A simple sound source for temporally-developing mixing layers

Applying Lighthill's acoustic analogy equation to temporally-developing mixing layers, we derived a direct relation between the near-field work by pressure fluctuation and the far-field sound. The sound radiation predicted by the new model was compared to the direct numerical simulation, and the results agreed well for the sound radiation from different vortex dynamics in mixing layers: roll-up, pairing (or tearing), 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.