Analysis of acoustic field of primary vortex pairing in subsonic plane mixing layers using kirchhoff method

In order to expand the calculation and analysis of an acoustic field generated by vortex pairing, the subsonic planar mixing layer vortex pairing is studied with numerical method. Direct numerical simulation (DNS) is employed to extract the acoustic source, the two-dimensional frequency domain and time domain Kirchhoff methods are applied to extrapolate the far-field radiated sound, while the frequency domain method is employed to investigate the sound radiation from the twice vortex pairings. The frequency domain and time domain Kirchhoff methods are different in some degree, but the computation results compared with the DNS show that they reach a similar high order of accuracy. An analysis with frequency domain Kirchhoff method reveals clearly that each acoustic mode of the twice vortex pairings corresponds to the vortex rolls and pairings respectively. Using the frequency domain method's good performance of computation and analysis, this paper further studies the influence of inflow instability waves with different phases on the acoustic field of vortex pairings, and exhibits that the dominant mode plays an important role in the acoustic field.