Measurement on acoustic source-strength distribution of coaxial jets

The distribution of acoustic source strength in coaxial jets has been studied experimentally by the reflector-mirror microphone method. The acoustic sources are most intensively distributed in the mixing regions between the inner and outer jets. The source strength in this region is greatly dominated by the relative velocity of the inner and outer jets, taking the minimum at the velocity ratio of about 0.5. The area ratio and the relative position of the nozzles are changed to study their effects on the source distribution. Increase in the area ratio shifts the acoustic source downstream in the outer jet without any change in the inner jet. Extending the inner jet nozzle moves the noise source in the inner jet to the downstream without any change of the outer jet, while extending the outer nozzle shifts wholly the noise source distribution downstream.