Measurement of rotor blade structural dynamics

Abstract

Initial results collected with optical fibre Bragg grating (FBG) strain sensors and with a novel direct fibre optic shape sensing approach during a series of ground vibration tests performed on a rotor blade are presented. A number of key benefits highlight the potential of applying the shape sensing system to complex rotor blade structures: (1) no information of the underlying structure is required to infer the shape and (2) the rotor blade structural characterization can be achieved with only one straight fibre optic cable that is mounted along the length of a rotor blade. An assessment of sensor performance has shown that the results are within 4% agreement with commercially available instrumentation systems. Limitations of the use of FBG based strain gauges are discussed in terms of the dependency of strain measurements on the position of neutral axis.