Jaguar engineers have long wanted to improve the inlet port design process by simulating flow in alternative inlet port designs. CFD, the obvious analysis tool to address this problem, has been used at Jaguar since the late 1980s to model vehicle flows, exhaust catalyst systems, and other design issues. The engineers experienced problems in modeling the complex internal contours of the inlet port and chamber using conventional CFD codes with structured meshing.

In 1996, Jaguar engineers began working with FLUENT, which greatly simplified the modeling of complex flow geometries and made inlet port simulation a very real possibility. One key capability in FLUENT was the ability to create an unstructured tetrahedral grid based on a geometry that is created from scratch or imported by the user from a CAD program. Jaguar engineers typically import geometries from SDRC’s I-DEAS Master Series CAD program into TGrid. They use TGrid to automatically generate a tetrahedral mesh. They then use FLUENT to adaptively refine the mesh so that important flow features are resolved locally while retaining a more cost-effective coarse mesh in regions of smooth flow. Once a surface grid has been generated, the entire process of volume meshing the component takes under 60 minutes.

The basic port geometry and boundary locations of the part to be simulated

The first step in modeling the inlet port and chamber was to validate that FLUENT could accurately simulate the performance of this equipment. Engineers simulated the performance of the AJ-V8 inlet ports using FLUENT on a steady-state rig for two inlet conditions: a medium valve lift and a high valve lift. The predicted data were compared against detailed flow field information, gathered using sophisticated laser techniques. The simulation correlated well with the experimental data. Flow coefficients were predicted within 5% and the tumble ratio between 10% and 40%. Most importantly, comparisons of simulation results for different port designs were consistently accurate in predicting the direction of change in critical output parameters.

Simulation results for the medium valve lift condition

The dramatic improvement in modeling speed combined with the high accuracy of simulation has made it practical to integrate CFD into the inlet port and chamber design process. Jaguar engineers now evaluate concept designs within one week compared to the month or more that was required in the past. In addition, simulation provides far more understanding of the reason why a concept design performs the way it does, making it possible to iterate toward an optimum design more quickly. As a result, engineers have been able to significantly improve the performance of their most recent inlet port designs, increasing flow efficiency by an average of 10% while maintaining turbulence at acceptable levels. These improvements will provide significant reductions in fuel consumption and emissions in future Jaguar engines.

Simulation results for the high valve lift condition

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