Achievements in the numerical modeling of fan noise radiation from aero-engines

A numerical approach based on the solution of convected wave equations in the frequency domain is applied to the prediction of fan noise radiation from realistic engine configurations at realistic operating conditions. Fully three-dimensional computations based on the acoustic velocity potential at Helmholtz numbers up to 30 are carried-out in order to simulate the sound transmission through a scarfed inlet in the presence of a spliced liner. A verification of the method capability in featuring the modal scattering in the presence of rigid splices is carried out by comparing present results with analytical and numerical results available in the literature. In order to avoid the treatment of the vortex sheet shed from the edge of the bypass duct, a wave model for the acoustic pressure based on the Lilleyʹs third-order wave operator is used for the aft noise radiation from the exhaust. Again, a fully three-dimensional computation is carried-out for a Helmholtz number equal to 30 and results are compared to analytical solutions available in the literature for an idealized flow configuration. Finally, the effects of a more realistic mean flow are investigated by evaluating the refractive effects due to a mixing-layer velocity profile.