Oliver Huxdorf

Effects of Piezoceramic Actuator in Quasistatic Use

In the field of smart structures, piezoceramic actuators are wildly used for vibration reduction and acoustic manipulation of structures. Those applications typically run at frequencies between 10 Hz and 10k Hz. Prominent examples are the piezoceramic actuators implemented in helicopter rotor blades to twist them dynamically for higher harmonic control (HHC) or individual blade control (IBC). Once the actuators are implemented it would be a great benefit to also use them to statically change the blade twist (higher twist for take-off and landing - for higher lift; lower twist for high speed forward flight - for reduced drag). Staying with this example it can be found that sensing the twist displacement is not an easy task at all (see [1, 2]), so it would be most desirable, to use open loop control. In order to do that, the transfer function has to be known accurately. Unfortunately measurements show that the amplitudes for such very low frequencies behavior behave strongly non linear. This paper presents experimental results investigating the influence of the frequency on the amplitude - especially going for frequencies in the lower mHz region. A variety of piezoceramic actuators has been investigated: from stacks to patch type, d33 as well as d31 effect actuators. A second focus of this paper is the reaction of piezoceramic actuators on the application of a constant DC voltage. The drift that occurs has to be taken into consideration. A third focus of this paper is the dependency of a displacement output of such an actuator at a constant applied DC voltage on the voltages that the actuator had seen before. This topic is of special mportance for aerodynamically effective surfaces that are driven by piezoceramic actuators and should be analyzed (generation of polars) in static conditions.

Design and manufacturing of morphing fan blades for experimental investigations in a cascaded wind tunnel

Within this paper shape variable compressor blades for jet engines using piezoelectric composite actuators attached to the blade’s suction and pressure sides are investigated. By applying a voltage to these actuators it is possible to increase and to decrease the blade stagger angle by changing the camber angle. This study is about the engineering process and about the rst results of a cascaded wind tunnel experiment.

Mitigating loads by means of an active slat

An active slat on an airfoil is tested in the wind tunnel to reduce lift fluctuations caused by inflow angle fluctuations. The airfoil with an integrated slat allows to control the gap size between slat and main body. The variation of the gap size leads to dfferent aerodynamic properties. This behavior is investigated in a comprehensive characterization of the aerodynamics for different positions of the static slat and a wide range of angles of attack. A sinusoidal inflow angle fluctuation is generated by an active grid. These fluctuations are causing lift force fluctuations at the airfoil with static slat. The slat gap size then is varied dynamically synchronous to the inflow angle uctuations. Depending on the phase shift between slat gap size variation and inflow angle fluctuation a reduction of the lift force is observed. The slat system is found to be capable of mitigating load fluctuations caused by turbulent inflow.

Smart structures for wind energy turbines

As wind energy turbines are getting larger, the blade root bending loads are becoming a design constraint. Especially loads resulting from the increasing blades masses as well as from turbulences, gusts and even local stall at the inner blade section cause an increase of the fatigue loads. Within the national research project SmartBlades by DLR and its partners from Fraunhofer IWES as well as ForWind Oldenburg and Hannover, which was funded by the Germany Federal Ministry for Economic Affairs and Energy, several active as well as passive technologies are investigated to reduce such loads. As passive means like bend twist coupling offer potential without increasing system complexity, active means promise a higher potential in load reduction with an increase in complexity. This paper is presenting results of two promising active approaches: a flexible trailing edge and a shape-adaptive slat. Both techniques have the potential to reduce blade fatigue loads. The focus of this paper is on the demonstrator hardware, benefits and wind tunnel testing of these techniques.