Cavitation commonly occurs in fuel injector nozzles, yet the mechanism by which needle valve eccentricity affects in-nozzle string cavitation remains unclear. This study focuses on the development of string-cavitating flow fields and vortex structures influenced by needle valve eccentricity within the nozzle orifice. The Reynolds Stress Model, along with the Volume of Fluid method and the modified Zwart–Gerber–Belamri cavitation model, was employed to evaluate the effects of varying needle valve eccentric distances and orientations on internal flow dynamics. Increasing needle valve eccentricity results in a significantly asymmetric cavitation distribution within the nozzle, enhances vorticity in the main flow region, and strengthens cavitation-vortex interactions, thereby suppressing pressure oscillations. Needle valve eccentricity also significantly alters the intensity and frequency of phase transitions (i.e. fuel vaporization and condensation) within the nozzle orifice. Additionally, needle valve eccentricity promotes vortex instability and increases vortex breakup frequency, while reducing the nozzle flow coefficient by approximately 1–17% compared with the centrally symmetric reference geometry. Needle valve eccentricity fundamentally alters the internal cavitating flow, which can be detrimental to spray uniformity and which is likely to influence subsequent atomization and combustion processes. These findings lay a foundation for optimizing nozzle design to alleviate cavitation-induced flow instability and enhance spray performance.
Tan et al. (Sun,) studied this question.