Experimental Study on the Effects of Geometrical Misalignment and Shape Modification on Ring Tone

Abstract

The sound produced by placing a coaxial ring downstream of a circular jet is called a ring tone. It is reinforced by a phase-matching feedback process through the processes of the growth of vortex rings in the jet shear, its impingement on the ring, the upstream propagation of pressure waves and the perturbation of the jet shear layer at the nozzle exit. In this study, we investigated the effects of geometrical misalignment and shape modification on the ring tone for the first time. In particular, the effects of changes in the angle of attachment of the ring to the nozzle exit, its radial position relative to the rotational axis of the round jet, the surface roughness of the inner wall of the nozzle exit, and the diameter and thickness of the ring on the ring tone are shown. These misalignments and shape modifications result in different Sound Pressure Level (SPL) distributions, depending on angular deviation, radial position deviation, and surface roughness height. Smoke visualization of the baseline ring tone was also conducted. The surface roughness muffles the peak sound, depending on the impingement length, and the ring tone occurs when the inner diameter of the ring d_i satisfies the condition d_i/(d₀ + 2δ_j) < 1.28 where d₀ is the inner diameter of the nozzle exit and δ_j is the thickness of the jet shear layer.