Influence of nozzle geometry on the near-field structure of underexpanded sonic jet

Many studies have shown that the Mach disk is one of the most important factors specifying the highly underexpanded sonic jets. However, there has been no acceptable explanation to clarify the dependence of nozzle configuration on the Mach disk. In the present study, a computational fluid dynamics method has been applied to clarify the near field structure of highly underexpanded sonic free jets. Several different nozzles have been employed to investigate the influence of the nozzle configuration on the Mach disk. Based upon the present computational results, a concept of an imaginary straight nozzle was introduced to the orifice flows with a sharp edge. Consequently it was found that the near field structure of highly underexpanded sonic free jets is a unique function of the pressure ratio, regardless of nozzle configuration.