CORRELATIONS OF ROTOR/WAKE-AIRFRAME INTERACTION MEASUREMENTS WITH FLOW VISUALIZATION DATA

Wind tunnel tests were conducted on an idealized rotor-airframe configuration in forward flight. High resolution unsteady surface pressure measurements were obtained along the top of the airframe in order to examine the interaction effects of the rotor and wake on the airframe. In conjunction with these pressure measurements, flow visualization tests were conducted in order to identify flow field features which cause the interaction effects. Results indicate that there are three prominent interactions with the airframe. In order of significance these are: blade passage effect, tip vortex effect and vortex sheet effect. These interactions determine, to a large degree, the overall pressure distribution on the airframe surface, and hence the airframe unsteady airloads. It is crucial that future aerodynamic interaction codes have the ability to correctly predict these effects, especially when high disk loadings and small rotor-airframe spacings are being considered in a rotorcraft design.