抄録
Recently, reduction of wall heat flux in internal combustion engine has been recognized as one of the key issues to improve thermal efficiency. For maximizing thermal efficiency by suppressing wall heat transfer under the wide range of engine operation, comprehensive understanding and modeling of wall heat transfer are definitely necessary. In general, fully-developed turbulent flow is assumed in existing wall heat transfer models (wall function) used in CFD. However, there are a few studies reported that undeveloped flow was dominated in engine combustion chamber. In undeveloped flow, turbulent Reynolds number that represents the relationship between turbulent production and dissipation is varied in wall boundary layer according to flow condition. This behavior impacts on wall heat transfer. In this study, velocity distribution in wall boundary layer and wall heat flux were measured under engine-like condition with RCEM (Rapid Compression and Expansion Machine). From the experiment, we revealed that it was important for predicting wall heat flux without increasing calculation cost to take into account the difference of spatially averaged turbulent Reynolds number. Considering this finding, the new model was formulated introducing the ratio of turbulent Reynolds number to that in fully-developed turbulent flow. As a result, it was found that our new model was able to predict wall heat flux in internal combustion engine quantitatively with high accuracy.
