Session: 28-02 System Response / Blade-Tip-Timing

Paper Number: 128878

128878 - Modal Identification of Rotating Blades by Tip Timing and Strain Gauge Measurements in Operating Condition 

Rotor blades are critical components in turbo engines as they are subjected to vibration and high-cycle fatigue. Their dynamic behavior strongly depends on the working conditions, including rotor speed, temperature and flow condition. These factors are reproduced in the numerical simulations used during the design, however experimental validation and model updating are necessary steps to construct high-fidelity numerical models and carry out reliability analyses. In this framework, blade tip timing (BTT) has proven a simple, robust, and nonintrusive technique for measuring the dynamic behavior of rotating blades in real operating engine.

The modal identification carried out with such measurement technique enables the evaluation of frequency, amplitude and harmonic index of the vibration whilst less confidence is given to the damping estimation. This is mostly due to the lack of opportunities to validate tip-timing results using more established techniques for modal identification, such as strain-gauge / telemetry systems, that, on the other hand, find few applications on full scaled engines.

In order to support the use of BTT datasets, this paper compares the results of the modal identification of in-operation rotor blades obtained by BTT and strain gauge data. The identification is performed investigating the dynamic response of a bladed disk undergoing to synchronous vibration during the engine run-up or cast-down phases. The Single Degree of Freedom Fit (SDOF) and the Circumferential Fourier Fit (CFF) methods are used for BTT data, whilst an identification procedure based on the time-frequency analysis is applied to the strain-gage data.

The two modal identification strategies are applied first to a disk simulator with known dynamic properties. Then, the comparison is carried out considering the experimental data obtained on an operating last-stage blade of a steam turbine equipped with both BTT and strain gauge systems.

Presenting Author: Roberto Guida Ansaldo Energia

Presenting Author Biography: Roberto Guida is a test and validation engineer working for Ansaldo Energia, in Italy, with several years’ experience in the field of turbomachinery testing on models and full-scaled engine. His major expertise is on vibration analysis of rotating components with profound knowledge of tip timing measurement system.

Authors:

Roberto Guida Ansaldo Energia
Luigi Carassale University of Genova
Michela Marrè-Brunenghi Ansaldo Energia