Recent Improvements to a Hybrid Method for Rotors in Forward Flight

A hybrid Navier-Stokes/full potential solver has been developed for the efficient prediction of three-dimensional unsteady viscous flow phenomena that occur over helicopter rotors in forward flight. The method combines a Navier-Stokes analysis near the blade, modeling the viscous flow and near wake with a potential flow analysis in the far field, model ing inviscid isentropic flow. A grid motion module has been developed to account for the blade motion and elastic deformations. Free and prescribed wake models have been developed to account for the tip vortex effects once the vortex leaves the viscous flow region and enters the potential flow region. Sample results are presented for a two-bladed AH-1G rotor in descent and for a UH-60A rotor in high-speed forward flight. Comparisons with experiments, flight test data, and other numerical simulations are given