Development of a CFD-based Hover Performance Prediction Tool for Engineering Analysis

This paper concerns the development of a second-generation implementation of the vorticity embedding method for the prediction of rotor hover performance. The basic method, encoded in the HELIX-IA code, is an Eulerian- Lagrangian, Computational Fluid Dynamics (CFD)-based procedure that utilizes either a lifting-line or liftingsurface aerodynamic model for the rotor blades. In this paper, the basic method is hybridized with the TURNS Reynolds Averaged Navier-Stokes (RANS) code. The TURNS code provides the surface viscous flow while HELIX-IA provides accurate wake convection for the prediction of the induced power. The method is grid point efcient since the viscous solver is not burdened with resolving the entire shed wake. The importance of recent enhancements to the basic HELIX-IA methodology is demonstrated by a very good comparison of predictions (performance, loading and wake trajectory) with available model scale data. Application of the new hybrid option of HELIX-IA to the UH-60A Black Hawk rotor provides a first demonstration of this coupled free-wake method. Convergence of the hybrid/coupled method is good, showing the basic viability of the approach. Hybrid computations show a strong dependence of wake trajectory on tip loading, and the need for tip grid improvement in order to attain better accuracy.