An Analytical Method for Predicting Rotor Wake Geometry

Abstract

An analytical method for predicting the distorted geometry of a helicopter rotor wake is described. The development of this method is ultimately directed toward providing a more accurate aerodynamic theory for computing the instantaneous rotor flow field and associated blade airloads. It is shown that: (1) realistic self‐induced distortions of a rotor wake represented by numerous discrete vortex elements can be computed by application of the classical Biot‐Savart law and numerical integration techniques and (2) by dividing the wake into a series of near and far wake regions, the computation requirements which have previously prohibited the use of such an analysis as a cost‐effective engineering tool can be appreciably reduced. Sample comparisons of analytical and experimental wake geometries of a rotor in forward flight are presented and indicate the ability of the analysis to predict the characteristic distortion features of the wake.