A numerical procedure to model heat transfer in radial turbines for automotive engines

The thermal condition of a turbocharger considerably differs between different applications, which makes it difficult to model the heat transfer. In this study, a general procedure to characterize the heat transfer model for a radial turbine was established using 3D Conjugate Heat Transfer (CHT) simulation. The external convective and radiation heat losses were modelled by an equivalent convection heat transfer coefficient and an equivalent metal emissivity, following an analysis of the heat transfer mechanisms. The established model was validated by measurements under adiabatic and diabatic conditions. The characterization procedure was further simplified to extend its applications. The number of required operating points for simulation and measurements were significantly reduced, which enabled it to be used under different operating conditions, e.g., engine test and in-vehicle operations, where a constant turbo speed line could hardly be regulated. Then a comparison was conducted with a reference model based on the geometric simplification. The proposed model was observed to give a slightly better result regarding turbine housing temperatures under low and high turbine inlet temperatures. In the end, an analysis of turbine heat flow was conducted, which indicated that on average 80.4% of the turbine internal heat transfer occurred at the volute and 17.3% at the diffuser. Besides, the external heat losses can be up to 2.511 times of the turbine mechanical power.