Numerical analysis of jet breakup based on a modified compressible two-fluid-LES model

Abstract

Jet breakup with a conical nozzle was studied including in-nozzle flow based on a modified compressible two-fluid model coupled with the large eddy simulation model in the OpenFOAM framework. In order to capture the interface, the phase equation and the pressure equation were modified by adding the quasi-VOF model and surface tension respectively. The effects of temperature and pressure on the air thermal properties were taken into account and the density of diesel was fitted linearly with respect to the pressure according to experimental data. In addition, the Ranz-Marshall model was applied to consider the interphase heat transfer. The modified compressible two-fluid model was verified by comparing the calculated mass flow rates, discharge coefficients, spray momentum fluxes and effective jet velocities under different injection conditions with the available experimental results. It was demonstrated that the numerical simulation results agreed well with the experimental measurements with minor discrepancies which were caused by the numerical assumptions and the experimental uncertainty. Then the mechanism of jet breakup and the effects of the ambient temperature on jet breakup were investigated. It is found that jet breakup is divided into two regions, i.e. the intact region and the jet breakup region. The intact region is dominated by the spatial instability, and the jet breakup region is dominated by the combination of the temporal instability and the spatial instability. It's worth mentioning that the surface tension plays a dual role in inhibiting atomization of droplets and promoting the pinch-off of diesel column and ligament.