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Research Papers: Gas Turbines: Structures and Dynamics

Pre-optimization of Asymmetrical Underplatform Dampers

[+] Author and Article Information
Chiara Gastaldi

DIMEAS,
Politecnico di Torino,
Torino 10129, Italy
e-mail: chiara.gastaldi@polito.it

Muzio M. Gola

DIMEAS,
Politecnico di Torino,
Torino 10129, Italy
e-mail: muzio.gola@polito.it

1Corresponding author.

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received June 18, 2016; final manuscript received June 22, 2016; published online August 16, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(1), 012504 (Aug 16, 2016) (9 pages) Paper No: GTP-16-1229; doi: 10.1115/1.4034191 History: Received June 18, 2016; Revised June 22, 2016

The numerical coupled optimization of an underplatform damper is the exploration of its dynamics through a finite element model which includes both the damper and the blades. This is an effective approach if the initial damper mass and geometry have been previously selected (i.e., pre-optimized) in such a way that those parameter combinations leading to undesirable damper behavior are ruled out a priori: —ensure that damper jamming is avoided by ruling out the undesirable combinations of platform and friction angles; —ensure that damper lift-off is avoided through an appropriate choice of the shape and position of the damper-platform flat contact surface and the position of the damper mass center; —set upper and lower to the value of damper-platform contact forces (as a multiple of the damper centrifugal force), the first being related to friction and wear problems, and the second to the very existence of bilateral contacts. The above is strongly dependent on the effective values of friction coefficients, which can vary by a factor of over two with temperature, frequency and contact pressure. The paper illustrates the pre-optimization procedure using, as an example, a rigid bar damper with a curved-flat cross section. In order to validate the method against experimental data and to determine the necessary real contact parameters, the paper capitalizes on already developed tools presented in the previous ASME papers: the test rig developed at the AERMEC lab, the numerical model representing the damper dynamics, and the automatic random sampling tuning procedure.

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Figures

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Fig. 1

(a) Curved-flat damper configuration. Parameters θR, θL, and h are variables to be selected through the pre-optimization process, (b) damper configuration selected after the pre-optimization process, and (c) nonoptimized damper configuration presented in Ref. [3].

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Fig. 2

Damper equilibrium to rotation and resulting position of the left contact force for OP and IP phase motion. On the right, the corresponding force equilibrium for OP and IP slipping motion.

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Fig. 4

IP pre-optimization maps for h/r=0.2 and μL=μR equal to (a) 0.3, (b) 0.5, and (c) 0.7

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Fig. 5

Experimental setup: the left platform is connected to the piezoelectric actuators capable of reproducing IP and OP motion. The right platform is connected to the force sensors and the damper is pulled by a deadweight simulating the centrifugal force. A laser head measures the platforms' relative displacement and damper kinematics.

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Fig. 6

Hysteresis and rotation signal comparison for two different damper configurations under the same experimental conditions

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Fig. 8

(a) Measured and simulated hysteresis at 80 Hz and increasing values of centrifugal load and (b) corresponding friction coefficients estimated values as a function of the centrifugal load

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Fig. 7

(a) Measured and simulated hysteresis at 5 Hz and increasing values of centrifugal load and (b) corresponding friction coefficients estimated values as a function of the centrifugal load

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Fig. 9

(a) Measured and simulated hysteresis at CF = 8.65 kg 9.81m/s2=84.9 N and increasing values of excitation frequency and (b) corresponding friction coefficients estimated values as a function of excitation frequency

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