Effects of aeroelastic phenomena on the vibration localization in mistuned bladed disks.

Mistuning, small differences among sectors of bladed disks, is unavoidable because of manufacturing tolerances and in-service wear and tear. Mistuning can be very dangerous because it might cause energy localization and early failure of certain blades. Finite element analysis is computational formidable for mistuned bladed disks because the loss of cyclic symmetry requires analysis of the full sector model and mistuning can be totally random. Hence, a great amount of research effort have been devoted to develop efficient and accurate reduced-order structural models. Real bladed disks are usually operated in high pressure and high temperature air flows. Although linearized frequency domain aerodynamic models have been developed in recent years, utilizations of these aerodynamic models with high fidelity structural models of mistuned bladed disks are limited. A new iterative aeroelastic coupling procedure is developed in this dissertation. A group of tuned system modes are used to calculate unsteady aerodynamic modes. Vibration eigenvalues and mode shapes are obtained by iterative computation. It is shown that free and forced aeroelastic responses of mistuned bladed disks can be significantly different from structural-only responses. Also, blade-disk interface constraint modes are needed if cantilevered-blade normal modes are used to calculate unsteady aerodynamic forces. The aerodynamic model has been extended from subsonic regime to transonic regime by employing the upwinding technique. Parametric studies show that inflow incidence angle and Mach number can relieve the severity of mode localization. Also, inflow Mach number changes the sensitivity of mistuned forced response to mistuning levels. In this dissertation, a new hybrid technique is also developed to predict the iteration steps needed to obtained converged results. It is of great importance because the iterative aeroelastic calculation consumes a great amount of computation time. Several critical ratios are proposed to characterize the aeroelastic system. The predicted results are validated with actual aeroelastic computation results, and Monte Carlo simulations are conducted to study effects of important factors on the convergence history. It is found that among these critical ratios, the aerodynamic ratio and the aerodynamic gradient ratio are the two most important factors.Ph.D.Applied SciencesMechanical engineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/126712/2/3276179.pd