Research Papers: Gas Turbines: Structures and Dynamics

Novel Dynamic Rotor and Blade Deformation and Vibration Monitoring Technique

[+] Author and Article Information
Thorsten Pfister, Philipp Günther, Florian Dreier

Jürgen Czarske

 Technische Universität Dresden, Laboratory for Measurement and Testing Techniques, Helmholtzstrasse 18, 01062 Dresden, Germanyjuergen.czarske@tu-dresden.de

J. Eng. Gas Turbines Power 134(1), 012504 (Nov 07, 2011) (7 pages) doi:10.1115/1.4004160 History: Received April 15, 2011; Accepted April 20, 2011; Published November 07, 2011; Online November 07, 2011

Monitoring rotor deformations and vibrations dynamically is an important task for improving both the safety and the lifetime as well as the energy efficiency of motors and turbo machines. However, due to the high rotor speed encountered in particular at turbo machines, this requires concurrently high measurement rate and high accuracy, which is hardly possible to achieve with currently available measurement techniques. To solve this problem, in this paper, we present a novel nonincremental interferometric optical sensor that measures simultaneously the in-plane velocity and the out-of-plane position of laterally moving objects with micrometer precision and concurrently with microsecond temporal resolution. It will be shown that this sensor exhibits the outstanding feature that its measurement uncertainty is generally independent of the object velocity, which enables precise deformation and vibration measurements also at high rotor speed. Moreover, this sensor does not require an in situ calibration and it allows a direct measurement of blade velocity variations in contrast to blade tip timing systems. For application under harsh environmental conditions such as high temperatures, a robust and miniaturized fiber-optic sensor setup was developed. To demonstrate the capability of this sensor, measurements of tip clearance changes and rotor blade vibrations at varying operating conditions of a transonic centrifugal compressor test rig at blade tip velocities up to 600 m/s are presented among others.

Copyright © 2012 by American Society of Mechanical Engineers
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Figure 1

Two interference fringe systems with monotonously increasing (top) and decreasing (bottom) fringe spacing in axial direction z are shown, which are superposed in the same location inside of the measurement volume in practice

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Figure 2

Functional principle of the laser Doppler distance sensor (LDDS)

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Figure 3

Modular and fiber-optic setup of the LDDS [16]

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Figure 4

Experimentally obtained standard position uncertainties σz are shown, which were obtained for the tooth tip position of a rotating brass toothed wheel with 40 mm radius and 2 mm tooth width (simulating a bladed rotor) at varied rotation speed. For a commercial triangulation sensor, the position uncertainty increases steadily with increasing circumferential speed v, whereas σz remains approximately constant for the LDDS at a value slightly above 1 μm.

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Figure 5

Top: schematic of the configuration of the 3-point measurement system for measuring the size, i.e., the radius R, and the position, i.e., the location (xc ,yc )T of the center of mass, of a rotating cylinder simultaneously. Bottom: picture of the experimental setup showing the test rotor (steel cylinder) and the LDDS sensors attached to the top cover of the test rig.

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Figure 6

Dynamic displacement of the center of rotation, i.e., the center of mass, (xc ,yc )T of the cylindrical steel rotor in xc - and yc -directions measured at a rotation speed of 2000 rpm. The solid black lines represent regression curves [20].

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Figure 7

Two-dimensional map of the wobbling motion of the rotor calculated from the time domain data of Fig. 6. The solid black line represents a regression curve for visualizing the wobbling motion [20].

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Figure 8

Measured wobbling magnitudes represented by the standard deviations of the center of mass in dependence on the rotational speed

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Figure 9

Measured radial enlargements of the test rotor as a function of its rotational speed in comparison with a quadratic regression curve

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Figure 10

Compressor section of the test rig at the German Aerospace Center (DLR) in Köln with the mounted laser Doppler probe (LDDS)

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Figure 11

Standard position uncertainty σz for a single rotor blade as a function of the rotor speed [17]

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Figure 12

Position time series (left) and corresponding Fourier spectra (right) measured with the LDDS on a single rotor blade for five different rotation speeds between 30,000 rpm and 50,000 rpm

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Figure 13

Blade tip clearance changes at varying mass flux of the centrifugal compressor test rig measured at 50,000 rpm with the LDDS in comparison with a capacitive reference probe [17]




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