Hybrid CFD for Rotor Hover Performance Prediction

This paper presents recent advances in a fully coupled hybrid free vortex wake and computational fluid dynamics (CFD) solution methodology for hovering rotor performance calculations. The hybridization process effectively separates the tasks of computing the blade surface flow and the wake convection. The blade loading solution is obtained using a Reynolds-averaged Navier-Stokes (RANS) solver on a relatively small grid surrounding the blade to minimize numerical diffusion, while the far-field wake region is solved using a vorticity-embedding (VE) potential flow solution with a force-free vortex wake. The VE methodology is an unusual type of CFD-based vortex-lattice method, which eliminates the need for expensive Biot-Savart law computations by solving the full-potential equations with an auxiliary velocity field representation of the Lagrangian vortex wake. The VE methodology alone can be applied to the hover problem and is shown to provide robust and accurate predictions, at least for attached flow cond itions. The hybrid approach is more general and can predict a detailed flow field around the rotor blades. The acc uracy of these methods is demonstrated by comparison with UH-60A model rotor performance, wake and loads data.