Study of an Underexpanded Sonic Jet : 3rd Report, On the Unsteady Characteristics

Abstract

It is industrially important to clarify the unsteady characteristics of an underexpanded sonic jet In this paper, to investigate the instantaneous structure and behavior of an underexpanded sonic jet. issuing from straight circular pipes toward the atmosphere, the visualization of instantaneous flow and measurements of fluctuating pressure with time were carried out over a wide range of mean flow Mach numbers, 0.4∼2. The flow visualization was conducted by booth the spark schlieren and spark shadowgraph methods, and the instantaneous structure of flow was clarified. The fluctuating wave forms of the total and static pressures were measured by a particular microminiature probe with a built-in silicon diaphragm pressure transducer. In particular, the pressures fluctuation with time along the central axis and radial axis of jet flow were investigated. As a result, it was found that the self-excited flow vibration was generated and the characteristics of jet divergence were influenced by the vibration.