Experimental and Numerical Investigation of Heat Transfer in a Turbocharger Turbine in Consideration of a Diabatic Heat Shield

Thermal loads play a major role in determining a turbocharger turbine’s lifecycle. The turbine wheel in particular is subject to varying thermal loads, which induce inhomogeneous temperature distributions causing thermo-mechanical stress. In order to calculate these thermal loads the mechanisms governing the heat transfer inside a turbocharger turbine have to be known as precisely as possible. One of these mechanisms is heat transfer from the wheel backside through the heat shield into the bearing housing, which is commonly neglected. This paper aims to fill that gap by exploring the effect of heat transfer through the heat shield of a turbocharger using both experimental and numerical data. As part of this investigation a brief summary of the experiments with an instrumented turbocharger is presented. These experiments subjected the turbine to several stationary load conditions ranging from minimum to maximum operating points for multiple rotational speeds. Hereby, temperatures in the stationary and rotating parts of the turbine were recorded. Due to the complexity of the temperature field inside the turbine, experimental data alone does not offer a sufficiently detailed account of the occurring processes, because it is only recorded at discrete points. Therefore, a numerical model is presented, which encompasses both fluid and solid parts of the turbine to enable CHT simulations to be conducted. These simulations allow for a more complete analysis of the heat transfer between turbine wheel and bearing housing due to the availability of data at all locations. To verify the correctness of the numerical results the model is first validated using the experimental data and shown to be a good match. It is then used to analyze heat transfer mechanisms between the backside of the turbine wheel, heat shield and bearing housing, as well as their impact on the temperature field of the turbine wheel.