Lab-scale experimental validation of a piezoelectric energy harvesting lag damper

Currently the lifespan of helicopter rotor blades is determined based on a conservative lifetime calculation. This leads to blades being discarded while they still possess a significant residual amount of flighthours. Blade health monitoring systems are desired to actively track the strains in the blade as a means to determine the residual life of the blade, significantly extending the technical life expectancy. A major drawback is the need for an electrical infrastructure to transmit all the signals to and from the rotor hub to the aircraft body. It would be advantageous if the required power could be generated locally. Within the European Clean Sky project vibrationbased power harvesting is chosen as a solution to powering in-blade health monitoring systems. In this paper simulations of a new power harvesting concept are validated experimentally. Local generation of power will allow for a ‘plug and play’ rotor blade and signals may be logged or transmitted wirelessly to the body of the aircraft. Examples are the blade strains, hinge forces, vibrations and so on. At the ERF2011 [1] presented a simulation model to predict the electrical output of a lag damper augmented with a piezoelectric based energy harvester. Simulations indicated that for an 8.15m blade the output is to be around 5W. The concept includes a piezo electric stack mounted in the damper rod and in series with the damping element. All forces generated by the damper are also passed through the stack and through the piezo electric effect electric charge is generated. Through the use of advanced circuits the power is conditioned and can be stored in a large capacitor or battery located in the rotor hub. The concept is validated in the lab. The setup consists of a large stroke shaker delivering a high force at low frequency. A piezoelectric stack with a large pre-stress is used so that it can also cope with the tensile forces generated by the damper. A viscous damper which has no dead zone upon reversal of the motion is used to mimic the lag damper. Although the damper does not possess a similar damping profile as an actual lag damper this does not pose a problem as the peak force is more important than the exact profile. Lastly a laser vibrometer, a force sensor, a thermocouple and a voltmeter are utilized to log relevant data through a SigLab system. A number of experiments are conducted to verify the simulation model. Following individual component experimentation, different electrical circuits are coupled to the stack and each result is then compared to a simulation of the respective electrical configuration. Two circuits are to be validated: Direct Current Impedance Matching is used as it is a passive circuit and the ‘standard’ for power harvesting and Synchronous Switch Harvesting on Inductor is used as it is shown to be the best performing circuit investigated in previous simulations [2]. The desired end result is an experimentally validated simulation model of the lag damper - harvester model which can be used to predict power output of similar power harvesting systems