Vibration Modes of Packeted Bladed Disks

1984 ◽  
Vol 106 (2) ◽  
pp. 175-180 ◽  
Author(s):  
D. J. Ewins ◽  
M. Imregun
Keyword(s):  
Natural Frequencies ◽  
Turbine Blades ◽  
Vibration Modes ◽  
Nodal Diameter ◽  
Vibrational Behavior ◽  
Bladed Disk ◽  
Methods Of Analysis ◽  
Receptance Coupling ◽  
Modal Interference ◽  
Series Of Experiments

This paper presents the results of investigating the vibrational behavior of turbine blades when grouped into packets. Two methods of analysis based on substructuring via receptance coupling have been developed and used with success to predict the natural frequencies of a 30-bladed disk with various packeting arrangements. A series of experiments have been conducted on a special testpiece to confirm these predictions. It is found that, unlike its continuously shrouded counterpart, the packeted bladed disk has modes which are always complex in shape, containing several nodal diameter components, a feature which can be predicted from the modal interference diagrams introduced in this work.

scholarly journals Vibration analysis of rotating rings with complex support stiffnesses

2018 ◽  
Vol 237 ◽  
pp. 01010
Author(s):  
Fuchun Yang ◽  
Yue Zhang ◽  
Hailong Li
Keyword(s):  
Differential Operators ◽  
Natural Frequencies ◽  
Frequency Separation ◽  
Vibration Modes ◽  
Governing Equations ◽  
Nodal Diameter ◽  
Vibration Properties ◽  
Matrix Differential Operators ◽  
Matrix Differential ◽  
Space Matrix

Vibration characteristics of rotating rings with complex support stiffnesses are studied. The complex stiffnesses of the rotating ring include discrete stiffnesses and partially distributed stiffnesses. The governing equations are established by Hamilton’s principle. The governing equations are cast in matrix differential operators and discretized using Galerkin’s method. The eigenvalue problem is dealt with state space matrix and the natural frequencies and vibration modes are obtained. The properties of natural frequencies and vibration modes of rotating rings are studied. The results illustrate that frequency separation and frequency veering happen with the increase of rotation speed. The vibration modes are not dominated by only one nodal diameter while dominated by several nodal diameters because the discrete and partially distributed stiffnesses disrupt the axisymmetry of rotating rings. The influences of several parameters to vibration properties of rotating rings are also investigated.

Numerical Investigations of Localized Vibrations of Mistuned Blade Integrated Disks (Blisks)

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
T. Klauke ◽  
A. Kühhorn ◽  
B. Beirow ◽  
M. Golze
Keyword(s):  
Strain Energy ◽  
Vibration Modes ◽  
Blade Vibration ◽  
Nodal Diameter ◽  
Mode Localization ◽  
Bladed Disk ◽  
High Pressure Compressor ◽  
Localized Vibrations ◽  
Pressure Compressor ◽  
Higher Sensitivity

Blade-to-blade variations of bladed disk assemblies result in local zoning of vibration modes as well as amplitude magnifications, which primarily reduces the high cycle fatigue life of aeroengines. Criteria were introduced to determine the level of these mode localization effects depending on various parameters of a real high pressure compressor blisk rotor. The investigations show that blade vibration modes with lower interblade coupling, e.g., torsion modes or modes with high numbers of nodal diameter lines, have a significantly higher sensitivity to blade mistuning, which can be characterized by the higher percentage of blades on the total blisk strain energy.

