Multidimensional port-and-cylinder flow calculations for two- and four-valve-per-cylinder engines: Influence of intake configuration on flow structure

Results of three-dimensional coupled intake port and in-cylinder flow calculations, including moving valves, are reported. These computations have been performed using a recently developed unstructured-mesh flow code; moving valves are accommodated via a new algorithm for arbitrary three-dimensional mesh deformation in response to moving boundaries. The geometry is intended to simulate a generic four-valve head with two intake ports. Computations are started at intake valve opening and are carried through top-dead-center of compression. A standard k - Ïμ model is used to represent turbulent transport of momentum. Of principal interest is the evolution of and interaction between the large-scale induction-generated mean flow structure and turbulence. In particular, we seek to understand the role of swirl and tumble in generating near top-dead-center turbulence. Global balances of in-cylinder mean angular momentum, mean kinetic energy, and turbulence kinetic energy are the principal diagnostics used to investigate these aspects of the flow. Results for four configurations are presented: 1) single intake valve; 2) dual intake valves; 3) dual intake valves with swirl shrouds; and 4) dual intake valves with tumble shrouds. Comparisons among the angular momentum and energy budgets for these four cases, and especially the latter two, serve to elucidate the different mechanisms by which angular momentum evolves and by which energy is exchanged between mean flow and turbulence in the engine cylinder. Limited comparisons with measurements are reported. Salient conclusions of this work are: first, that multidimensional coupled port-and-cylinder calculations are feasible and yield results of sufficient accuracy to resolve differences in post-intake-valve-closure flow fields induced by different intake configurations; and second, that (for this geometry) a tumbling flow is more effective than a swirling flow at extracting energy from the piston motion during compression and at converting this mean flow energy into turbulence. Many other interesting differences between swirl and tumble are discussed.