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TECHNICAL PAPERS: Gas Turbines: Structures and Dynamics

Experimental Investigation of Mode Shape Sensitivity of an Oscillating Low-Pressure Turbine Cascade at Design and Off-Design Conditions

[+] Author and Article Information
Damian M. Vogt

Chairs of Heat and Power Technology, Royal Institute of Technology, S-100 44 Stockholm, Swedendamian.vogt@energy.kth.se

Torsten H. Fransson

Chairs of Heat and Power Technology, Royal Institute of Technology, S-100 44 Stockholm, Sweden

The values indicated in the parentheses indicate the operating parameter and the abbreviation used hereafter.

Note that the actual outlet Mach numbers (as from flow field averages) were not exactly set to M=0.4, 0.6, and 0.8, respectively. This was kept consistent throughout the tests.

J. Eng. Gas Turbines Power 129(2), 530-541 (Aug 07, 2006) (12 pages) doi:10.1115/1.2436567 History: Received June 20, 2006; Revised August 07, 2006

The effect of negative incidence operation on mode shape sensitivity of an oscillating low-pressure turbine rotor blade row has been studied experimentally. An annular sector cascade has been employed in which the middle blade has been made oscillating in controlled three-dimensional rigid-body modes. Unsteady blade surface pressure data were acquired at midspan on the oscillating blade and two pairs of nonoscillating neighbor blades and reduced to aeroelastic stability data. The test program covered variations in reduced frequency, flow velocity, and inflow incidence; at each operating point, a set of three orthogonal modes was tested such as to allow for generation of stability plots by mode recombination. At nominal incidence, it has been found that increasing reduced frequency has a stabilizing effect on all modes. The analysis of mode shape sensitivity yielded that the most stable modes are of bending type with axial to chordwise character, whereas high sensitivity has been found for torsion-dominated modes. Negative incidence operation caused the flow to separate on the fore pressure side. This separation was found to have a destabilizing effect on bending modes of chordwise character, whereas an increase in stability could be noted for bending modes of edgewise character. Variations of stability parameter with inflow incidence have hereby found being largely linear within the range of conditions tested. For torsion-dominated modes, the influence on aeroelastic stability was close to neutral.

Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 3

Distribution of unsteady pressure measurement locations on the oscillating (top) and nonoscillating blades (bottom)

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Figure 4

Outlet flow traverse data for low subsonic operating point

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Figure 5

Blade loading data at midspan for the three velocity levels at nominal incidence

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Figure 6

Blade loading data at midspan for the three incidence cases at low subsonic flow velocity

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Figure 7

Unsteady blade loading data at midspan on blades +1, 0, and −1; axial bending, low subsonic, nominal inflow, k=0.1

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Figure 8

Unsteady blade loading data at midspan on blades +2 and −2; axial bending, low subsonic, nominal inflow, k=0.1

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Figure 9

Unsteady blade loading data at midspan on blades +1, 0 and −1; circumferential bending, low subsonic, nominal inflow, k=0.1

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Figure 10

Unsteady blade loading data at midspan on blades +1, 0 and −1; torsion, low subsonic, nominal inflow, k=0.1

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Figure 11

Effect of flow velocity on unsteady blade loading data at midspan on blades 0 and −1; axial bending, nominal inflow, k=0.1

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Figure 12

Variation of traveling wave mode stability versus interblade phase angle at k=0.1 (top) and k=0.3 (bottom); low subsonic, nominal inflow

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Figure 13

Stability plot at low subsonic and high subsonic Mach number, nominal inflow, shaded areas mark stable regions, and values display stability parameters

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Figure 14

Effect of inflow incidence on unsteady blade loading data at midspan on blades +1, 0 and −1; axial bending, low subsonic, k=0.1

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Figure 15

Effect of flow incidence on traveling wave mode stability, axial bending, low subsonic, k=0.3

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Figure 16

Effect of reduced frequency (top) and flow incidence (bottom) on blade influence coefficients; axial bending; low subsonic

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Figure 17

Incremental change in stability with inflow incidence; low subsonic, k=0.3; shaded areas mark stabilizing change

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Figure 1

Test object; top: profile sections and modes tested, bottom: passage shape

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Figure 2

Test facility and sketch of test module

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