Approach to Unidirectional Coupled CFD–FEM Analysis of Axial Turbocharger Turbine Blades

2001 ◽  
Vol 124 (1) ◽  
pp. 125-131 ◽  
Author(s):  
D. Filsinger ◽  
J. Szwedowicz ◽  
O. Scha¨fer
Keyword(s):  
Turbine Blades ◽  
Fem Analysis ◽  
Turbine Stage ◽  
Time Resolved ◽  
Nodal Diameter ◽  
Numerical Investigations ◽  
Bladed Disk ◽  
Steady State Responses ◽  
Bladed Rotor ◽  
State Responses

This paper describes an approach to unidirectional coupled CFD–FEM analysis developed at ABB Turbo Systems Ltd. Results of numerical investigations concerning the vibration behavior of an axial turbocharger turbine are presented. To predict the excitation forces acting on the rotating blades, the time-resolved two-dimensional coupled stator–rotor flow field of the turbine stage was calculated. The unsteady pressure, imposed on the airfoil contour, leads to circumferentially nonuniform and pulsating excitation forces acting on the rotating bladed disk. A harmonic transformation of the excitation forces into the rotating coordinate system of a single blade was elaborated and the complex Fourier amplitudes were determined. The bladed rotor was modeled by a single symmetric segment with complex circumferential boundary conditions. With respect to different nodal diameter numbers, free vibration analyses of the disk assembly were then effectively performed. For calculated resonance conditions, the steady-state responses of the turbocharger bladed disk were computed. By using this coupled CFD–FEM analysis, the dynamic loading of the turbine blades can be determined in the design process.

Maximizing the Natural Frequencies and Transverse Stiffness of Centrally damped, Circular Disks by Thickening the Clamped Part of the Disk

1999 ◽  
Vol 66 (4) ◽  
pp. 1017-1021 ◽  
Author(s):  
A. A. Renshaw
Keyword(s):  
Natural Frequency ◽  
Natural Frequencies ◽  
Vibration Modes ◽  
Rotating Disks ◽  
Design Study ◽  
Nodal Diameter ◽  
Transverse Stiffness ◽  
Vibration Data ◽  
Two Alternatives ◽  
Circular Disks

The natural frequencies and transverse stiffness of centrally damped, circular disks are computed taking into account the flexibility of the central clamp and the thickness of the damped part of the disk. When compared to experimental vibration data, these predictions are more accurate than the traditional, perfect clamping predictions, particularly, for zero and one-nodal-diameter vibration modes. The reduction in natural frequency or transverse stiffness caused by clamping flexibility can be mitigated either by increasing the clamping stiffness or by increasing the hub thickness, defined here as the thickness of the disk sandwiched by the central clamp. A design study of these two alternatives for both stationary and rotating disks shows that increasing the hub thickness is often a more attractive design alternative.

Investigation of Alternate Mistuned Turbine Blades Non-Linear Coupled by Underplatform Dampers

2013 ◽  
Author(s):  
S. Tatzko ◽  
L. Panning-von Scheidt ◽  
J. Wallaschek ◽  
A. Kayser ◽  
G. Walz
Keyword(s):  
Turbine Blades ◽  
Forced Response ◽  
Mode Shapes ◽  
Nodal Diameter ◽  
Frictional Contacts ◽  
Bladed Disk ◽  
Engine Order ◽  
Bladed Disk Assembly ◽  
Last Stage ◽  
Software Code

Freestanding turbine blades have typically low structural damping and thus require additional friction damping devices, such as underplatform dampers. The friction coupling between neighboring blades reduces response amplitude and increases resonance frequency. Along with forced response excitation large blades, especially of last stage, could be excited by fluid structural interaction (flutter). To prevent such excitation alternate mistuned blade patterns are beneficial disturbing traveling waves in the stage. In this paper the influence of alternate mistuning is investigated with a simplified oscillator chain as well as a bladed disk assembly coupled by frictional contacts. It is pointed out that the performance of friction coupling can be improved by alternate mistuning as long as the engine order of the excitation is below quarter of the number of blades. Alternate mistuning causes a mode coupling between two nodal diameter vibration mode shapes allowing for energy transfer. The in-house developed software code DATAR is enhanced and alternate mistuning can be applied to the blades as well as to the damping elements. For validation the DATAR code was applied to an alternate mistuned last stage blade of a Siemens gas turbine and compared with available field engine measurement.

