Optical Rotor-Blade Deformation Measurements using a Rotating Camera System

Abstract

The knowledge of the movements and the deformation of rotor blades is of great importance for the performance and the safe operation of a rotor system, especially for blades with a high aspect ratio like on helicopters or wind turbines. To measure these parameters in the rotating system is not easy, because the number of sensors is limited due to their impact on the aerodynamics and the modification of the structure. Strain gauge measurements can furthermore directly be affected e.g. by the choice of the sensor location and temperature effects. To avoid those problems and in addition enable direct shape measurements contactless optical methods have still been applied to rotor and propeller deformation measurements in the past. These attempts have been done out of the rotating frame observing either only small rotors or the blade passing within the field of view. DLR and Hardsoft developed a rotating 3D image acquisition system for helicopter rotors and performed first tests on the whirltower of Airbus Helicopters in Donauwörth (GER). The system is mounted on the hub and co-rotates with the rotor. It is able to record images of the whole blade at each azimuth angle. Those images later are processed with an IPCT software tool and deliver the continuous 3D surface shape and location of the observed blade. From the comparison of the 3D surfaces for different recordings, the bending and torsion of the blade can be obtained. The paper will briefly describe the rotating camera system itself, the non-intrusive deformation measurement method IPCT and the measuring setup. The presentation of the recorded images, the obtained data and a discussion of the measurement results will conclude the paper. The lessons learned from the presented campaign will be helpful for manufacturers in the design and measurement of their future rotor systems.