Numerical study on the effects of viscous heating and random rough surface on cavitating flow in fuel injection nozzles

Abstract

A transient numerical model was developed to investigate cavitating flow in fuel injection nozzles, incorporating the effects of viscous heating and latent heat of phase change. A three-dimensional Gaussian rough surface generated by Monte Carlo simulation was compared to a wall function correction-based roughness model to assess the impact of surface roughness on both flow and thermal fields. Results demonstrated that viscous heating increased fuel temperature significantly near the nozzle wall, whereas latent heat had minimal effect due to the diesel fuel's low thermal sensitivity. The random rough surface performed better than the wall function correction-based model in inducing local cavitation, reflecting sub-micron scale roughness, and revealing significant randomness in velocity, temperature, and cavitation fields. Roughness height and correlation length were found to be critical factors characterizing surface roughness, where an increase in roughness height and a decrease in correlation length predicted a rougher surface and enhanced effect of viscous heating. The ratio of these two parameters showed a clear linear relationship with temperature rise. Geometric and localized cavitation were observed, leading to temperature increases caused by cavity evolution and collapse. These insights are valuable for improving fuel atomization and combustion efficiency.