Experimental Modal Analysis of a First Stage Blade in ALSTOM Gas Turbine

2014 ◽  
Vol 624 ◽  
pp. 303-307 ◽  
Author(s):  
Arash Rahmani ◽  
Ahmad Ghanbari ◽  
Ali Mohammadi
Keyword(s):  
Modal Analysis ◽  
Gas Turbine ◽  
Natural Frequencies ◽  
Turbine Blades ◽  
Vibration Modes ◽  
Ansys Software ◽  
Critical Problems ◽  
The Subject ◽  
Laser Digitizer ◽  
Acceptable Agreement

Failures of turbine blades are one of the most critical problems in power generating industry. Among the different failure mechanisms, resonant vibration of blades has a major role and therefore is the subject of many recent research works. Therefore, in this paper, modal analysis of a first stage blade in ALSTOM gas turbine is investigated and natural frequencies and vibration modes of blade are found in various conditions. For this purpose, a cloud-point model of a gas turbine blade has been created using 3D Laser Digitizer. Then the numerical calculation by finite element method using ANSYS software based on experimental test conditions is utilized and Experimental natural frequencies have been obtained. The results show acceptable agreement between the experimental and FEM results.

A Nonclassical Vibration Analysis of a Multiple Rotating Disk and Spindle Assembly

1997 ◽  
Vol 64 (1) ◽  
pp. 165-174 ◽  
Author(s):  
I. Y. Shen ◽  
C.-P. R. Ku
Keyword(s):  
Angular Momentum ◽  
Rigid Body ◽  
Vibration Analysis ◽  
Natural Frequencies ◽  
Spindle Assembly ◽  
Rotating Disk ◽  
Rigid Body Motion ◽  
Body Motion ◽  
Vibration Modes ◽  
Nodal Diameter

This paper studies natural frequencies and mode shapes of a spinning disk/spindle assembly consisting of multiple elastic circular plates mounted on a rigid spindle that undergoes infinitesimal rigid-body translation and rotation. Through use of Lagrangian mechanics, linearized equations of motion are derived in terms of Euler angles, rigid-body translation, and elastic vibration modes of each disk. Compared with a single rotating disk whose spindle is fixed in space, the free vibration of multiple disks with rigid-body motion is significantly different in the following ways. First of all, lateral translation of the spindle, rigid-body rotation (or rocking) of the spindle, and one-nodal diameter modes of each disk are coupled together. When all the disks (say N disks) are identical, the coupled disk/spindle vibration splits into N − 1 groups of “balanced modes” and a group of “unbalanced modes.” For each group of the balanced modes, two adjacent disks vibrate entirely out of phase, while other disks undergo no deformation. Because the out-of-phase vibration does not change the angular momentum, the natural frequencies of the balanced modes are identical to those of the one-nodal-diameter modes of each disk. For the group of the unbalanced modes, all disks undergo the same out-of-plane vibration resulting in a change of angular momentum and a steady precession of the spindle. As a result, the frequencies of the unbalanced modes are significantly lower than those of one-nodal-diameter modes of each disk. Secondly, axial translation of the spindle and the axisymmetric modes of each disk are couple together. Similarly, the coupled motion split into N − 1 groups of “balanced modes” and one group of “unbalanced modes,” where the frequencies of the balanced and unbalanced modes are identical to and smaller than those of the axisymmetric modes of each disk, respectively. Thirdly, the rigid-body motion of the spindle does not affect disk vibration modes with two or more nodal diameters. Response of those modes can be determined through the classical vibration analysis of rotating disks. Moreover, vibration response of the disk/spindle assembly from a ground-based observer is derived. Finally, a calibrated experiment is conducted to validate the theoretical predictions.

