ASA 127th Meeting M.I.T. 1994 June 6-10

5aSA9. Mean flow effects on the vibroacoustic behavior of a plate backed by a cavity in light and heavy fluids.

Franck Sgard

Noureddine Atalla

Jean Nicolas

G.A.U.S., Univ. of Sherbrooke, Sherbrooke, PQ J1K 2R1, Canada

The purpose of this work is to present a general formulation dealing with the vibroacoustic behavior of a baffled plate, immersed on one side in a mean flow and coupled on the other side to a rectangular cavity with arbitrary wall impedances. The plate is excited by a point force, a plane wave convected by the mean flow, or a turbulent boundary layer. The formulation is based on a finite element method for the calculation of the transverse vibrations of the plate. Fluid loading on each side of the plate is taken into account through an impedance matrix approach. The plate--cavity impedance matrix is calculated using a boundary element method. The amount of computation is decreased by using a two indices Green's function for the rigid cavity. The external impedance matrix accounting for mean flow, is calculated using the extended form of Kirchhoff's integral equation and a boundary element method. This formulation is compared with a finite element approach for the calculation of the acoustic field inside the cavity. The mean flow effects are investigated through the calculation of different vibroacoustic indicators like the mean-square velocity of the plate, the internal and external acoustic radiated power, the radiation efficiency of the plate inside the cavity and the transmission loss of the plate. Coupling mechanisms are explained in terms of added mass, stiffness, and damping.