Effects of Nozzle Contour on the Aerodynamic Characteristics of Underexpanded Annular Impinging Jets

Abstract

Dependence of the flow behavior of underexpanded annular impinging jets on the nozzle contours is investigated experimentally. In the present study, five converging annular nozzles of different contours are fabricated and tested. The most important parameters of the annular nozzle contour are the ratio of the inner diameter d to the outer diameter D and the angle α of the ejection. The flow visualization using the shadowgraph method and the pressure measurements at the impinged surface show that the shock structure in the jets and the surface pressure strongly depend on the nozzle contour. It is demonstrated that the impinging jet issuing from an annular nozzle with large d/D and large α produces high surface pressure concentrated at the jet center. These results suggest that annular nozzles show great potential for assisting laser cutting.