Numerical Investigation and Experimental Comparison of the Gas Dynamics in a Highly Underexpanded Confined Real Gas Jet

Abstract

A numerical study for a supersonic underexpanded argon gas jet driven by a pressure ratio of 120 is described in this work, and the results are compared to experiments. A single phase large-eddy simulation (LES) employing a fully-coupled pressure-based finite volume solver framework is carried out. The numerical results are validated against experimental Schlieren and particle-image-velocimetry (PIV) measurements taken under the same conditions. Due to the high pressure conditions imposed on the gas, real gas effects are taken into account via the Peng-Robinson equation of state. This approach enables the accurate prediction of the gas properties throughout all pressure conditions encountered within this study. Flow velocity data obtained from numerical simulations and experiments are presented, leading to valuable insights into the features of the flow. Comparisons between experimental and numerical Schlieren images show a very good agreement for the location and shape of the main shock structure in the near nozzle exit region. The predicted velocity field further downstream, at a stream-wise distance over 100 nozzle diameters from the nozzle exit, is reasonably close to the PIV data, with less than 25% difference between the root-mean-square (RMS) simulated and experimental velocity field. The agreement obtained in this study is remarkable in light of the challenging flow configuration involving a vast range of flow speeds and time scales. There are also discrepancies, predominantly for the near-throat velocity profiles obtained from PIV measurements and numerical simulations: in the immediate post-shock region the simulation results predict a major converging throat of low, subsonic fluid velocity surrounded by the supersonic shear layer, which is not observed in the experiment.