Numerical study on the influence of convergent–divergent nozzle structures on the in-nozzle flow and jet breakup based on the OpenFOAM 2020-01-1156
The non-conventional diesel nozzles have attracted more and more attentions for their ability to promote jet breakup. In the present study, the internal nozzle flow and jet breakup relying on the convergent–divergent nozzle are investigated by combining the cavitation model and LES model with Multi-Fluid-Quasi-VOF model based on the OpenFOAM code. The novelty of this method is that the interphase forces caused by the relative velocity of gas and liquid could be taken into account while sharpening the gas-liquid interface, which can accurately present the evolution processes of cavitation and jet breakup. Primarily, the numerical model is verified by the mass flow rate, spray momentum flux, discharge coefficient and effective jet velocity of the prototype Spray D nozzle from R. Payri et al. Then keeping the inlet and outlet diameters of spray D nozzle as constant, the diameters at 1/4, 1/2 and 3/4 of axis distance from the inlet of the spray D nozzle are changed to 160 μm respectively to obtain three different convergent–divergent level nozzles. The transient internal nozzle flow and jet breakup of the three different convergent–divergent level nozzles are presented and their characteristics are analyzed. The results demonstrate that cavitation is formed downstream the throat of the convergent–divergent nozzles and the formation of supercavitation is accelerated by the high convergence–divergence level. In addition to the strong disturbance caused by cavitation, the divergence in the final part of the nozzle results in a larger radial jet velocity, which brings about that the liquid column breakup angle is greatly increased by the higher convergence–divergence level.
Weilong Zhang, Canxu Liu, Bo Zhang, Hong Liu, Ming Jia, Yanan Yan