Acoustics of a two-dimensional compact jet impinging normally onto a flat plate

Vortex sound is revisited for two-dimensional compact jets. The interaction s between the flow and the rigid boundaries of the nozzle are included. Jet s with steady upstream conditions and with imposed forcing are considered. A multipole expansion for the acoustic radiation is derived by the method o f matched asymptotic expansion. The processes are carried out to higher ord er to obtain the quadrupole impingement sound in addition to the leading mo nopole. The emitted sound is found to be related to the vortical flow motio n and the scattering of the incoming forcing from the nozzle interior. The flow motion is simulated incompressibly using a point vortex model. The dis cretization of the continuous vortex shedding is carefully treated to fulfi l the Kutta condition and to eliminate spurious sound radiation. Numerical calculations are given for both free and forced jets. For small forcing, th e leading monopole is weak and, under some circumstances, the quadrupole so und can be dominant.