Numerical Simulation Internal Flow Field And Cavitation Phenomena In A Nozzle

The internal flow and cavitation phenomena in a nozzle hole are thought to be a very important factor to affect fuel inject and atomization performance, thus directly influence dynamical and emission performance of diesel engines. The study of the internal flow inside the nozzle of the fuel injector is limited by several factors, including the extremely small size and detailed structures of the nozzle and complex flow. Experimental study is very difficultly for flow characteristic inside.For this reason, this paper studies the internal flow and cavitation phenomena by numerical simulations with commercial CFD software---ANSYS FLUENT, and does research into parameters of the nozzle initial conditions and geometry. The results can be applied to provide theory basis for injector improvement. Works completed in this paper are mainly as follows:1) The changing regularity of contour of pressure and velocity inside the nozzle under different needle lift are obtained by three-dimensional numerical simulation. Effects on flow field of the differences of injection pressure, nozzle diameter, inlet corner radius and nozzle inwall roughness are obtained through simulated result. 2) The nozzle structure is restructured based on two existed nozzle structures---STD and VCO, and then the odds are obtained among the three structures through simulation.3) The cavitation phenomena in a two-dimensional nozzle is numerically simulated. Effects on cavitation of the differences of pressure between the inlet and outlet, the ratio of length to diameter, and the ratio of the inlet corner radius to diameter are discussed.4) The developing process of cavitation in converging and diverging nozzles is numerically studied. The effect on cavitation of converging and diverging coefficient is analyzed in detail.