A Technique to Control the Decay of Freestream Turbulence for Transitional Flow Simulations

The use of transition models in Reynolds-averaged Navier-Stokes solvers is usually accompanied by high values of the eddy viscosity at the inlet, due to the role of this quantity in controlling the decay of freestream turbulence, a critical factor in the behavior of these models. This paper presents a new approach to control the decay of freestream turbulence that avoids setting high values for the inlet eddy viscosity. The proposed method is based on the modification of the dissipation term of the turbulence model only in the freestream, ensuring that the original formulation of the model is retained in regions where viscous effects are significant. The new technique is tested on the flow over a flat plate and around a NACA 0012 airfoil and a 6:1 prolate spheroid, using the gamma-Re-theta model. The results show that the method allows for reductions of up to three orders of magnitude of the inlet eddy viscosity, without disturbing the solution of the original model for cases with low or moderate turbulence intensity. The method requires the Kato-Launder stagnation point correction to be used in the underlying turbulence model, due to the strong influence of the turbulence production limiter on the location of transition.