Estimation of the Nozzle with the Stepped Divergent Section in Critical Flow Regime

A sonic nozzle with a toroidal inlet region, cylindrical throat and a stepped diffuser with cylindrical sections were considered. An analytical method was proposed for estimating the required pressure drop for the nozzle operating in a critical flow regime. The results of analytical estimation of the pressure buildup in the nozzle steps were compared with the ones of numerical simulation. It is shown that replacing the conical divergent section of ISO 9300 standard nozzle with easy-to-manufacture stepped divergent section leads to a twofold increase in the required pressure drop for the nozzle operating in the critical flow regime, which in many cases is acceptable.