Vector Aeroacoustics for a Uniform Mean Flow: Acoustic Intensity and Acoustic Power

Abstract

Acoustic vectors, such as acoustic velocity and acoustic intensity, have advantages over acoustic scalars in showing the detailed propagation path of acoustic energy. In this paper, acoustic vector fields around monopole and dipole sources in uniform mean flow are computed and visualized. Computational results reveal that acoustic intensity fields do not satisfy the feature of the convective amplification, and the directivity pattern of the acoustic intensity is highly dependent on the source type and the mean flow Mach number. Analytical and numerical results indicate that the acoustic power output from a monopole source is always conservative, but the acoustic power output from a dipole source is nonconservative in a uniform mean flow because there is a conversion between the acoustic energy and the vortical energy. Acoustic power output from uniformly moving sources in a quiescent acoustic medium is compared with that from the corresponding stationary sources in a uniform mean flow. The results indicate that the acoustic power output from the monopole sources is nearly the same, but the acoustic power output from the dipole sources is not equivalent in these two cases, and the deviation becomes significant with the increase in the mean flow Mach number.