Novel boundary integral formulation for blade-vortex interaction aerodynamics of helicopter rotors

A direct panel method based on a novel boundary integral formulation for the velocity potential is presented and applied to helicopter rotors experiencing blade-vortex interaction. It avoids the numerical instabilities arising in the standard direct panel method in case of blade/wake impingement. This aerodynamic formulation yields a unified approach for the calculation of free-wake evolution and the blade-pressure field; it is fully 3-D, includes body-thickness effects, and can be applied to blades with arbitrary shape and motion. Blade-pressure predictions and the corresponding acoustic fields correlate well with wind-tunnel test data for helicopter rotors in descent flight, in which severe blade-vortex interaction occurs.