Abstract
An radial underexpanded jet is generated in high pressure flow field such as an intake flow through a poppet valve of reciprocating engine, a flow through a main valve of pressure reducing valve and wall jet formed by an impingement of supersonic jet on an object. The radial underexpanded jet resembles an axial underexpanded jet in some ways. Like the axial jet, a cell structure is seen in the radial jet and is visualized as 'shock ring' through which the radial jet flows and spreads. As the radial jet goes downstream, the distance between neighboring shock rings becomes shorter with decrease in thickness of the jet because a cross-sectional area of jet is kept constant. In this study, the structure of the radial free jet without a wall is experimentally analyzed by measuring the sound pressure emitted from the jet and visualizing the flow field from two directions. As a result, a screech tone is measured at high frequency and the frequency decreases as the supply pressure of jet increases. The Strouhal number in two dimensional jet agrees well with Strouhal number estimated using a thickness of 1st or 2nd cell node in the radial jet.
