Computation of sound radiating from engine inlets

A hybrid method has been developed to calculate sound radiation from turbofan engine inlets. Given the acoustic source at an interface near the fan, the method solves the full three-dimensional, time-dependent Euler equations in the near field and passes the solution to a moving-surface Kirchhoff method for far-field predictions. The Kirchhoff method enables one to limit the size of the computational domain where the essential acoustic signals are captured accurately by a high-order accurate flow solver and then to extrapolate these signals to the far field exactly only within the discretization error on the Kirchhoff surface. The steady flowfield is required by the hybrid approach and a high-order accurate multigrid method has been implemented to enhance convergence of steady-state calculations. The computations are all carried out on parallel processors using essentially high-performance Fortran language. Results indicate very good agreement with available numerical and analytical solutions.