Transactions of the Korean Society of Mechanical Engineers B (대한기계학회논문집B)

The Korean Society of Mechanical Engineers (대한기계학회)
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Noise Reduction of an Underexpanded Supersonic Jet via Steady Blowing with Microjets

마이크로 제트를 이용한 과소팽창 음속 제트에서의 소음저감

  • 김진화 (서울대학교 기계항공공학부) ;
  • 김정훈 (서울대학교 기계항공공학부) ;
  • 유정열 (서울대학교 기계항공공학부)
  • Published : 2003.10.01
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Abstract

An attempt to reduce supersonic jet noise is carried out by using two steady microjets in a round jet. The jet is issued from a round sonic nozzle with an exit diameter of 10 mm. Two micro-nozzles with an inside diameter of 1 mm each are installed on the exit plane at an angle of 45 relative to the main jet axis. Far-field noise was measured at 40 diameters off the jet axis. The angle between a microphone and the jet axis is 30 or 90$^{\circ}$. For an injection rate of 4-6% of the main jet, screech tones were completely suppressed by the microjets. The reduction in the overall sound pressure levels were 2.4 and 2.7 dB for 90 and 30 measuring directions, respectively. However, the enhancement of mixing/spreading of the jet by the microjet was negligible. The reduction of noise is probably due to distorted shock cell structures and/or deformed large scale vortical structures by the microjets.

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References

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