VIBRATION OF PSEUDO-SHOCK IN STRAIGHT DUCT : 1ST REPORT, FLUCTUATION OF STATIC PRESSURE

Abstract

Vibration of a pseudo-shock in a duct often causes noise, vibration and breakdown of the duct. In the present study the wall static pressure fluctuation was measured along the duct and statistically analyzed to make clear the mechanism of the pseudo-shock vibration. The result showed that the vibration had two main frequencies, high and low ones. The former was the natural frequency of the air column in the divergent passage attached downstream of the duct, and the pressure fluctuation propagated in the upstream direction. The latter was the natural frequency of the air column in the duct downstream of the pseudo-shock and this disturbance propagated in the downstream direction. Each vibration was maintained by the interaction of themselves.