Sound radiation from an airfoil encountering an oblique gust in its plane of motion

An evaluation is conducted of the acoustic field radiated when an airfoil encounters a gust in the plane of motion, with a view to the prediction of helicopter tail rotor noise. The analysis is based on the unsteady thickness noise theory of Glegg (1987). Sound radiation is shown to be dominated by the transient effect of the blade tip moving into the velocity deficit, so that the effects of blade rotation are not important.