Investigation of rotor tip vortex interactions with a body

Abstract

Experiments were conducted to examine rotor tip vortex interactions with a body in low-speed forward flight. Unsteady pressure measurements were made at points along the top and around the circumference of the body surface. Flow visualization of the rotor wake was performed using the wide-field shadowgraph method. Considerable insight into the tip vortex interaction processes was obtained by correlating the pressure loads with the vortex trajectories as they approached, distorted, and impinged on the body surface. Unsteady potential flow theory was explored as a means of predicting the unsteady pressure loads on the body surface, using prescribed tip vortex trajectories measured from flow visualization. The results have shown that the process of tip vortex interaction with a body can be divided into three regimes: 1) close tip vortex/body interactions, which is an inviscid flow regime; 2) vortex/surface impingement; and 3) postvortex/surface impingement; the latter involves viscous effects. The results have also shown that the pressures at points on the body exhibited a high sensitivity to tip vortex convection speed and location, which makes the general prediction of such interactional phenomena difficult with existing rotor/airframe interaction models.