Thermomechanical analysis of a radial turbine in stationary and transient operation.

The main objective of the present work is to develop an understanding of the stress behavior of turbocharger components by examining the mechanical and thermal loads due to a stationary and transient fluid/solid heat transfer. The approach is to set up a numerical model to define high-stress zones on the turbine wheel and the turbine housing of a turbocharger, then analyze factors that cause these high-stress zones. In this analysis, the previously developed Equalized Timescale Method is used to reduce the computing time of the Conjugated Heat Transfer (CHT) calculation. The result is transferred into realistic heating and cooling times by multiplying with the speedup factor after the computation. The result is then imported into the Finite Element Analysis model (FEA) of the turbocharger components to evaluate the stress fields. The components of interest are a turbine wheel, turbine shaft, and turbine housing. The focus of these investigations shall be the high-stress zones of these parts and the factors that affect them to gain further understanding of the behavior of the stress fields and their effect on mechanical performance. An analysis of the flow field in stationary and transient operations is performed alongside an analysis of the geometry and temperature gradient of the solid body. The result shows that the thermal stress in transient operation mainly depends on initial temperature field development that causes a high temperature-different area. Moreover, locally various flow structures affect the boundary layers at the wall and cause a diverse heat transfer and inhomogeneous temperature fields of the fluid and solid components. These phenomena are analyzed for each zone to find the cause of the high-stress level in those zones. [ABSTRACT FROM AUTHOR]