Computation of acoustic propagation in two-dimensional sheared ducted flows

Most aeroacoustic noise-prediction methods rely on an acoustic analogy feat uring a propagation equation associated with source terms. These models wer e mainly applied to computation of acoustic far fields radiated by simple f ree flows like jets. The assumption is made in many formulations that the r adiated acoustic field is not perturbed by the shear flow giving rise to th e noise sources. These acoustic analogies thus do not provide a full descri ption of acoustic/flow interactions. The Lilley equation was introduced to account, to a certain extent, for mean shear effects on propagation. More r ecently, this problem has been treated by making use of the linearized Eule r equations, which are more flexible and more adequate for numerical simula tions. As several types of modes are supported by the Euler equations, prob lems linked to their coupling have to be considered. It Is then necessary t o investigate acoustic field computations in complex Rows. Our aim in the p resent article is to validate the wave operator associated with linearized Euler equations. Numerical tests deal with propagation in two-dimensional s heared ducted Rows. Results are compared with other solutions deduced from analytical developments and direct numerical simulations, This study shows that the linearized Euler operator may be used to account for mean effects on wave propagation in the presence of sheared ducted flows, Processes that are specifically considered are 1) convection effects on axial disturbance s, 2) refraction effects on oblique wave generation, and 3) source radiatio n effects on propagation in sheared flows.