111 / 2021-03-30 19:50:36

Observation of centrifugal hardening effect of rotating blades based on digital image correlation

Rotating blade,digital image correlation,centrifugal hardening effect

Wind turbine dynamics and control

With the centrifugal effect caused by rotation, the natural frequencies of rotating blades increase with the increase of rotating speeds. Such phenomenon has been studied by researchers for decades with measures of creating theoretical models and numerical calculation methods, but rarely through operational tests due to the limitation of measurement techniques.  With the newly proposed Phase Mapping Method which enhanced the robustness of digital image correlation when used on rotating objects, operational tests are performed on a beam-like blade when rotating at different speeds. Through the extraction of the out-of-plane responses with the excitation of an air pump, the natural frequencies of a such blade are obtained and hence the centrifugal hardening effect is observed. The quality of the obtained data is high as the measurement is done in a non-contact fashion which brings no additional mass and the number of measured points is large which leads to more detailed description of the continuous object.