A review of the theory of trailing edge noise

A critical review is presented of the literature on the theory of the generation of sound by the interaction of low Mach number turbulent flow with the edge of a semi-infinite rigid plate. Three distinct approaches to the subject are identified, consisting of theories based on (1) Lighthill's acoustic analogy, (2) the solution of special, linearized hydroacoustic problems and (3) ad hoc aerodynamic source models. It is shown that, when appropriately interpreted, all relevant theories produce essentially identical predictions in the limit of very small Mach numbers. In none of the theories, however, are the implications of the Kutta condition discussed, nor of the effect of forward flight and source motion relative to the trailing edge. Accordingly this review includes an outline of a redevelopment of the theory which gives a unified view of the problem, exhibits the significance of the various approximations, and incorporates the effect of mean motion and of the Kutta condition.