Modeling of Variable Surface Roughness Effects in Turbulence Models for Rotorcraft Applications

The goal of this Phase II program is to develop a simulation tool to estimate the aerodynamic effects of variable surface roughness, such as from the surface abrasion of helicopter rotor blades and the protective coatings that are applied to counteract it. The modeling is based on a displacement of origin methodology, within the k-omega turbulence model frameworks. Our initial investigations suggest that this method is effective in non-equilibrium boundary layers. Additionally we will implement and develop intermittency based transition models. We will work with OpenFoam and OVERFLOW CFD solvers which are widely used in the rotorcraft, and aerodynamics community. We expect to develop a state-of-the-art simulation tool for rotor blade drag estimation, and demonstrate capabilities through rotor simulations. The work plan consists of implementation and extension of the roughness models, in addition to development of a general capability for user defined measures of surface roughness. The effort includes verification and validation and also includes experiments to develop validation for configurations that are relevant to the rotorcraft application roughness strips and representative pressure gradients. A transition model will be implemented, with verification and validation using available transition data on turbine geometries.