Engineering Formulations for Turbulence Modeling of Variable Surface Roughness Effects in Wall-Bounded Flows

The proposed effort has the objective to develop a method for representing the influence of surface roughness on turbulent transport. The method is designed for highly non-equilibrium flows, as occurs on helicopter rotors, and in other engineering applications. It is based on the displacement of origin approach, which is a way to incorporate roughness into Reynolds-averaged Navier-Stokes (RANS) turbulence models via modified boundary conditions: it is our objective to devise an approach that is useable with standard engineering meshes and CFD methods. Further, the methodology also contains a formulation for intermittency, suitable for rough-wall boundary layers, to blend between laminar and fully turbulent states. The model will be validated against experimental data for abruptly changing surface roughness. Additional experiments will be conducted under this SBIR Phase I program to address the type of roughness that is found on rotors operated in harsh environments, and with protective coatings. While the acquired data is directly relevant to this application, it will also be of fundamental, benchmark type.