Multidimentional simulation of cavitating flows in diesel injectors by a homogeneous mixture modeling approach

Because of intense flow recirculations and strong local depression, cavitation occurs in high-pressure Diesel injectors. Because experiments are very difficult to perform for injection conditions (small length and time scales, high-speed flow, etc.), multidimensional modeling seems to be an appropriate tool in order to better understand the flow features inside and at the exit of the injector nozzle. The purpose of this paper is to present the application of the homogeneous equilibrium modeling (HEM) approach for the simulation of cavitating flows inside a Diesel multihole injector. The validation of the model for typical cavitating flow configurations is presented. The HEM approach allows one to reproduce different cavitation regimes observed experimentally. Indeed, numerical results obtained on a simplified injector [7] agree well with experimental visualizations of cavitation and multiple flow fields. Also, the computed steady-state discharge coefficients of a single hole injector are close to the measured values. Furthermore, numerical results reproduce qualitatively the experimental images of cavitation. Finally, computations of cavitating flows in a six-hole narrow-angle Diesel injector, taking into account the needle displacement, are discussed. It is shown that transient injector exit conditions (i.e., fluid velocity at the injector exit, void fraction, cone angle, etc.) are mainly due to the cavitation collapse especially, during the opening and closing of the injector needle. Therefore, transient computational fluid dynamics code boundary conditions have to be taken into account to improve spray atomization and combustion modeling.