Numerical Simulation Of Cavitation Flow And Near-field Spray Of Nozzles Based On VOF Method

Fuel injector nozzle is the terminal part inside fuel injection system of engine, while controlling the fuel flow of injection, the flow condition inside nozzle also bring significant impact on the atomization of fuel jet, which is directly related to the combustion and emissions of engines. It has been pointed out through a number of studies that the cavitation process takes place in the nozzle has an important influence on the internal flow and the external jet atomization. Therefore, it’s very necessary to carry on research of the complete injection process including the internal flow and the external jet formation spray, in considering the cavitation process inside nozzle. In view of the difficulty of observe the change of flow field inside nozzle under experimental condition, it is obvious that numerical simulations are very promising to study and analysis the jet flow around the injector nozzle.The research based on the method of VOF (Volume of Fluids), on the basis of establishment of multiphase model for three phase flow(liquid, vapor, and gas), with the addition of cavitation model, transform the mass conservation equation and volume fraction equation of multiphase flow, establish the numerical model for cavitating multiphase flow.Refer to those source code of related strandard solvers inside OpenFOAM. which is an open source software in computational fluid dynamics field operated under Linux system, the solver named interMpcFoam is self-designed and compiled to solve the cavitating multiphase flow issue, and thus established the CFD computing platform for simulating the nozzle injection process including the cavitation process and the jet atomization process. The newly developed solver called interMpcFoam, involves the flow process of multiphase flow, the cavitation of phase change process between liquid and vapor, and the mutual diffusion process between air and vapor. The solver allows the user to choose the corresponding cavitation model when running simulation cases, and select the related turbulent model that supported in OpenFOAM if necessary. With the reference to the relevant paper about the experiment of cavitation process in the jet flow, we carry out a series of2-dimension simulation aim at the cavitation occurs inside nozzles at different condition, the simulation results are compared with the experimental results. The results show a good agreement, thus testify the authenticity of both the numerical model and the solver compiled in OpenFOAM, also reflect relevant laws of the cavitation consistent with the conclusions of experiment. Not only did the simulation results of2-dimensional nozzle prove the feasibility of this research method for studying cavitation process and jet atomization, but also provide the relevant experience of setting model and control parameters for the actual nozzle injection process simulation.On the basis of works in2-dimensional nozzle injection cavitation flow, carry out a3-dimensional simulation focus on the high pressure diesel injection, including cavitaion process and jet atomization, of an actual VCO nozzle. The simulation results show internal cavitating flow and external jet atomization of the fuel injection through nozzle, the verify the influence on jet formation and atomization from caviation process. According to those images of fuel injection process and the flow field situation, comparing with the injection atomization result of no cavitation model simulation, thus analysis influence on the external jet spray process from the asymmetric structure of nozzle which result in asymmetric cavitation process. Through the in depth analysis of spray atomization condition, made a further confirmed the two stage of fluid jet atomization process, that is the initial atomization caused by the internal cavitation process and turbulence effect, secondary atomization describes in the air-assisted atomization theory.