Noise generation by gas jets in a turbulent wake

Radiated noise is generated when gas discharges from an underwater orifice into a turbulent wake. Few quantitative studies under controlled conditions have been reported, however, and the mechanism of this noise generation is not well understood. This paper presents measurements of noise radiated by gas jets exhausting into a turbulent wake under controlled conditions in the test section of a 48-in. diam water tunnel. Acoustic-measurements in the frequency range 6–45 kHz were made with a directional hydrophone mounted in a water-filled tank attached to one side of the tunnel test section. A turbulent wake was generated by a water speed of 9.1 m/sec flowing past a strut-mounted cigar-shaped body. Nitrogen gas was discharged at various flow rates into the turbulence through two different nozzle plates attached to the aft end of the wake-generating body. For the range of parameters used in these experiments, results indicate that radiated noise is primarily a function of orifice radius and the turbulence parameters, and only secondarily of gas flow rates. One possible mechanism for the generation of this noise may be related to a critical Weber number.