A SEMIEMPIRICAL HIGH-SPEED ROTOR NOISE PREDICTION TECHNIQUE

A semiempirical technique to predict high-speed noise of helicopter main rotors is discussed. This technique uses an existing data base, the properties of the equations governing the flow field, and empirical relationships to account for the changes in gross weight, blade chord and the blade rotational tip Mach number. The technique is verified through an application to full-scale flyover noise data and full-scale in-flight noise data. Hover test results for a model rotor are used to predict the noise levels for forward flight and are compared with wind tunnel test data. In addition, results of flow field investigations to study the effects of blade design parameters on high-speed noise and to extend the prediction technique are presented. These results are based on the flow field calculations made by using a three-dimensional, quasi-steady, full potential transonic analysis developed by NASA.