Acoustic emission by vortex–edge interaction is investigated both theoretically and experimentally. The theory of vortex sound enables us to represent the far-field pressure in terms of the vortex motion near the half-plane edge. It is found that the pressure p depends on the product of an angular factor representing directionality and a time factor representing wave profile. The pressure formula leads to the scaling law $p \propto U^{\frac{5}{2}} L^{-2}$ for the sound emitted by a vortex ring of velocity U, L being the nearest distance of the vortex path to the edge. The sound intensity is proportional to U5 and shows cardioid directionality pattern.
The vortex ring used in the experiment had radius about 4.7 mm and velocity ranging from 29 to 61 m/s. The above scaling law of the pressure and the cardioid directionality of the intensity were reproduced in the experiment with reasonable accuracy. Especially notable is the agreement between the predicted and observed wave profiles. The theoretical profile is determined by the $\frac{3}{2}\,{\rm th}$ time derivative of the volume flux (through the vortex ring) of a hypothetical potential flow around the edge.