Efficient CFD Simulations for In-Cylinder Flows Using Hybrid Grids

An edge-based, three dimensional, characteristic-based upwind Roe/TVD unstructured flow solver with chemical kinetics and turbulence modeling for simulation of in-cylinder flowfields, CRUNCH, has been extended to improve computational efficiency and utilize multiple element types. Solution efficiency is achieved using an implicit GMRES time integration procedure which is capable of advancing the solution with very large CFL numbers. The grid motion is accomplished using an automated scheme wherein layers of cells are introduced and subsequently removed as valves increase/decrease lift and as the piston moves through its stroke. A multi-zone mesh framework allows various portions of the domain to slide past each other in a noncontiguous manner. Detailed simulations have been performed for the Ford Motor Company 4.6 liter, twin valve engine. Swirl, tumble, and cross-tumble histories compare well with prior simulations performed at Ford Motor Company. Extension of the current method to a 4 valve engine which exhibits valve-valve “interference” is also addressed. With rapid unstructured mesh generation and limited input setup requirements on the user, the flow solver represents a distinct improvement in available CFD methods for simulating in-cylinder flows.