Hybrid Reynolds-Averaged Navier-Stokes/Large-Eddy Simulation Closure for Separated Transitional Flows

The numerical prediction of transition from laminar to turbulent flow has proven to be an arduous challenge for computational fluid dynamics, with few approaches providing routine accurate results within the cost confines of engineering applications. The recently proposed gamma-R epsilon(theta) transition model shows promise for predicting attached and mildly separated boundary layers in the transitional regime, but its accuracy diminishes for massively separated flows. In this effort, a new turbulence closure is proposed that combines the strengths of the local dynamic kinetic energy model and the widely adopted gamma-R epsilon(theta) transition model using an additive hybrid filtering approach. This method has the potential for accurately capturing massively separated boundary layers in the transitional Reynolds number range at a reasonable computational cost. Comparisons are evaluated on several cases, including a transitional flat plate, NACA 63-415 wing, and circular cylinder in crossflow. The new closure captures the physics associated with a separated wake (circular cylinder) across a range of Reynolds numbers from 10 to 2 million (2 x 10(6)) and performed significantly better in capturing performance and flowfield features of engineering interest than existing turbulence models. The transitional hybrid approach is numerically robust and requires less than 2% extra computational work per iteration as compared with the baseline Langtry-Menter transition model.