An experiment on the noise source strengths in coaxial double jet.

Abstract

The distribution of noise source strengths in a coaxial double jet with main nozzle diameter 12mm and nozzle exit area ratio 2. 83of bypass flow to main flow is measured by the use of a reflector-type directional microphone system. Sound pressure spectrum in the far-field which is predicted with the sound source distribution is in well agreement with the measurement by an omnidirectional microphone at each velocity ratio of the bypass jet to the core jet. Therefore, a reflector type directional microphone system is considered to be suited for the measurement of sound source distribution in the coaxial double jet. Next, the author measures the pressure fluctuation in an incompressible jet flow with the use of a probe microphone with four static pressure holes and obtains the influence of correlation upon the far-field noise at each Strouhal number on the basis of the distribution of noise source strength and local pressure fluctuation. Moreover, the reason of the noise increase or decrease of the double jet to the single jet is considered.