The effect of forward flight on the diffraction radiation of a high speed jet

This paper describes a theoretical modelling of the effect of aircraft flight on the diffractional generation of sound which occurs when shear layer turbulence convects at high speed past a trailing edge. This is relevant to the study of noise problems associated with blown flaps, powered lift and aerodynamic shielding devices. The analysis is conducted for a two-dimensional configuration at arbitrary subsonic flight velocity. It is concluded that in the absence of a Kutta condition at the trailing edge, the effect of flight results in a forward arc amplification of the diffraction radiation through a single Doppler factor on the linear acoustic pressure field. The forward arc lift in the field shape disappears when a Kutta condition is imposed. In all cases the intensity of the diffraction radiation at 90° to the flight path is diminished by forward motion of the aircraft.