Vortex Interactions in the Wakes of Rotors in Hover

In recent experiments[1] on a two-bladed rotor in low axial climb it was observed that vortices shed from each of the blades interacted significantly at approximately one rotor radius below the rotor disk plane. This phenomenon was verified by numerical solutions of the rotor wake for the same experimental conditions[2]. The purpose of this paper is to extend the calculations to the case of hover and to the case of three and four blades. A lifting line is used to model each blade and a fully unsteady computation of the motion of each tip-vortex is carried out using a highly accurate Adams-Moulton method to advance the vortices. The vortex-vortex interaction is particularly complicated for the case of three and four bladed rotors where several vortices are observed to become locally intertwined. It is suggested that this kind of behavior can be explained on the basis of classical vortex dynamics.