Numerical investigation of the flow characteristics of underexpanded methane jets

Abstract

In the present work, numerical simulations are carried out to investigate underexpanded methane jets with phase separation effects. In order to predict the fuel injection and the mixture formation in the constant volume chamber, a hybrid, pressure-based solver is combined with a vapor-liquid equilibrium model and a moving mesh methodology. The thermodynamic models are based on the cubic equation of state of Soave, Redlich, and Kwong. A compressibility correction for the widely known kωSST turbulence model is implemented additionally. Application-relevant simulations with a total fuel pressure of 300 bars and five different chamber pressures ranging from 12 to 60 bars were defined. Furthermore, the influence of two fuel and chamber temperatures, 294 and 363 K, is analyzed. Depending on the chamber pressure, two different flow structures of the potential core can be distinguished: (1) A series of typical shock barrels for small pressure ratios and moderately underexpanded jets and (2) a shear layer consisting of a two-phase mixture which enfolds the potential core for high pressure ratios and highly underexpanded jets. Increasing the fuel temperature leads to less significant phase separations, while an increase in the chamber pressure does not affect the structure of the potential core. A comparison with experimental measurements shows a very good agreement of the simulated structure of the potential core, providing evidence that the underlying phenomena are predicted correctly and suggesting that a moving mesh strategy and consistent two-phase thermodynamics implementation are necessary for a physical representation of high-pressure injections.