The focus of the paper is the analysis of mistuning, that is small deviations of the blade properties e.g. due to manufacturing tolerances. The resonant amplitudes of turbine blades are very sensitive to these deviations which can lead to significantly increased vibratory response of some blades with increased risk of high cycle fatigue.
The main part of the paper discusses methods that can be used to find blade patterns which are insensitive to energy localization. The sensitivity of the forced response against harmonic mistuning, that is a harmonic alignment of the blades respective to the mistuning factors of the single blades, is examined. A previously developed reduced order model is used to efficiently conduct Monte Carlo Simulations (MCS). Especially the influence of the variance of the harmonically mistuned blade patterns is discussed. On the basis of this analysis rules are developed to suppress the energy localization. The rules are mainly focused on the alignment of the blades around the bladed disk. The approach also takes advantage of the special properties of harmonic mistuning patterns. An assignment of the blades to insensitive harmonic mistuning patterns with a specific variance and number of periods is used to reduce the maximum of the amplification factor of the forced response. A similar approach uses intentional mistuning patterns with different blade types which are aligned harmonically and are insensitive to an additional stochastic mistuning. In case of specific combinations of the dependent parameters, especially the variance of the mistuning factors and the number of periods, the energy localization can be reduced considerably.