Bladed Disk Assembly Research Articles

Vibrations of Bladed-Disk Assemblies—A Selected Survey (Survey Paper)

The progress made in the decade 1973–1983 in the area of vibration of jet engine blades is surveyed. The purpose of the survey is to provide a general review of recent progress and the limited number of references cited can be used to reach the many other important publications in this area. Both structural and aerodynamic aspects of blade vibration are discussed, although the emphasis is on the former. The areas of future analytical and experimental research needed to continue to influence the design of these components are outlined.

Coupled Vibration Analysis for Bladed Disk Assemblies and Flexible Shafts : 1st Report, Irrational Condition

This paper is concerned with coupled vibration between flexible bladed disks and flexible shafts in the application of the Finite Element Method. since a bladed disk is considered as a periodically symmetric structure, it is enough to analyze one periodic substructure of a bladed disk by the use of the Cyclic Symmetry Method. In this paper, it is assumed that only one nodal point at the center of a bladed disk is connected with one nodal point of a shaft. The followings are known through this study. (i) Natural modes of zero nodal diameters generated on a bladed disk are coupled with longitudinal and torsional vibration of a shaft. (ii) Natural modes of one nodal diameter generated on it are coupled with only lateral vibration of a shaft. (iii) Natural modes of more than two nodal diameters generated on it are uncoupled with vibration of a shaft completely.

Natural Frequencies of Rotating Bladed Disks Using Clamped-Free Blade Modes

The problem of calculating the natural frequencies of a practical rotating bladed disk assembly is solved by use of a new dynamic substructuring method employing the free modes of the disk and the clamped-free modes of the blade. The bladed disk may have lacing-wires at any radius. The lacing-wire, or any other general elastic connection element, is assumed to extend around the whole circumference. Hence, the assembly fulfills the requirements for a circumferentially periodic structure. Centrifugal effects are included. The free modes of the disk are used to describe the dynamics of the disk by a 4 × 4 receptance matrix. The row of blades is described by a dynamic stiffness matrix of order 4 + 10l, where l is the number of lacing-wires. The dynamic stiffness matrix of the blading is formed directly from the modes of one single clamped-free blade without any lacing-wire. The lacing-wires are treated as elastic and massless. The zeroes of the resulting transcendental frequency determinant of order 4 + 10l are solved by the sign-count method. The calculation procedure has proved to be very efficient. Further, it enjoys the precious property of being automatic and infallible in the sense that there is no risk of missing any frequency whatever the spacing of natural frequencies. Experimentally found frequencies are compared to calculated ones.

Vibration Analysis on Bladed Disk Assemblies of Axial-flow Turbines

Recently, a turbine blade is becoming wider, thicker and longer, therefore it is not enough to know the vibration characteristics of only a single tirbine blade. In the present paper, the vibration characteristics of bladed disk assemblies of axial-flow turbines are experimentally investigated and calctlated. The natural frequencies and the natural modes of bladed disk assemblies are detected experimentally using the fast Fourier transformation of the measured impulsive force and the acceleration, and they are calculated by a new cyclic symmetry method the authors developed. The results of the calculation are in good agreement with those of the experiment, and it becomes clear that this new cyblic symmetry method is effective for analysis of periodically symmetric structures.

Disc Vibration - Rotating Blade and Stationary Vane Interaction

Only in rare cases does the vibration of a bladed disc assembly give concern for possible fatigue failures due to disc modes. This paper describes cases which should be investigated and outlines methods that can be used to prevent failures. Two types of bladed discs are treated; centrifugal applications with radial blades and those used for axial turbines or compressors. However, the theory is applicable to other discs. Analysis is presented showing cases of significant minor resonances over and above disc critical speeds.

Forced Vibrations of a Single Stage Axial Compressor Rotor

A semi-empirical method, utilizing modal analysis based on experimentally obtained modeshapes has been used to study the vibration response of a 23 bladed axial compressor rotor. The system modeshapes, characterized by the blade deflections at resonance, are more or less irregular depending upon the proximity of the system frequencies to the blade cantilever frequencies. The response of the detuned bladed disk assembly to various types of harmonic excitations are shown to be predictable if sufficient experimental information is available about the resonant modes and frequencies of the system.

An Analytic Study of the Energy Dissipation of Turbomachinery Bladed-Disk Assemblies Due to Inter-Shroud Segment Rubbing

A novel computational method is presented for analytically studying the energy dissipative characteristics of turbomachinery bladed-disk assemblies due to inter-shroud segment rubbing. Coulomb friction, as the dissipative mechanism, is utilized in this method with broader generality than that in other similar studies heretofore. The immediate objectives of this study were 1) to obtain an understanding of the general slippage characteristics of the shroud segment interfaces in the presence of both steady normal (to the shroud segment interfaces) lock-up stresses and stresses due to modal vibration, and 2) to incorporate these characteristics in a calculation of the minimum modal deflection required for incipient slipping as well as an estimation of the energy dissipation (damping) due to subsequent rubbing. The utlimate applications of this knowledge are for more accurate calculations of flutter stability margins and dynamic magnifications of stresses, and for a more rigorous formulation of the shroud boundary conditions used in the calculation of natural frequencies and mode shapes. As a result of this preliminary investigation it is concluded that the energy dissipation due to inter-shroud segment rubbing tends to an amplitude squared dependency and is thus similar to classic structural damping.

Towards the Efficient Vibration Analysis of Shrouded Bladed Disk Assemblies

Prediction of the vibration properties of turbomachine blades and disks is an essential part of turbine design. However, the complexity of modern machines and the necessity to analyze the complete assembly of disk, blades, and shroud combine to make this a lengthy task. This paper describes an investigation aimed at improving the efficiency of such prediction techniques. The assembly is analyzed by studying each component individually and then combining these together with a receptance coupling technique by matching forces and displacements at each connection point. A study is made to establish which of the 6 coordinate directions at each junction need to be included in this process. The results of this study clearly demonstrate the necessity for including certain coordinates while others may be omitted with little loss of accuracy.

Vibration Characteristics of Bladed Disc Assemblies

A study is made to establish the basic vibration characteristics of bladed disc assemblies. An analysis is presented and used to predict the natural frequencies and mode shapes of uniform bladed discs. It is found that there are many more natural frequencies than those indicated by a study of the blade cantilever modes. The effects of blade detuning are studied and found to give rise to irregular and complex modes of vibration. Consideration of the vibration characteristics under typical operating excitation conditions shows that a detuned system is susceptible to many more resonances than is an equivalent tuned system.