Improved Engine Wall Models for Large Eddy Simulation (LES)

Improved wall models for LES are presented in this paper. The classical Werner-Wengle (WW) wall shear stress model was used along with the eddy viscosity near walls. A sub-grid scale turbulent kinetic energy was employed in a model for the eddy viscosity. To provide heat flux results, a modified classical variable-density wall heat transfer model, which includes the variation of the turbulent Prandtl number in the boundary layer, was also employed. The fully turbulent developed flow in a square duct with constant wall temperature was used to validate the model and the friction factor and Nusselt number predictions are in good agreement with experimental results. The resulting time and spatially averaged velocity and temperature wall functions from the new wall models match well with the law-of-the-wall experimental data. Additionally, the model was validated using experimental data from a Caterpillar engine operated with conventional diesel combustion. The computational pressure and heat release are well predicted when comparing with the experimental measurements. There is successful matching between the predicted wall heat fluxes and measurements taken at ten points on the piston surface. Compared with the previous RANS-based wall models, the new models generate more accurate predictions, which agree better with experimental data.