Investigations on interactions between vortex flow and the induced string cavitation characteristics in real-size diesel tapered-hole nozzles

摘要

An experimental and computational study was carried out to investigate the characteristics of vortex-induced string-type cavitation in the real-size diesel tapered-hole injector nozzle. A transparent-nozzle visualization experiment bench with high-speed imaging technology was applied to capture the string cavitation development in nozzles. Numerical simulations were conducted with the Reynolds stress turbulence model combined with the Schnerr-Sauer cavitation model. The numerical results are in good agreement with the experimental data. Intermittent string cavitation is mainly concentrated in the SAC chamber and near the hole exit due to the complex distribution of vortexes. The recirculated SAC flow encounters upstream injection flow resulting in a large vortex field which induced the formation of string cavitation. A large amount of cavitation vapor entrained by swirling flow is positioned in the near-field spray. Due to the higher dynamic pressure of cavitating flow in this region, the cavitation vapor bubbles are barely changed to liquid phase under the ambient pressure (101325 Pa). Three velocity components: axial, radial and tangential velocity are presented to characterize the flow field of string cavitation. Analysis based on the vorticity transport equation shows that the vortex stretching term is the dominant factor for the formation and development of string cavitation. The effect of dilatation term is secondary, followed by the baroclinic torque term effect on vorticity distribution.