Prediction of Scattered Broadband Shock-Associated Noise

A mathematical model is developed for the prediction of broadband shock-associated noise in the presence of an airframe body. Model arguments are dependent on the vector Green’s function of the linearized Euler equations, steady Reynolds-averaged Navier–Stokes solutions, and the two-point cross-correlation of the equivalent source. The equivalent source is dependent on steady Reynolds-averaged Navier–Stokes solutions of the jet flow that capture the nozzle and airframe geometry. Contours of the time-averaged streamwise velocity component and turbulent kinetic energy are examined with varying airframe position relative to the nozzle exit. Propagation effects are incorporated by approximating the vector Green’s function of the linearized Euler equations. This approximation involves the use of ray theory and an assumption that broadband shock-associated noise is relatively unaffected by the refraction of the jet shear layer. A nondimensional parameter is proposed that quantifies the changes of the broadband shock-associated noise source with varying jet operating condition and airframe position. Scattered broadband shock-associated noise possesses a second set of broadband lobes that are due to the effect of scattering. Presented predictions from an overexpanded jet demonstrate relatively good agreement compared to a wide variety of measurements.