Acoustic Modeling Using the Aeroacoustic Wave Equation Based on Pierce's Operator

The capabilities of an aeroacoustic wave equation based on Pierce’s operator (AWE-PO) for modeling subsonic flow-induced sound and for sound prediction are investigated. The wave equation is applied to an isothermal two-dimensional mixing layer computed by direct numerical simulation. In contrast to a direct numerical simulation, providing the acoustic fluctuations directly, the simulations based on Lighthill’s wave equation and the AWE-PO rely on a hybrid workflow to predict the generated sound field. Special attention is put on the interpretation of the right-hand side of both wave equations. Comparing the terms on the right-hand side in Lighthill’s theory and AWE-PO suggests a source amplitude for AWE-PO that is 90% smaller. This reduction is attributed to the filtering property of the material derivative. Finally, the results of the acoustic far-field pressure are compared. It is shown that the radiated sound field’s directivity, propagation, and convection effects are well captured for both wave equations. The computations using Lighthill’s equation and AWE-PO are found to provide acoustic intensities within 1.8 dB from the reference direct numerical simulation. This error is comparable with the errors reported for Lighthill’s equation in previous studies