Investigation of noise generated by the interactions of coaxial vortex rings

The interactions of coaxial vortex rings are the typical flow in subsonic jets and the significant sources of jet noise. Controlling the acceleration and deceleration of vortex rings during the interactions is critical to noise reduction. Previous studies have shown that the radial acceleration of the weaker ring is the dominant contributor to high-amplitude, low-frequency noise. In this work, the conditions under which this phenomenon occurs and the physical laws that govern it are investigated based on Dyson thin-core vortex ring model. By decomposing the acoustic source into the product of the vortex rings’ axial and radial kinematic parameters, the interactions of vortex rings are analyzed under various initial circulation and radius ratios. A critical initial radius ratio is identified, below which the source term related to the radial acceleration of the weaker ring contributes more to the total noise source than that of the stronger ring. Through quantitative analysis of the vortex ring interaction dynamics, the correlation between the peak value of the noise pulse and the peak values of axial velocity and radial acceleration of the rings is established. Moreover, the reverse motion of the stronger ring can induce an out-of-phase pulse in its corresponding acoustic source term.