Generation of acoustic waves in a two-dimensional forced shear layer

The generation of small amplitude acoustic waves in a two-dimensional forced shear layer is studied numerically. The formulation is based on the concept of the Bernoulli enthalpy. The flowfield is represented by division into two parts: the vortical and the compressible flows. Each field is treated separately and coupled with the other through the Bernoulli enthalpy. Acoustic waves are identified as unsteady compressible motions free of vorticity. Results indicate that the dynamics of the vortical flow plays a decisive role in determining the characteristics of acoustic radiation. The formation of large vortical structures and subsequent dynamic processes act as quadrupole sources. The motions of coherent flow structures contribute significantly to sound generation.