Velocity measurements of airframe effects on a rotor in a low-speed forward flight

Abstract

Aerodynamic interactions between the rotor and the airframe of a rotorcraft can have severe effects and are difficult to predict analytically. To attack this problem, the velocity field of a two-bladed rotor has been measured in a wind tunnel with and without an airframe model in proximity. The periodic and time-averged velocity fields were measured using a laser velocimeter in planes both parallel to and above and below the rotor tip path plane at an advance ratio of 0.1 and a rotor tip Mach number of 0.29. The data were shown to be free of tunnel wall effects. The effect of including the cylindrical airframe model were measured. For the geometry studied, airframe influence on the rotor flowfield was mostly confined to the front half of the rotor disc. Hub effects were noticeable, even with the minimal-sized hub used. Strong vortex interaction effects were observed using strobed laser sheet flow visualization and measured using laser velocimetry.