Model of aerodynamics and heat transfer of a turbocharger

Heat transfer has a non-negligible effect on the measurement of turbocharger performance. This leads to an underestimate of the compressor efficiency as well as an overestimate of the turbine efficiency and eventually deteriorates the matching of a turbocharger to an engine. The present work deals with the modeling of aerodynamics and heat transfer of a turbocharger. It aims to quantify the heat transfer of a turbocharger and to improve the 1D simulation by considering the effects of heat transfer. The first part of this work involves a measurement study of a turbocharger on a hot gas test bench under both adiabatic and diabatic conditions. The former is intended to obtain the turbocharger aerodynamic characterizations by minimizing the effects of heat transfer. The latter focuses on investigating the heat transfer behavior under different thermal conditions. During the measurement, the gas quantities and solid temperatures are recorded for validation or to provide boundary conditions for the CFD (Computational Fluid Dynamics) simulation. In the second part, a numerical analysis of heat transfer is carried out by using conjugate heat transfer (CHT) simulation for the turbine and compressor, respectively. With respect to the turbine CHT simulation, a new approach (i.e., combined-CHT) is proposed to improve the resolution of the external convection while maintaining the computational cost. The key idea is to combine the ordinary CHT simulation (i.e., single-CHT) and the complete-CHT simulation, which provides more detailed information on the external convection by modeling the ambient domain. The complete-CHT simulation is observed to give a reliable prediction of the temperature distribution on the turbine housing. As presented in this work, the complete-CHT simulation also allows a quantification of the heat flow of turbocharger. After that, the procedure of a combined-CHT simulation is introduced. Specifically, the complete-CHT is performed only at a single operating point, serving to provide the obtained distribution of external convection coefficient to the single-CHT simulation that is run at the rest of operating points. The combined-CHT simulation is shown to offer reliable modeling of the turbine heat transfer with a computational cost comparable to that of the ordinary single-CHT simulation. This has been verified by the turbocharger test. Nevertheless, further evaluation needs to be made before adoption in other operating scenarios, such as the engine test and in-vehicle operation. As for the compressor CHT simulation, an analysis of the influence of heat transfer on the characterization process is carried out. The measured compressor efficiency is observed to be up to 15 percent lower than its actual value under these conditions. In the third part, a new 1D/3D-FEM (Finite Element Method) model is developed for the turbocharger, combining the 1D model for the flow field and 3D FEM model for the turbine housing and compressor housing. It aims to consider the heat transfer in a 1D simulation, which is usually employed for the engine simulation. The work transfer and heat transfer processes are modeled separately. A general characterization procedure is proposed to determine the external heat transfer parameters. In the end, the 1D/3D-FEM model is compared with the ordinary 1D turbocharger model. The estimated turbo speeds and compressor outlet temperatures from the two models are comparable, while the 1D/3D-FEM model is shown to greatly reduce the error of the estimated turbine outlet temperatures. Furthermore, the 1D/3D-FEM model is expected to be applicable to turbochargers with a variety of configurations in different operating scenarios. Also, the 1D simulation under transient thermal conditions may benefit from the adoption of 1D/3D-FEM model. Nevertheless, the increased computational cost and complexity should be considered.