Some Remarks on the Dynamic Behaviour of Integrally Shrouded Blade Rows

2011 ◽  
Author(s):  
N. Bachschmid ◽  
S. Bistolfi ◽  
S. Chatterton ◽  
M. Ferrante ◽  
E. Pesatori
Keyword(s):  
Steam Turbine ◽  
Natural Frequencies ◽  
Low Pressure ◽  
Contact Forces ◽  
Mode Shapes ◽  
Torsional Vibrations ◽  
Vibration Modes ◽  
Nodal Diameter ◽  
Blade Row ◽  
Pressure Steam

Actual trend in steam turbine design is to use blades with integral shrouds, for high pressure and intermediate pressure steam turbine sections, as well as also for the long blades of the low pressure sections. The blades are inserted with their root into the seat on the shaft in such a way that the blades are slightly forced against each other in correspondence of the shrouds. In long blades of low pressure stages the forcing can be obtained by the untwisting of twisted blades due to the effect of the huge centrifugal forces. The dynamic behavior of these blade rows is difficult to predict due to the nonlinear effect of the contact forces and due to friction. Different models for the contact are proposed and compared. The resulting natural frequencies of the blade row as a function of the different nodal diameter mode shapes are highly depending on the assumed models. For avoiding resonant conditions with engine order excitations, the natural frequencies must be calculated with good accuracy. Some of the modes of the blade row, typically for the last stage of the low pressure steam turbine, can couple with some vibration modes of the rotor: flexural vibrations of the shaft couple with 1 nodal diameter mode shape of the row in axial direction and torsional vibrations of the shaft couple with the 0 nodal diameter mode in tangential direction. Therefore analyses of lateral and torsional vibrations of low pressure steam turbine shafts require also an accurate analysis of the blade row vibration modes.

Analytical and Experimental Investigation of the Coupled Bladed Disk/Shaft Whirl of a Cantilevered Turbofan

1986 ◽  
Vol 108 (4) ◽  
pp. 567-575 ◽  
Author(s):  
E. F. Crawley ◽  
E. H. Ducharme ◽  
D. R. Mokadam
Keyword(s):  
Analytical Model ◽  
Natural Frequencies ◽  
Equations Of Motion ◽  
Disk System ◽  
Structural Dynamic ◽  
Nodal Diameter ◽  
Coupled Equations ◽  
Bladed Disk ◽  
Shaft System ◽  
The One

The structural dynamics of a rotating flexible blade-rigid disk-flexible cantilevered shaft system is analytically and experimentally investigated. A simple analytical model yields the equations of motion expressed in the rotating frame, which show that the blade one nodal diameter modes dynamically couple to the rigid body whirling motion of the shaft-disk system. The blade modes higher than one nodal diameter are uncoupled from the shaft-disk dynamics. Nondimensionalization of the coupled equations of motion yield the criteria for the propensity and magnitude of the interaction between the bladed disk and shaft-disk modes. The analytical model was then correlated with the results of a structural dynamic experiment performed on the MIT Aeroelastic Rotor, a fan similar in design to a modern high bypass ratio shroudless turbofan. A special whirl excitation apparatus was used to excite both forward and backward asynchronous whirl, in order to determine the natural frequencies of the system. The agreement between the predicted and experimental natural frequencies is good and indicates the possibility of significant interaction of the one nodal diameter blade modes with the shaft-disk modes.

Forced Response Analysis of Mistuned Turbine Bladings

2010 ◽  
Author(s):  
Christian Siewert ◽  
Heinrich Stu¨er
Keyword(s):  
Natural Frequency ◽  
Stiffness Matrix ◽  
Natural Frequencies ◽  
Forced Response ◽  
Response Analysis ◽  
Vibrational Behavior ◽  
Bladed Disk ◽  
Fundamental Model ◽  
Mechanical Models ◽  
Number Of Publications

It is well-known that the vibrational behavior of a mistuned bladed disk differs strongly from that of a tuned bladed disk. A large number of publications dealing with the dynamics of a mis-tuned bladed disk is available in the literature. Nearly all published mechanical models for a mistuned bladed disk consider the mistuning in terms of a perturbation of the mass and/or the stiffness matrix or in terms of a perturbation of the tuned system natural frequencies. Therefore, the possible effect of a damping mistuning is neglected in these models. In this paper, a model of a mistuned bladed disk with a combined damping and natural frequency mistuning is presented. This model is based on the well-known Fundamental Model of Mistuning with a novel extension to include the damping mistuning in a straight-forward way.

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