An Electromagnetic System for the Non-Contact Excitation of Bladed Disks C.M. Firrone & T. Berruti Received: 1 December 2010 / Accepted: 26 April 2011 / Published online: 12 May 2011 # Society for Experimental Mechanics 2011 Abstract In this paper a non-contact excitation system based on electromagnets is described. The system aims at exciting cyclically symmetric structures like bladed disks by generat- ing typical engine order-like travelling wave excitations that bladed disks encounter during service. Detailed description of the analytical formulation for the electromagnets sizing, quality assessment and practical implications of the final assembly for the bladed disk excitation are addressed. In particular, the paper proposes an original method to setup the excitation system in order to perform step-sine controlled force measurements. This feature is necessary when non- linear forced response must be measured on bladed disks in order to characterize the dynamic behaviour at different level of excitation. Typical applications of the designed excitation system are two: the first is the study of the effect of a force pattern characterized by a particular engine order on the forced response of mistuned bladed disks, the second is the characterization of intentional non-linear damping source occurring, for instance, for friction phenomena in presence of shrouds or underplatform dampers. Keywords Noncontact excitation . Electromagnet . Bladed disks . Mistuning . Nonlinear . Dynamics Introduction Rotating components of turbo-machinery convert the energy of a fluid passing through the blade arrays of rotors into mechanical work (turbine) and vice versa (compres- sors). Basically, two main features of the bladed disk design concerning the dynamic response must be considered. On one hand the single rotor is subjected to an excitation pattern where each blade is loaded with a series of pulses within a complete disk rotation. The number and the intensity of pulses depend on the architecture of the engine preceding the rotor (number of combustion chambers, stages, stator vanes) and the wide spectral content is usually characterized by several harmonic components whose excitation frequencies on each blade are mainly a multiple of the rotor angular speed. The integer number which, multiplied by the rotor angular speed, gives the blade excitation frequency is known as engine order index (eo). On the other hand, a rotating disk is nominally character- ized by cyclic symmetry properties where one fundamental sector constituted by the blade and its associated disk sector is repeated for a number of times around the rotation axis. The periodical repetition of geometric and material features (tuned system) generates a particular dynamic behaviour of the disk where natural frequencies, and corresponding modes, can be grouped into families featuring the same deformed shape of the vibrating blades or disk [1]. The dynamic study of the bladed disk through FE models benefits of this property since the modal analysis or the forced response calculation of the whole rotor can be performed by processing the mass and stiffness matrices of a single FE sector by applying cyclic symmetry boundary conditions at the interfaces shared with the contiguous sectors [2]. The bladed disk behaviour is obtained in post- processing by expanding the results of the fundamental sector to the real configuration. The main objective at design stage is to avoid any match of the rotor natural frequencies with the excitation frequencies of the harmonic components of the load spectrum which thus shorten the life of the component C.M. Firrone (*) : T. Berruti Department of Mechanical Engineering, Politecnico di Torino, Corso Duca degli Abruzzi, 24, Torino, Italy e-mail: christian.firrone@polito.it T. Berruti e-mail: teresa.berruti@polito.it Experimental Mechanics (2012) 52:447–459 DOI 10.1007/s11340-011-9504-1