A Simple Model For Study Of Sound Generation Mechanism In Mixing Layers

Applying Lighthill's acoustic analogy equation to temporally-developing mixing layers, we derived a direct relation between the near-field dynamics, in terms of pressure work, and the far-field sound. The sound radiation predicted by the new model was compared to the direct numerical simulation result, and they agreed well in all stages of vortex dynamics development in mixing layers: roll-up, pairing, merging, saturation, and viscous damping. Using the new formulation, we explained the mechanism for sound generation from the considered flow, and depicted general topological structures for the distribution of sound sources. Though the dynamics is different for vortex roll-up and vortex pairing, the same mechanism for sound generation is suggested by similar topological structures of the sound sources defined here.