The best whistler: a cavitating tip vortex

TL;DR

This paper uncovers the mechanism behind the mysterious 'vortex singing' in cavitating tip vortices, revealing it is triggered by near-end sound sources and explaining its occurrence within a specific cavitation number range.

Contribution

It introduces a theoretical framework that explains the vortex singing phenomenon and accurately predicts its conditions, resolving a long-standing scientific mystery.

Findings

Identified the sound generation mechanism involving breathing mode waves.

Predicted the specific cavitation number range for vortex singing.

Validated the theory with historical experimental data.

Abstract

The discrete tone radiated from a cavitating tip vortex, known as "vortex singing", was first recognized in 1989, but its sound generation mechanism has remained a mystery for over thirty years. In this letter, by means of the correction for the cavitation bubble dynamics and the dispersion relation of cavity interfacial waves, we found that after the far-end disturbances propagate upstream, the whistling vortex should be triggered by near-end sound sources, the breathing mode waves. Further utilizing the theoretical solutions for singing lines and the potential singing cavitation number with frequency, we accurately identified all available tests for seeking the vortex singing over the past three decades, answering a long-standing perplexity: why such a best whistler is able to appear only within a narrow range of the cavitation number.