Damping Properties of Steam Turbine Blades
This section describes a program of tests to examine the damping properties of several types of steam turbine blades. These studies were conducted in a non-rotating damping test rig which used real blades mounted in corresponding real disk root attachment
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DAMPING PROPERTIES OF STEAM TURBINE BLADES
N.F. Rieger Stress Technology Incorporated, Rochester, New York, USA
ABSTRACT
This section describes a program of tests to examine the damping properties of several types of steam turbine blades. These studies were conducted in a non-rotating damping test rig which used real blades mounted in corresponding real disk root Simulated centrifugal loading was attachments. applied to the blades as a lengthwise axial pull. The The rig and the test program are described. damping properties of the blades studied were found to conform primarily to effects associated with The influence of material hysteresis damping. attachment friction appears to be negligible for test loads and vibratory amplitudes encountered in practice. A small level of fluid damping from the gas stream appears to be possible where the blades are subject to working pressure loads.
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Iptroduction
This section describes a series of experiments which were undertaken to determine the nature and magnitude of damping The test program included high in steam turbine blades. pressure blades, intermediate pressure blades, and low pressure blades. The program was undertaken using a special type of test rig, Figure 1, which simulated the blade loading under rotating conditions, by the application of a known preload. A statistically significant number of identical blades were involved in each test. This gave some indication of the amount of test scatter which could result in the damping data under controlled test conditions from differences between blades and their assembly conditions within their root attachments. The tests examined the influence of blade type, attachment root type, surrounding environment (air, steam, vacuum), axial load, mode of vibration, and other factors. N. F. Rieger (ed.), Rotordynamics 2 © Springer-Verlag Wien 1988
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N.F. Rieger
The objectives of this study were: a)
To study the damping properties of several types of steam turbine blades in actual root attachments under simulated operating conditions.
b)
To examine the nature of evident in the test results.
c)
To evaluate the magnitude of the damping from the decay traces for a variety of blade types, root attachment designs, blade lengths, and operating conditions.
d)
To determine the relative contributions of the various damping mechanisms to the total damping under these conditions,
e)
To evaluate the significance of applied root load, vibration amplitude, root type, blade length, and gas environment as possible contributing parameters in each case.
the damping which
is
Details of the test rig used, and of the test conditions and results achieved are given in the following sections. 11.5.2
Previous Blade Damping Studies
There is surprisingly ature on the damp-ing Blade manufacturers relating to materials group performance from
little information in the open literproperties of steam turbine blades, have developed extensive test data performance, and to blades and blade vibration tests.
Grady [1] tested several dumm
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