Modeling and analysis of a mistuned fan blisk

Abstract

Turbomachinery has a vital role in industrial engineering and is used for transfer of energy. Bladed disks such as compressor, impeller pumps, turbine generator and jet engines are the critical components of turbomachinery. In this research we have focused on bladed disks of the turbine. It deals mistuning effect on the disks that creates lack of symmetry in the turbine blade. Due to lack of symmetry in extreme operation, turbine blades may cause an increased force response due to fatigue and may result in unexpected failure. This effect on the turbine disk may happen due to certain material properties and manufacturing restraints. In order to understand the actual meaning of mistuning effect on the turbine disk, the study of model parameters of turbo machinery blade is very important. These parameters are very sensitive to these mistuning patterns that are inherent in the structure. Moreover, cracks formation besides mistuning is another factor that effects the turbine disk. This causes stiffness loss at crack location; stiffness loss alters the dynamics of the structure. This paper gives an insight to determine the effects of presence of crack and mistuning levels in mistuned turbine blade by using smeared material properties and modal assurance criterion (MAC) techniques. Mistuning at mistuned zone causes a split in vibration modes that are represented by gradual increase of ‘E’ (Modulus of Elasticity) value of certain elements in finite element analysis (FEA). A comprehensive way of finding complex mistuned patterns in repeating structures has been practiced in this work. Furthermore, the characteristics of mistuned blisk model having cracks of various patterns regarding its depth and location are compared with the tuned blisk model to determine the severity of damage occurred. For investigation purposes, the crack model mode shapes are obtained by penetrating the cracks at four different locations one after the other successively. The change in mode shapes and MAC results indicates the severity of damage with the crack depth ratio at certain location. A numerical value of damage is obtained by subtracting MAC matrices of crack damaged model from MAC metrics of reference model.