Identification of the Dynamic Properties of Active Twist Rotor Model Blade Using Output-Only Data

In this paper, an approach to estimate the dynamic characteristics of a rotating blade using response data is proposed. A test campaign devoted to demonstrate the capability of the Smart Spring device to alter the dynamic properties of the rotating blade is carried out in the framework of the Smart Hybrid Active Rotor Control System, SHARCS, project. The key factor of this project is an active vibration control concept that uses piezoceramic actuators, Smart Spring, to preferentially vary dry friction and stiffness of a structure. This device, if located at the blade root, could adaptively vary the dynamic stiffness of the blade to change its flexural characteristics, thus allowing control of the aeroelastic response of the entire blade. In this paper it is shown how the modal parameters will be estimated from the time histories recorded, by a distributed array of sensors, at different rotational speeds of the blade and for different values of the stiffness of the Smart Spring device. Both time domain and frequency domain methods were applied in order to quantify the effects on the modal properties of different operating conditions of a prototype version of the Smart Spring device. This device was attached to the push rod of an Active Twist Rotor blade developed at the German Aerospace Center (DLR). From the performed experimental investigation, carried out at the DLR’s whirl tower test facility, it was possible to draw the typical fan plots of the rotating blade, from which useful information about the dynamic behavior of the system could be achieved.