A NUMERICAL SIMULATION OF UNSTEADY AXISYMMETRIC TURBULENT FLOW IN A RECIPROCATING ENGINE INCLUDING PORT/VALVE ASSEMBLY

A numerical simulation of unsteady axisymmetric turbulent flow was performed for a reciprocating engine including port/valve assembly.
The governing equations based on a non-orthogonal coordinate formulation with Cartesian velocity components were used and discretised by the finite volume method with non-staggered variable arrangements. The modified k−ε turbulence model which included the effect of compressibility was used. The results of two-dimensional transient calculation for the axisymmetric configuration were compared with the experimental data[l]. Although slightly low rms velocity was predicted compared to the experimental data, the predicted velocity distributions at the valve exit and in-cylinder region showed good agreements with the experimental data. The flow at the valve exit was separated at the same valve lift position with the experimental data. The mean flow pattern at the valve exit was found to be more sensitive to valve lift than mass flow rate or valve motion. Two vortices in-cylinder region were generated during the initial intake process. The clockwise main vortex became strong and moved upward to the top wall. The counter-clockwise second vortex became weak and stick to the upper left corner of the cylinder. After middle intake process, new vortex adjacent to upper cylinder wall appeared by the piston motion and therefore, the in-cylinder flow was formed into three vortices. The cylinder pressure just before bottom dead center of piston was higher than inlet pressure and then the reverse flow occured at the valve exit. The in-cylinder flow characteristics were strongly dependent on piston motion, but insensitive to valve motion.