Application of the polar correlation technique for source location in subsonic jets

Open Access
Author:
Ha, Su San
Graduate Program:
Aerospace Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
None
Committee Members:
  • Philip John Morris, Thesis Advisor
  • Dennis K Mclaughlin, Thesis Advisor
Keywords:
  • noise source
  • polar correlation technique
Abstract:
A polar correlation technique is used to predict noise source locations in subsonic heated jets. This method enables an estimate of the noise source strength distribution as a function of frequency to be obtained. Far-field microphones, installed on the polar arc of the jet nozzle, record pressure signals which are generated by the jet. Data acquisition is performed for a round nozzle and a beveled nozzle on the long and short lip sides with microphones from 60 degress to 150 degrees to the jet inlet. This data is analyzed to show the effects of the nozzle geometry and the observation angle. The results can be summarized as follows. Irrespective of the shape of nozzle, the significant noise source strength is located within ten nozzle diameters from the jet exit. As the observation angle increases, the highest peak of the noise source strength distribution moves closer to jet exit. However, the noise source distribution shows that the peaks given by the present results are further from the nozzle exit than previously published data. A verification process using an asymmetric Gaussian model explains that this trend is a result of a lack of microphone angular resolution. For the measurement of the polar correlation technique, a graded spacing microphone array is suggested as the quality of the noise source distribution depends on the resolution of the microphones in the array.