Nonlinear Vibration Analysis of Turbine Bladed Disks with Mid-Span Dampers

Friction dampers are one of the most common secondary structures utilized to alleviate excessive vibration amplitudes in turbo-machinery applications. In this paper, the dynamic behavior of the turbine bladed disks coupled with one of the special damper designs, the so-called Mid-Span Dampers (MSDs) that is commonly used in steam turbines of Baker Hughes Company, is thoroughly studied. Friction between the blade and the damper is modeled through a large number of contact nodes by using 2D contact elements with a variable normal load. In the solution procedure, the coupled static/dynamic Harmonic Balance approach is utilized for the first time in the assessment of the dissipation capability of MSDs, computationally shown by predicting the forced response levels of the system at different resonances. Moreover, it is demonstrated that the nonlinear dynamic response is non-unique and it may vary considerably even if all the user-controlled inputs are kept identical. This phenomenon is a novel observation for MSDs and it is explained by an uncertainty present in the contact forces. Contact conditions corresponding to multiple responses are also investigated to unveil the different kinematics of the damper under the same nominal conditions.

Modeling and analysis of a mistuned fan blisk

Turbomachinery has a vital role in the industrial engineering and the bladed disks such as; compressor, impeller pumps, turbine generator and jet engines are the critical components of turbomachinery. This work is focused on the “mistuning effect” of bladed disks of a turbine, which creates the lack of symmetry and ultimately damages the turbine blade. In order to completely understand the severity of the damage caused by the mistuning effect on the turbine disk, the study and analysis of the model parameters is very important. This work provides an insight to the various effects caused by the presence of crack and mistuning levels, in the mistuned turbine blisk, by using smeared material properties and modal assurance criterion (MAC) techniques. Moreover, a mistuned blisk model with four cracks (at various locations and different depth levels) has been developed and compared with the tuned blisk model, in order to determine the severity of damage occurred. The MAC results indicate that the severity of damage may vary depending on the location and depth of the crack and mistuning may alter the dynamic and vibrational characteristics of the structure.

Accurate Interpolation of the Dependency of Modal Properties On the Rotation Speed for the Transient Response Analysis of Bladed Disks

During fast gas-turbine engine acceleration and deceleration the transient vibration effects in bladed disk vibration become significant and the transient response has to be calculated. In this paper an effective method is developed for efficient calculations of the transient vibration response for mistuned bladed disks under varying rotation speeds. The method uses the large-scale finite element modelling of the bladed disks allowing the accurate description of the dynamic properties of the mistuned bladed disks. The effects of the varying rotation speed on the natural frequencies and mode shapes of a mistuned bladed disk and its effects on the amplitude and the spectral composition of the loading are considered. The dependency of the modal characteristics on the rotation speed are based on the evaluation of these characteristics at reference points followed by the interpolation to obtain values at any rotation speed from the operating range. A new method has been developed for the interpolation of mode shapes while preserving the orthogonality and mass-normalization of the mode shapes. The method of mode shape interpolation is elaborated for tuned and mistuned bladed disks. The accuracy and efficiency of the method is demonstrated on test examples and on analysis of transient forced response of realistic bladed discs.