Preliminary Experimental Investigation of the Simple Source Theory for Jet Noise

One of the authors [J. Acoust. Soc. Amer. 30, 318 (1958); Aerodynamic Noise Symp., Loughborough Univ. of Technol. (1970), Paper A7] and H. S. Ribner [Advan. Appl. Mech. 8, 103 (1963)] have proposed a simple source theory for jet noise. The simple source, in the simplest form of the theory, is proportional to the second time derivative of the hydrodynamic pressure within the jet. Using the working hypothesis that the correlation length (eddy size) for a region of fluid radiating sound at frequency f is inversely proportional to the frequency, we derive that the ratio of the spectrum of the radiated sound power W(f) to the spectrum of the fluctuating hydrodynamic pressure in the jet Spo(f) is W(f)/Spo≃π4(ρc)−1α2D2M4(f/fs), where ρ is the fluid density, c is the speed of sound in the ambient fluid, α is the turbulence intensity, D is the jet nozzle diameter, M is the Mach number, and fs is the Strouhal frequency. The theoretical values of the ratio are compared with data measured with a small turbojet engine...