LAUSR

Abstract The study investigates the critical flow venturi (CVN) with step-wall diffusers for constant volume gas flow rate in critical flow mode. An analytical method for the estimation of the pressure ratio required for the onset of critical flow from these CVN is given. Numerical simulation and experiments have both been employed to compare the onset of critical flow in two types of CVN: ISO 9300 [1] CVN and a CVN with a geometrically similar inlet and a step-wall diffuser with 4 cylindrical sections replacing the conical diffuser. Good agreement between the analytical, numerical and experimental data has been obtained. The CVN with step-wall diffusers have been demonstrated to provide stable flow rate in the critical flow operation mode, however somewhat higher pressure ratio is required to ensure the critical flow in this case.