A Robust CFD Methodology for Physically Realistic and Economically Feasible Results in Racing - Part III: V8 Manifold Flow in Open/Restricted Engines

Part II of this five-part paper focuses on the flow field in the manifold of a V8 racecar engine with the use of the recently developed comprehensive, robust methodology presented in Part I. An exact electronic description of the computational domain for manifold was obtained using the methods described in Part I. Manifold flow was simulated for open and restricted engine configurations and for two unique pair of active runners, including cylinder pairs 1-8 and 3-4. Despite having over 11 million finite volumes, all grids are high quality, with maximum skewness of only 0.74. A second order discretization scheme was used along with unusually strict convergence criteria to obtain fully converged and grid independent solutions in all the cases presented here. The port entrance regions and the dividing walls between the paired runners are primarily responsible for the flow recirculation in the plenum chamber and for the flow separation inside the active runners. This recirculation region was found to extend all the way up to the manifold entrance plane where it creates a low pressure zone. Inactive runners trap the flow that comes from the carburetor, create strong recirculation regions in the plenum chamber and induce severe separation in the active runners. It was found that the inactive runners possess the key design features in reducing the total pressure loss and tuning the ports. The mass flow rate was used as the measure of flow resistance and the overall efficiency of the intake manifold to supply flow to the engine for a given pressure drop are summarized. It is apparent that the manifold in the open engine configuration supplies twice as much air as in the restricted engine configuration.