An improved method for coupling the in-nozzle cavitation with Multi-fluid-quasi-VOF model for diesel spray

A hybrid multiphase method is proposed to simulate the cavitation inside the nozzle and the primary breakup of a diesel spray. The improved method coupling the cavitation sub-model with the Multi-fluidquasi-VOF (volume of fluid) model is developed in the OpenFOAM code. In the cavitation sub-model, heterogeneous nucleation of bubble is considered. By reformulating the volume fraction transport equations for liquid and vapor phases in the Multi-fluid-quasi-VOF model, the mass transfer source terms due to cavitation are considered. Moreover, the drag force, virtual mass force and surface tension force of diesel are considered in momentum equation. The computational model is validated by comparing the simulated mass flow rates and the cavitation distributions in an optical nozzle at different inlet pressure against published experimental data. The details of in-nozzle flow and the primary breakup of a diesel spray, such as flow separation, wall shear, cavitation in nozzle and the fragmentation of the jet in spray chamber are captured by applying the proposed method. The area of the evaporation region is smaller than the cavitation area, which leads to the detached tail of the cavitation from the nozzle wall in developing cavitation. The improved method reveals the velocity difference is fairly large at the gas-liquid phase interface and the umbrella shape head bears a great drag force. In addition, plenty of vortexes emerge as the results of the sufficient velocity difference across the interface between air and diesel, which stimulates the Kelvin-Helmholtz instability to promote the initial development of waves on the surface of the diesel column jet and subsequent rapid growth. (C) 2018 Elsevier Ltd. All rights reserved.