3D SIMULATION OF TURBULENT AND CAVITATING FLOW FOR THE ANALYSIS OF PRIMARY BREAKUP MECHANISMS IN REALISTIC DIESEL INJECTION PROCESSES

The cavitating in-nozzle flow and primary breakup are investigated for a ballistic injection cycle of a close-to-production 9-hole heavy-duty diesel injector. The Reynolds and Weber numbers correspond to a realistic injection. Real nozzle geometry and a 360° domain are utilized. A pressure-based three-phase volume of fluid flow solver based on OpenFOAM has been developed. A large eddy simulation is performed and primary ligaments split off from the liquid jet core are directly resolved down to the available grid resolution. The interaction of cavitation and turbulence is studied by inspection of vortex structures and a statistical evaluation of primary ligaments. The simulation results are validated by mass flow and laser induced fluorescence (μLIF) measurements of the near-nozzle spray. An agreement to the measured spray shape in the range of the cyclic fluctuations is obtained. A significant asymmetry of the spray shape emphasizes the importance of using the real geometry in the simulation. At low needle lift a multitude of small vortices and cloud cavitation occur in the nozzle hole, while at high needle lift larger string-shaped vortex structures and string cavitation are observed. A comparison with a quasi-steady full lift simulation reveals significant deviations of vortex, cavitation, and ligament structures and thus the highly unsteady flow field generated during the opening phase, which survives far into the closing phase. The highly resolved simulation results contribute to the understanding of the complex physics of in-nozzle flow and primary breakup at realistic diesel injection and may be utilized for enhancements of less resource-demanding primary breakup models.