NUMERICAL ANALYSIS OF THE HEAT TRANSFER IN RADIAL TURBINE WHEELS OF TURBO CHARGERS

摘要

Increasing exhaust gas temperatures of turbocharged Otto and Diesel engines make great demands on the durability of turbine wheels. Hence, a substantiated knowledge about the temperature distribution inside the turbine wheel is crucial. To obtain these temperatures the CHT-method has been applied to a radial turbine of a commercial Diesel turbocharger. The geometry and physical conditions are taken from gas stand tests. Hence, the model includes the entire wheel, the twin scroll housing, and the inlet and outlet pipe. In addition to aerodynamic boundary conditions, thermal boundary conditions have been obtained from gas stand tests. Thermocouples have been applied to blades, hub, back, and shaft close to the piston ring and near to the bearings. The signals have been transmitted via telemetry. A heat transfer investigation clarifies the essential heat transfer mechanisms. The interaction between fluid and solid leads to a non-uniform heat transfer direction, I.e. in some wheel regions heat is even discharged. A discussion about the influence of boundary conditions proves the need to implement not only the turbine wheel solid walls but to include each wall as a solid domain. Since CFD-results are strongly dependent on the boundary conditions, different models are discussed and their influence on the temperature distribution is shown.