A numerical study on the in-nozzle cavitating flow and near-field jet breakup of a spirally grooved hole nozzle using a LES-VOF method

Abstract

• The multiphase flow over a spirally grooved hole nozzle was numerically investigated. • The spirally grooved hole led to partially spiral velocity field at the hole outlet. • The centrifugal force caused by spiral grooves promoted the breakup of liquid jets. • The spirally grooved hole nozzle yielded wider spreading angle and finer droplets. To enhance fuel atomization for diesel engines, a spirally grooved hole (SGH) nozzle, in which several spiral arc grooves are set on the inner wall of tapered holes of a nozzle, forming flower-shaped cross sections, was designed. In this paper, the multi-phase flow inside and outside the SGH nozzle was calculated using a volume-of-fluid, large eddy simulation (VOF-LES) method to clarify the effects of spirally grooved hole on the cavitating flow and primary breakup characteristics for diesel nozzles. The calculation was carried out under injection pressure of 150 MPa and ambient pressure of 0.1 MPa for a SGH nozzle, and a non-grooved tapered hole (NSH) nozzle as a reference. Numerical results showed that the wall-guide effect of the spiral grooves in the hole of the SGH nozzle led to partially spiral flow of the fluid at the outer part of the nozzle hole, which in turn produced considerable centrifugal force on the liquid core, providing additional dynamics for the breakup of liquid jets besides aerodynamic effects. As a result, the deformation of the surface of the liquid column in a shorter distance from the outlet of the SGH nozzle were observed, and more ligaments and droplets were formed in the near-field, i.e., the breakup of the jet emerging from the SGH nozzle was substantially enhanced. The partially spiral flow also resulted in a largely wider near-field spreading angle and finer droplets than those of the NSH nozzle, with a penalty of 11.8% lower discharge coefficient.