Multiscale Vortex-Induced Breakup and Coordinated Optimization of Nozzle Parameters for Piston Cooling Oil Jets

To address the low oil-droplet impingement capture efficiency and poor cooling performance in marine diesel engine piston cooling jets, a wall modeled large eddy simulation （WMLES） coupled with the volume of fluid （VOF） method, incorporating the S-Omega subgrid-scale model, was employed. Numerical simulations and experiments were conducted to investigate the jet breakup mechanism and nozzle parameter optimization. The results show that the relative error in predicting droplet capture rates is below 5%. The near-field jet breakup is dominated by a multiscale turbulent kinetic energy cascade under axisymmetric mode, where axially extended vortices induce interfacial instability, axisymmetric vortex rings promote film stripping, and small-scale vortices further fragment droplets through energy cascade processes. Based on orthogonal experiments, an optimal nozzle configuration with an aspect ratio of 1.8 and a convergence angle of 30° is identified, increasing the capture efficiency by 5.1%.