The Development of Exhaust Surface Temperature Models for 3D CFD Vehicle Thermal Management Simulations. Part 1 - General Exhaust Configurations

摘要

The thermal prediction of a vehicle under-body environment is of high importance in the design, optimization and management of vehicle power systems. Within the pre-development phase of a vehicle's production process, it is important to understand and determine regions of high thermally induced stress within critical under-body components. Therefore allowing engineers to modify the design or alter component material characteristics before the manufacture of hardware. As the exhaust system is one of the primary heat sources in a vehicle's under-body environment, it is vital to predict the thermal fluctuation of surface temperatures along corresponding exhaust components in order to achieve the correct thermal representation of the overall under-body heat transfer. This paper explores a new method for achieving higher accuracy exhaust surface temperature predictions. To avoid the experimental dependency of fixed exhaust temperature surfaces, a 1-Dimensional fluid stream was integrated within a 3-Dimensional exhaust surface piping network. To encompass the 3-Dimensional effects of combusted internal gas flow, correctional factors were employed. These correctional factors were derived from a study of exhaust gas dynamics and the individual influences on conjugate heat transfer within internal exhaust networks. Four primary phenomenas were found to have significant influence on internal heat transfer coefficients; hence the combination of these effects could be described through a total augmentation factor. Several exhaust configurations were simulated using an in-house heat transfer prediction tool which utilised the work presented in this paper. The results of two particular exhaust configurations are presented within this paper. It was found that both exhaust configurations achieved a good trend in comparison to experimentally derived data. The regions of poor accuracy were found to predominantly exist in components with an internal structure. Over and under predictions of surface temperature were not only dependent on the exhaust model but also on the mass flow rate experienced within the piping network. The source of the error was found to be the multi-layered arrangement assigned to internally structured components within the simulation method of 3-Dimensional surface shells.