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Special Section: Honoring Dr. Leroy H. Smith

Aeroelastic Stability Assessment of an Industrial Compressor Blade Including Mistuning Effects

[+] Author and Article Information
Yaoguang Zhai

Siemens Industrial Turbomachinery AB, SE-612 83 Finspong, Swedenyaoguang.zhai@siemens.com

Ronnie Bladh

Siemens Industrial Turbomachinery AB, SE-612 83 Finspong, Swedenronnie.bladh@siemens.com

Göran Dyverfeldt

Siemens Industrial Turbomachinery AB, SE-612 83 Finspong, Swedengoran.dyverfeldt@siemens.com

J. Turbomach 134(6), 060903 (Sep 19, 2012) (12 pages) doi:10.1115/1.4007210 History: Received August 31, 2011; Revised March 01, 2012; Published September 14, 2012; Online September 19, 2012

This paper presents a comprehensive investigation into the aeroelastic stability behavior of a transonic front blade in an industrial compressor when operating outside its normal range of service parameters. The evolution of the airfoil’s aeroelastic stability in the first flexural mode is studied as the front blade operation progresses towards choked flow conditions. First, linearized 3D flutter computations representing today’s industry standard are performed. The linearized calculations indicate a significant, shock-driven flutter risk at these off-design flow conditions. To further explore the aeroelastic behavior of the rotor and to find a viable solution toward flutter risk elimination, two parallel investigations are undertaken: (i) flow perturbation nonlinearity effects and potential presence of limit-cycle oscillation, and (ii) effects of blade mistuning and flutter mitigation potential of intentional mistuning, including its impact on forced response behavior. The nonlinear harmonic analyses show that the minimum aerodynamic damping increases rapidly and essentially linearly with blade oscillation amplitude beyond the linear regime. Thus, a state of safe limit-cycle oscillation is predicted for the fully tuned blade. Additionally, it is found that intentional, realizable blade frequency offsets in an alternating pattern efficiently stabilize the blade. Finally, it is verified that alternating mistuning has a beneficial effect versus the inevitable random mistuning also in the forced response.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

3D view of the investigated front stage compressor rotor

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Figure 2

Evolution of engine output power and 1F reduced frequency with loading parameter

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Figure 3

Midspan meridional view of the employed 2.5-stage CFD grid with every forth grid line shown (a) and steady state relative Mach number distribution for the nominal case LP = 1.0 (b). Two passages per row are shown for profile visibility.

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Figure 4

Employed blade finite element model

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Figure 5

Natural frequency versus nodal diameter characteristics at nominal rotor speed

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Figure 6

Tangential 1F mode shape deflections according to the finite element model (a) and after interpolation onto the CFD grid (b)

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Figure 7

Mode 1F aerodynamic damping versus nodal diameter for different loading parameters, including close-up view of minimum damping region

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Figure 8

Evolution of engine output power and minimum 1F aerodynamic damping with loading parameter

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Figure 9

Steady state relative Mach number distributions along blade chord at 50% span for different loading parameters

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Figure 10

Steady state relative Mach number distributions at 50% span for the nominal case LP = 1.0 (a) and the least stable case LP = 0.85 (b)

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Figure 11

Mode 1F net (PS + SS) aerodynamic work done on the blade per cycle for the nominal case LP = 1.0 (a) and the least stable case LP = 0.85 (b)

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Figure 12

Aerodynamic work done per cycle along blade chord at 50% span for the nominal case LP = 1.0 and the least stable case LP = 0.85

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Figure 13

Comparison of mean relative Mach number distributions along blade chord at 50% span from linear and nonlinear solutions

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Figure 14

Mode 1F aerodynamic damping versus nodal diameter from linear and nonlinear harmonic solutions

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Figure 15

Minimum 1F aerodynamic damping as function of blade oscillation amplitude

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Figure 16

Unsteady pressure amplitude and phase distributions due to 1F motion per % chord amplitude: (a) linear harmonic solution with 1% of chord amplitude; (b) nonlinear harmonic solution with 1% of chord amplitude; (c) nonlinear harmonic solution with 5% of chord amplitude

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Figure 17

Aerodynamic work done per cycle distributions due to 1F motion per % chord amplitude: (a) linear harmonic solution with 1% of chord amplitude; (b) nonlinear harmonic solution with 1% of chord amplitude; (c) nonlinear harmonic solution with 5% of chord amplitude

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Figure 18

Aerodynamic work done per cycle along blade chord at 50% span from linear and nonlinear harmonic solutions

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Figure 19

Evolution of average (solid) and min/max (dashed) mistuned MAC values and eigenfrequency errors versus the number of retained master DOF

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Figure 20

Flutter probability variation with standard deviation of random frequency mistuning for different levels of intentional mistuning

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Figure 21

Tuned and mistuned eigenmode root loci distributions for selected mistuned configurations

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Figure 22

Mode 3 aerodynamic damping versus nodal diameter for different loading parameters

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Figure 23

Envelope of maximum relative forced response amplitudes for selected mistuned configurations

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Figure 24

99.9th percentile response magnification factors versus standard deviation of random frequency mistuning with and without aerodynamic coupling and for varying levels of intentional mistuning

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