MODEL FOR ROTOR TIP VORTEX AIRFRAME INTERACTION PART 3 - VISCOUS-FLOWON AIRFRAME

The behavior of vortex systems in the vicinity of solid surfaces is a matter of intense interest in rotorcraft aerodynamics, as well as in m any other areas of fluid dynamics. We consider the viscous flow on a s implified model of a helicopter airframe due to a helicopter rotor tip vortex both experimentally and computationally. As the tip vortex app roaches the airframe, the computational results predict the genesis of a region just upstream of the main vortex, characterized by reversed flow and rapid growth in size. The experiments clearly show evidence o f such a region under the tip vortex in the region predicted by the co mputations and at roughly the same time. The secondary vorticity field in the computations is of a sign opposite to the vorticity associated with the tip vortex. Results for the streamline patterns and vorticit y field during the genesis of the secondary eddy are presented and com pared with experimental flow visualization results.