A Robust CFD Methodology for Physically Realistic and Economically Feasible Results in Racing - Part V: Exhaust-Valve Region Flow 2006-01-1592

Part V of this five-part paper investigates the flow field and the total pressure loss mechanisms for three valve lifts in the exhaust region of a V8 racecar engine using the robust, systematic computational methodology described in Part I. The replica of the engine geometry includes a cylinder, detailed combustion chamber, exhaust valve, valve seat, port, and “exhaust pipe”. A set of fully-converged and grid-independent solutions for the steady, time-averaged (or RANS), non-linear Navier-Stokes equations are obtained using dense and high quality grids, involving 2.1∼3.0 finite volumes, and unusually strict convergence criteria. Turbulence closure is attained via the realizable k-ε (RKE) model used in conjunction with the non-equilibrium wall function near-wall treatment. The validation presented in Part I showed that flow rate results from the “blind simulations” agree well with the experimental measurements. The relative magnitude of total pressure losses in the entire exhaust valve flow region and the physics mechanisms responsible for the outcomes are presented and compared among three cases involving low (LL), medium (ML) and high (HL) valve lifts. Detailed descriptions are provided for the location of loss regions, mechanisms responsible for these losses, and the relative magnitude of different loss sources. Solutions for all three valve lift cases indicate that increasing valve lift results in a decrease in both the total pressure loss in the entire region and the net total pressure losses within the valve clearance region. The ML and HL case results show that the exhaust valve clearance itself is the maximum total pressure loss sub-region. However, it is the port sub-region that is responsible for the highest loss level in the LL case. These observations are contrary to the intake valve study presented in Part II. The most unique flow feature for the low valve lift case turns out to be in the port sub-region, where losses are maximized. Finally, the present results show strongly coupled flow in various sub-regions leading to the observation that experimental or computational studies conducted on isolated exhaust valve clearance regions cannot capture the essential physics.