13th European Conference on Turbomachinery Fluid dynamics & Thermodynamics
In turbomachinery design the accurate determination of thermally induced stresses is of particular importance for life cycle predictions. Due to the increase in exhaust gas temperatures in recent years, thermo-mechanical stresses caused by temperature gradients have an increasingly important role for the life cycle calculations of radial turbines relative to mechanical loads such as centrifugal and vibration forces. An accurate transient thermal finite element analysis (FEA) of turbocharger components requires transient conjugate heat transfer (CHT) analysis. However, due to the vastly different timescales of the heat transfer mechanism in fluid and in solid states, the unsteady CHT simulations are burdened by high computational costs. Hence, for design iterations uncoupled CFD and FEA approaches are needed. The quality of the uncoupled thermal analysis depends on the local heat transfer coefficients (HTC) and reference fluid temperatures (bulk temperatures). In this paper multiple CFD-FEA methods known from literature are implemented into the numerical model of a turbocharger. In order to describe the thermal boundary layer of the fluid, different definitions of bulk temperatures are investigated and optimized with regard to calculation accuracy. For the transient simulation of long heating and cooling processes, the combination of the CFD-FEA methods with two other FEA approaches is examined. Additionally, a structural-mechanical analysis of the cooling and heating processes is conducted. The results of the developed methods are evaluated against experimental data and against the results of the extensive unsteady CHT numerical methods. The methods show a good agreement with this data.