Influence of the nature of the gas in the edge-tone phenomenon

The present study deals with the edge-tone phenomenon. Gas injection is performed through a nozzle with a 0.6×20 mm2 cross-section and two possible lengths of 20 and 50 mm. The effect of the nature of the injected gas on both the flow arrangement and sound frequency is investigated by a coupled experimental and numerical approach. In the experiments, special attention is paid to the definition and experimental measurement of the velocity at the nozzle outlet for the three injected gases. If the head losses in the injection duct are correctly taken into account, no influence of its length is obtained, which contradicts the results published recently by Ségoufin et al. [2004. Experimental investigation of the flue channel geometry influence on edge-tone oscillations. Acta Acustica 90, 966-975]. Injections of air, Neon, and CO2 into air are then successively considered. The numerical simulations are based on the two-dimensional resolution of the unsteady Navier-Stokes equations, in association with a two-fluid physical model. A homogeneous approach is used to treat the behaviour of the mixture composed of the two gases. The density of the injected gas is found to have a significant influence on the flow pattern and the sound frequency, which suggests that the fluid density should be included in the relations that give the frequency of the edge tone instability. Moreover, it is shown that the jet oscillation frequencies obtained both numerically and experimentally can be derived from a theoretical analysis of the Kelvin-Helmholtz instability, on condition that the parabolic shape of the gas velocity at the nozzle outlet is taken into account.