Study on the optimal design of mistuned bladed disk (Simultaneous optimization of forced and self-excited vibration and amount of unbalance)

Abstract

Although bladed disks are nominally designed to be cyclically symmetric (tuned system), the vibration characteristics of all blades on a disk are slightly different due to the manufacturing tolerance, deviations in the material properties, and wear during operation. These small variations break the cyclic symmetry and split the eigenvalue pairs. Bladed disks with small variations are referred to as a mistuned system. Many researchers suggest that while mistuning has an undesirable effect on the forced response, it has a beneficial (stabilizing) effect on blade flutter (the self-excited vibration). Therefore, it is necessary to optimize a bladed disk for forced vibration and blade flutter. In this study, a practical optimization method of bladed disks that makes resonant stress and amount of unbalance of the bladed disk minimum by sorting the blades on a disk while keeping the stability for blade flutter. To verify the proposed optimization method, first, the original mistuned bladed disk, which has the maximum amplification factor, is generated by Monte Carlo simulations. Second, the optimal bladed disk with the minimum amplification factor and the minimum amount of unbalance is searched by using Monte Carlo simulations and the genetic algorithm. To keep the stability for blade flutter, alternate mistuning is applied. From the analysis results, the validity of the proposed optimization method is verified.

Keywords

• turbomachinery
• forced vibration
• self-excited vibration
• blade
• flutter
• damping
• mistuning