A study on formation process of plate shock in underexpanded impinging jet

Abstract

This study focuses on the formation process of plate shock in an underexpanded jet impinging on a flat plate. The jet discharged from a convergent nozzle is underexpanded when the pressure ratio across the nozzle exceeds the critical value. When the jet impinges on a flat plate perpendicularly, a shock wave called ‘plate shock’ is formed in the jet. In such flow filed the impinging jet violently oscillates, which leads to a complicated flow field with a noise of high sound pressure level. In application of the jet to industrial use, careful attention should be paid to the behavior of jet with noise emission, in particular, the behavior of the plate shock. In this study, the nozzle-plate distance was changed, and the flow field was experimentally observed with attention to the formation of plate shock. Shadowgraph method was used to visualize the flow field and a structure of the jet was examined. As a result two weak shocks were observed upstream of the flat plate and these were found to play an important role in formation and disappearance on the plate shock.