A Robust CFD Methodology for Physically Realistic and Economically Feasible Results in Racing - Part IV: Intake-Valve Region Flow 2006-01-1591

Part IV of this five-part paper provides an example case study using the recently developed robust CFD methodology and procedures presented in Part I. The first of the four classes of validation cases, documented in Part I, were analyzed here for the flow mechanisms responsible for total pressure losses in the entire intake system, including intake port, valve clearance, combustion chamber, and cylinder regions. Despite having over 5 million finite volumes, all grid meshes showed high quality, as signified by very low maximum and average skewness values of 0.76 and 0.32, respectively. Second order discretization scheme, unusually strict convergence criteria, and carefully enforced “grid independence” for all solutions were employed. To identify the physics of the flow through the intake valve region, four simulations corresponding to high valve lift (HL), medium valve lift (ML), low valve lift (LL) and a case in which the valve was removed, were completed. The flow field results indicate that valve clearance region alone is responsible for more than 50% of the total pressure losses in the entire domain. The computational simulations show that as the flow is accelerated near the convex wall and decelerated along the concave side of the intake port, the resulting unevenly accelerated flow enters the valve clearance region mostly near the convex side. The valve geometry optimization has little or no impact in reducing the total pressure loss in such a non-uniform valve clearance flow situations because only a small portion of the clearance region participates in the flow activity. Results suggest that any optimization attempt should start only after proper intake port curvature is established for uniform clearance flow. In other words, upstream flow conditioning is of critical importance as documented in the present paper. The no-valve case introduced as a supplementary validation showed a counterintuitive feature; an open area may, as documented in this paper, flow less than when it is restricted by a valve.