Noise Generation by Gas Jets in a Turbulent Wake

Radiation noise is generated by the interaction of gas jets with turbulent liquid. Although this phenomenon has long been known, the mechanism of noise generation and its functional relationship to important parameters are not well understood. No experimental studies of gas jet-turbulence interaction noise under controlled conditions can be found in the literature. To remedy this paucity of experimental data, measurements of this phenomenon were made in the 1.22 m diameter test section of the Garfield Thomas Water Tunnel. Gas was exhausted from the aft end of the strut-mounted test body into the turbulent wake. A directional hydrophone, mounted outside the flow in a water-filled tank on one side of the test section, was used to make one-third-octave-band acoustic measurements in the frequency range 5 - 50 kHz. By varying the gas exhaust orifice diameters, gas flow rates, and water speeds, the interdependence of the important parameters to radiated noise was determined. For the range of variables used in these experiments, the radiated noise is primarily a function of the ratio of orifice diameter to turbulence length scale, and only secondarily, a function of gas flow rates. Analysis of the results indicate that noise generated by the formation, division, coalescence, and collapse of bubbles can be related to the critical Weber number of the flow. (Author)