MetroLaser has developed a Computational Fluid Dynamics (CFD) based simulation tool to estimate the aerodynamic effects of variable surface roughness, such as from 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-ω turbulence model frameworks. Additionally, we also implemented and developed intermittency based transition models. These models were implemented in OpenFoam and OVERFLOW CFD solvers, which are widely used in the rotorcraft and aerodynamics community. This is a state-of-the-art simulation tool for rotor blade drag estimation, and we have demonstrated its capabilities through rotorcraft simulations. This work also consisted of implementation and extension of roughness models, in addition to development of a general capability for user defined measures of surface roughness. Further, it included verification and validation and also included experiments to develop validation for configurations that are relevant to the rotorcraft application – roughness strips and representative pressure gradients. A transition model was implemented, with verification and validation using available transition data on turbine geometries.
The roughness models that we have developed are modular, and enable interfacing with commercial and governmental CFD codes. The ability of this tool to calculate drag contributions from complex rough surfaces with discontinuities has significant commercial implications not only in the computation of helicopter parasitic drag, but also for turbine/compressor blades, wind turbine blades, heat exchangers, etc., that are subjected to harsh environments or fouling in an uneven manner. The developed model contains procedures to map user-specified properties that define arbitrary rough surfaces onto the computational geometry. The modules can also be made available as standalone CFD solvers or as user defined subroutines capable of being integrated into a variety of CFD packages.