Assessment of influences of needle lift and hole height on string cavitation in liquid injection

Abstract

This work uses an improved cavitation model to comprehensively study the impacts of needle lift and hole height on the dynamics of in-nozzle string cavitation. The numerical models can provide a satisfying prediction on internal string cavitation and multiphase vortex flow features in liquid nozzles. Results indicate that the driving mechanism behind the string cavitation inception was the vortex evolution, and the stronger the vortex flow, the stronger the string cavitation. Moreover, the string cavitation patterns were remarkably different under various hole heights due to the evolution characteristics of in-hole longitudinal vortices; specifically, there was an in-nozzle large scale well-organized longitudinal vortices at higher hole heights, while the interaction between the two weaker counter-rotating vortices at lower hole heights resulted in there was no continuous longitudinal vortex inside the nozzles. Furthermore, the quantitative comparison of the inner string cavitation at all of the examined cases under different needle lifts and hole heights shows that appropriately reducing the maximum needle lift of the injector and simultaneously increasing the hole height of nozzles were conducive to inducing the string cavitation on the premise of the large enough flow velocity.