Stereo-DIC Measurements of a Vibrating Bladed Disk: In-Depth Analysis of Full-Field Deformed Shapes

Abstract

Vibration measurements of turbomachinery components are of utmost importance to characterize the dynamic behavior of rotating machines, thus preventing undesired operating conditions. Local techniques such as strain gauges or laser Doppler vibrometers are usually adopted to collect vibration data. However, these approaches provide single-point and generally 1D measurements. The present work proposes an optical technique, which uses two low-speed cameras, a multimedia projector, and three-dimensional digital image correlation (3D-DIC) to provide full-field measurements of a bladed disk undergoing harmonic response analysis (i.e., pure sinusoidal excitation) in the kHz range. The proposed approach exploits a downsampling strategy to overcome the limitations introduced by low-speed cameras. The developed experimental setup was used to measure the response of a bladed disk subjected to an excitation frequency above 6 kHz, providing a deep insight in the deformed shapes, in terms of amplitude and phase distributions, which could not be feasible with single-point sensors. Results demonstrated the system’s effectiveness in measuring amplitudes of few microns, also evidencing blade mistuning effects. A deeper insight into the deformed shape analysis was provided by considering the phase maps on the entire blisk geometry, and phase variation lines were observed on the blades for high excitation frequency.

Modal shapes measurements of a rotating disc using stroboscopic 3D digital image correlation and down-sampling strategy

“…Because the false matches of feature points cannot be completely eliminated in this method, it can't be used for accurate full-field initial guess estimation. A reliability-guided displacement tracking (RGDT) strategy is adopted [7]. Full-filed DIC analysis begins with a specified seed point, and only the initial guess of the seed point is needed, which can be solved as previously mentioned.…”

Polymer Materials in Additive Manufacturing: Modelling and Simulation

“…In this way, amplitude in the different range of frequency or displacement magnitude against the time in a certain frequency is achievable. Neri et al [140] described a measurement system to investigate the impeller damping (Figure 7a) by measuring the excitation force during the test with respect to the response and the load amplitude. The vibrational measurements in the high-frequency range of 2568 Hz, 6239 Hz and 6357 Hz showed a harmonic response and frequency values in combination with the low response amplitudes, in the range of 10 µm.…”

Toward Polymeric and Polymer Composites Impeller Fabrication

“…In this way, amplitude in the different range of frequency or displacement magnitude against the time in a certain frequency is achievable. Neri et al [ 140 ] described a measurement system to investigate the impeller damping ( Figure 7 a) by measuring the excitation force during the test with respect to the response and the load amplitude. The vibrational measurements in the high-frequency range of 2568 Hz, 6239 Hz and 6357 Hz showed a harmonic response and frequency values in combination with the low response amplitudes, in the range of 10 µm.…”

“… ( a ) Optical setup of the stereo-digital image correlation measurement and ( b ) Displacement maps for the 6239 Hz excitation frequency (reprinted with permission from [ 140 ]). …”