Numerical Investigation of the Sensitivity of Forced Response Characteristics of Bladed Disks to Mistuning

Abstract

The influence of blade-to-blade coupling and rotation speed on the sensitivity of bladed disks to mistuning is studied. A transonic fan is considered with part span shrouds and without shrouds, respectively, constituting a high and a low blade-to-blade coupling case. For both cases, computations are performed at rest as well as at rotation speeds corresponding to resonant crossings in the Campbell diagram. Mistuning sensitivity is modeled as the dependence of amplitude magnification on the standard deviation of blade stiffnesses. A state of the art finite element reduction technique, based on classical modal analysis, is employed for the structural analysis. This reduced order model is solved for sets of random blade stiffnesses with various standard deviations, i.e. Monte Carlo simulations. In order to reduce the sample size, the statistical data is fitted to a Weibull (type III) parameter model. Three different parameter estimation techniques are applied and compared. The key role of blade-to-blade coupling, as well as the ratio of mistuning to coupling, is demonstrated for the two cases. The mistuning sensitivity behavior of the fan without shrouds is observed to be unaffected by rotation speed at its resonant condition, due to insignificant changes in coupling strength at this speed. The fan with shrouds, on the other hand, shows a significantly different behavior at rest and resonant speed, due to increased coupling under rotation. Comparing the two cases at resonant rotor speeds, the fan without shrouds is less or equally sensitive to mistuning than the fan with shrouds in the entire range of mistuning strengths considered.