New numerical method for predicting aero-mechanical behaviors of a rotor hovering at close proximity to inclined flat surface

To predict I.G.E. hover performances of a rotor operating above a non-uniform ground surface, a practical numerical method is developed based on the combined free-wake and panel methods, where the most important feature is an ability to determine a blade flapping motion to be consistent with a deformed wake structure. The boundary surface is substituted for quadratic panels, each of which is approximated by four-sided straight-line vortex segments with unknown strength. The blades are replaced by the lifting lines with a constant circulation and the wake structure is represented by deformed helical vortices lines trailed from the blade tips. The spatial arrangement of tip vortices is determined repeatedly by virtue of the non-penetration conditions at the ground surface and when the converged wake geometry is obtained, the blade flapping motion is calculated using the averaged induced velocity distribution on the rotor disc. Iterative numerical processes are executed until both the wake geometry and the blade flapping motion are converged simultaneously and interactively. In this paper, after a brief description of the numerical procedure, we introduce typical numerical results obtained for the rotor hovering above the uniformly inclined flat surface and clarify unique dependencies of wake geometry, flowfield arm the rotor and the blade flapping motion on the ground inclination angle and the rotor height.