Formation of Normal Shock in Underexpanded Jet Issuing from Radial Nozzle with Abrupt Expansion

Abstract

A radial underexpanded jet is an underexpanded jet that is discharged by a radial nozzle. In this study, we attempted to control the jet flow by adding abrupt expansion region just downstream of the nozzle exit. Experimental visualization and acoustic measurements were conducted on two types of radial nozzle with nozzle diameter D=12mm and D=16mm, and the relation between the flow field in the abrupt expansion and the noise emitted by the jet was examined. Numerical analysis was also performed for the flow that a normal shock formed in the abrupt expansion region, and the experimental results and the numerical analyses were compared. As a result, the existence of the normal shock was found to be particularly effective in reducing the noise from the jet. In addition, when the jet was exhausted from the small-diameter radial nozzle, the effect of noise reduction is shown to be more pronounced because the wider normal shock is formed.