Final work : Evaluation of optical measurement techniques for testing, correlating and updating turbine engine blades

Abstract

This thesis study focuses on a particular non-contact vibration measurement technique used in the industry: 1D Laser Doppler Vibrometry. This technique measures the vibration in the direction of the laser beam, thus captures only a projection of the phenomenon in 3D. This has been a limiting factor in understanding the real vibration of an object. The main drive of this study is to understand the capabilities and the limitations of this technique; and propose a solution to these limitations. To overcome the limitations arising from measuring tilted or non- at surfaces, a solution method has been proposed. The proposed method requires a single image input from the vibration measurement camera and the computer model of the test object. With this method, measurement coordinate alignment with 3D computer model can be established and the FRF signals can be corrected to obtain normal-to-surface 3D mode shape information. Experiments have been done to investigate the validity and performance of the proposed method. The results showed that the measurements with 1D Laser Doppler Vibrometry follow the theoretical expectations under tilt angles. With this information, the measurement amplitudes could be corrected to derive the normal-to-surface vibrations. However, by increasing the tilt angle coordinate shifts have been observed regarding the alignment of measurement points. The shifts have been related to the LDV device con guration. Unless corrected, the results on non- at surface measurements only give analysis of a nonlinearly shifted coordinate set, which becomes misleading.