CALCULATIONS OF INTERACTION OF ACOUSTIC WAVES WITH A TWO-DIMENSIONAL FREE SHEAR LAYER.

The acoustic/vortical interaction in a two-dimensional free shear layer has been studied. The flowfield is represented by division into two parts: the vortical and the compressible flows. Each field is treated separately and linked with the other through the Bernoulli enthalpy. Acoustic waves are identified as unsteady compressible motions free of vorticity. Calculations have been carried out for the flowfields with and without externally imposed disturbances. Preliminary results reported here indicate that the motion of large coherent flow structures contributes significantly to sound generation. In particular, the formation of large structure and subsequent pairing appear globally as a quadrupole source.