressure gradient and freestream Mach number, verify that the numerical roughness strip is very effective in triggering transition and that flow in the transitional region is realistically described.