Numerical and experimental investigation of unsteady effects in critical Venturi nozzles

A Venturi nozzle, operating mainly at critical conditions, and shaped according to the recommendation of the ISO Standard 9300, was selected for the present study. The flow in the nozzle was investigated numerically for a range of Reynolds numbers and backpressures. The results for one Reynolds number were validated experimentally, making a direct comparison between the numerical and experimental data possible. In the numerical part, the unsteady compressible viscous flow was simulated by Navier–Stokes solver ACHIEVE, developed by the authors. 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 average flow rate and fluctuating discharge coefficient C D.