| The production of bladed structures, e.g. turbine and compressor wheels, is a subject of statistical scatter. The blades are designed to be identical but differ due to small manufacturing tolerances. The manufacturing tolerances may lead to difference in shape, mass and stiffness distribution of the turbine blades. But it can also take effect on inhomogeneities in the material, which are caused by the casting process and can, for example, reflect in residual stresses and grain size differences. These properties can lead to so called mistuning that increases vibration amplitudes compared to the ideal tuned case, which can end in critical vibration conditions. The object of this study is to determine the main source of mistuning for casted turbine wheels in automotive turbocharger applications. The authors have shown in context of a study on mistuning modeling for turbine wheels in automotive turbochargers, that the mistuning due to the geometrical deviation of the shape is not necessarily solely the main mistuning source. To examine this, various numerical models were evaluated, but also measurements during operation and standstill condition were carried out. Casted turbine wheels with different grain structures and also milled turbine wheels from forged round blanks were analyzed. Besides these, FE-models from casting simulations were used to analyze residual stress and material property effects on mistuning. For the milled turbine wheels the source of the mistuning could be assigned to the deviation of the blade shape. The source of mistuning for the casted turbine wheels, however, could be attributed to the material in-homogeneity. |
