Unsteady effects in critical nozzles used for flow metering

Abstract A class of critical nozzles, shaped according to the recommendation of the ISO Standard 9300, was selected for the present study. The flow in the nozzles was investigated numerically and experimentally, making a validation of the results by direct comparison possible. In the numerical part, the unsteady compressible viscous flow was simulated by an appropriate Navier–Stokes solver. The experimental work employed flow visualization and accurate pressure measurements to analyze the flow. Significant unsteady phenomena were discovered, leading in some cases to a decrease in the flow rate. The experimental and numerical results were in good qualitative and quantitative agreement.