Free-Wake Hover Flow Prediction with a Hybrid Potential/Navier-Stokes Solver

This paper describes the development of an overset/hybrid code with a new free-wake capability. The method combines an overset version of the well-known HELIX-I code with the TURNS Navier-Stokes code. The TURNS code provides the surface viscous flow while HELIX-I provides accurate wake convection for the prediction of the induced power. The method is grid point efficient since the Eulerian solver is not burdened with resolving the shed wake. Examining the flow about the AH-64A rotor operating in the stall regime demonstrates the necessity of using a Navier-Stokes solver near the blade surface. A free-wake computation of the XV-15 tilt-rotor was performed to evaluate the new free-wake capability of the code. Comparison of the predicted tip vortex trajectory with experiment was excellent. Application of the combined overset/hybrid procedure to predict the hover performance of the UH-60A rotor provides the first validation of this new free-wake method.