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Research Papers: Gas Turbines: Structures and Dynamics

A Test Rig for Noncontact Traveling Wave Excitation of a Bladed Disk With Underplatform Dampers

[+] Author and Article Information
Teresa Berruti

Department of Mechanical Engineering, Politecnico di Torino, Corso Duca degli Abruzzi, 24 10129 Turin, Italyteresa.berruti@polito.it

Christian M. Firrone

Department of Mechanical Engineering, Politecnico di Torino, Corso Duca degli Abruzzi, 24 10129 Turin, Italychristian.firrone@polito.it

Muzio M. Gola

Department of Mechanical Engineering, Politecnico di Torino, Corso Duca degli Abruzzi, 24 10129 Turin, Italymuzio.gola@polito.it

J. Eng. Gas Turbines Power 133(3), 032502 (Nov 11, 2010) (8 pages) doi:10.1115/1.4002100 History: Received May 11, 2010; Revised June 03, 2010; Published November 11, 2010; Online November 11, 2010

This paper presents a static test rig called “Octopus” designed for the validation of numerical models aimed at calculating the nonlinear dynamic response of a bladed disk with underplatform dampers (UPDs). The test rig supports a bladed disk on a fixture and each UPD is pressed against the blade platforms by wires pulled by dead weights. Both excitation system and response measurement system are noncontacting. This paper features the design and the setup of the noncontacting excitation generated by electromagnets placed under each blade. A traveling wave excitation is generated according to a desired engine order by shifting the phase of the harmonic force of one electromagnet with respect to the contiguous exciters. Since the friction phenomenon generated by UPDs introduces nonlinearities on the forced response, the amplitude of the exciting force must be kept constant at a known value on every blade during step-sine test to calculate frequency response functions. The issue of the force control is therefore addressed since the performance of the electromagnet changes with frequency. The system calibration procedure and the estimated errors on the generated force are also presented. Examples of experimental tests that can be performed on a dummy integral bladed disk (blisk) mounted on the rig are described in the end.

Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

The test rig “Octopus”

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Figure 2

The arm structure

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Figure 3

Detail of the electromagnet unit

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Figure 4

(a) Sketch of the electromagnet facing the steel blade. (b) Equivalent magnetic circuit. (c) Simplified equivalent magnetic circuit.

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Figure 5

(a) Measured output current amplitude versus input voltage amplitude for different input voltage frequency. (b) Comparison of admittance values derived from experiments and from RL model.

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Figure 6

Electromagnet calibration bench

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Figure 7

Amplitude voltage versus electrical frequency calibration curves for the 24 electromagnets when Fa=5 N

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Figure 8

Amplitude voltage V versus electrical frequency for EM1 at 5 N, 10 N, and 15 N: experimental curves (solid lines) and estimated (dashed lines)

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Figure 9

FE model of the blisk and detail of the cylindrical underplatform damper

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Figure 10

First two bending families, without UPDs (free condition) and with UPDs constrained between the platforms (stick condition)

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Figure 11

(a) Disk and UPDs loading system. (b) Detail of platforms and UPD.

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Figure 12

24 disk circular ODS, each of them measured with one EM switched on (a) before tuning and (b) after tuning

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Figure 13

Hammer test, FRF blade 1

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Figure 14

FRF in “fully stick” configuration

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Figure 15

Nonlinear FRF for nodal diameter 2

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