Sound generation by the scattering of vortical waves from a convected vortex

The interaction between the vortical waves carried by the upstream flow and the downstream large-scale vortex widely exists in the field of aeronautical and aerospace engineering. Although there are many works on vortex-wave interaction, to this day, it is unclear whether the interaction between vortical waves, as transverse waves, and vortices can generate acoustic waves, as longitudinal waves, and whether the sound generation by the scattering of vortical waves exists in vortical flows. The present work addresses the sound generation by vortical scattering from typical vortical flows. A convected isentropic vortex model has been established to align with realistic flow characteristics, and the governing equations involved in the sound generation by vortical scattering from such vortical flow have been derived. A numerical model framework is proposed to systematically investigate the vortical scattering in a vortical flow. The finite-difference method has been used to numerically simulate the physical process of sound generation by vortical scattering from a convected vortex. Based on Helmholtz decomposition, the propagation properties of each component of the perturbation waves in the scattered field have been obtained, directly verifying the existence of acoustic waves produced by the scattering of vortical waves in vortical flows. In addition, dimensionless parameters that play a key role responsible for the vortical scattering have been identified: vortex strength, length-scale ratio, convective Mach number, and freestream Mach number, with a particular focus on the influence of vortex strength and length-scale ratio on the scattered acoustic fields.