Experimental Study of a Jet-Driven Helmholtz Oscillator

Abstract

This paper describes an experimental study of a Helmholtz resonator driven by a round jet passing through it. This device, dubbed the jet-driven Helmholtz oscillator (JDHO), is a rigid chamber with two round openings located coaxially in two opposite walls, through which a jet is allowed to pass across the chamber. At certain jet velocities, jet instabilities couple with the Helmholtz resonance to produce very powerful chamber-pressure oscillations at a frequency slightly higher than the chamber Helmholtz frequency. The amplitude of these pressure oscillations may reach values of up to 5.6 times the jet dynamic pressure. Simultaneously, the exiting flow pulsates at the same frequency with an amplitude of up to 60 percent of the exit jet velocity, and a loud sound is emitted. The thrust of the present study was twofold: to determine the optimum range of geometrical parameters producing the maximum magnitudes, and to identify the mechanisms underlying the oscillator operation.