On Nonlinear Forced Vibration of Shrouded Turbine Blades

Abstract

Numerical predictions of the forced vibration of a disk assembly including frictional effects between the shrouds are presented concerning engineering needs for the blade design process. Assuming a tuned disk assembly, numerical static, free, and then forced vibration analyses of a shrouded turbine blade measured in the spin pit are performed systematically. For the excitation forces of an air jet evaluated from the fairly linear behavior of the experimental blade resonance peaks, the reliability of the proposed approach is validated through the very close agreement of the computed and measured resonant peaks. These resonant peaks demonstrate either a fairly linear behavior or a nonlinear one like the jump effect of blade resonance amplitudes, or elastic impacts between the shrouds. Also, the damping performance for different contact configurations between the shrouds is numerically analyzed. These numerical results indicate that the shrouds generate higher frictional damping for small angles (0–30deg) between the circumferential direction and the normal vector to the contact surface.

An influence of shroud design parameters on the static stresses of blade assemblies

“…The comparison between the obtained results of the simulations and the data in [2,10] has shown good qualitative agreement (Fig. 6).…”

“…To reduce the vibration level, material or fluid damping are insufficient in most cases, therefore friction damping at different blade joints has to be taken into account. Different friction damping methods can be used to decrease blade vibration, for example, shroud coupling [1][2][3][4], under platform dampers [5,6], or blade-disk joints [1,7]. Moreover, for some tasks, the damping coatings for blade airfoil can be considered [8].…”

“…Considerable attention of researchers has been paid to the study of the influence of the design process as well as operating factors on the stresses of shrouded turbine rotor blades as a pre-requisite of their vibration strength analysis, as evidenced by the investigation results [2,[10][11][12]. Szwedowicz et al [2] present the results of the influence of the contact orientation angle between shrouds on the contact force and contact area as well as free vibration of the blades with different shroud configurations. However, only the beam blade model was considered in this investigation.…”

A New Approach for Solving Rub-Impact Dynamic Characteristics of Shrouded Blades Based on Macroslip Friction Model

“…Xie and Zhang [14] developed a three-dimensional finite element analysis model of shrouded blades based on the macroslip model and the harmonic balance method. Szwedowicz et al [15] analyzed the damping performance for the different contact configurations between the shrouds numerically. Mohammad et al [16] established an analytical expression to compute the Jacobian matrix for 3D friction contact.…”

Fatigue life assessment of a low pressure steam turbine blade during transient resonant conditions using a probabilistic approach

“…The blades experience vibration and resonances at critical speeds [8,11] which produce high dynamic stresses resulting in high cycle fatigue damage accumulation. These dynamic stresses have been shown to be influenced by the source and magnitude of the excitation [9,10] and the damping in the blade [9,11], with approximations of both these variables often required. In the case of a free-standing turbine blade, damping has been shown to be inherently low [12][13][14] which can result in high dynamic stresses at resonance conditions.…”