Mechanically Amplified Piezoelectric Microactuators for Laminar-Turbulent Transition Control on Airfoils

Abstract

Drag reduction on airfoils using arrays of micro-actuators is one application of so-called Aero-MEMS. These microactuators interact with TS instabilities (Tollmien-Schlichting waves) inside a transitional boundary layer by superimposing artificially generated counterwaves in order to delay the transition process. These actuators need to exhibit a relatively large stroke at relatively high operational frequencies when operated at high Mach numbers. For this purpose, a novel micromachined mechanical amplification unit for increasing the stroke of piezoelectric microactuators up to high frequencies is proposed. The mechanical lever is provided by a sliced nickel titanium membrane. In this work, the actuator is explained in detail and wind tunnel experiments are carried out to investigate the effect of this mechanically amplified piezoelectric microactuator on thin transitional boundary layers. The experiments have been carried out in the transonic wind tunnel facility of the Berlin University of Technology on an unswept test wing with an NACA 0004 leading edge. The effectiveness of the actuator for flow control applications is determined in an open-loop setup consisting of one actuator having a relevant spanwise extension and a microstructured hot film sensor array located downstream. The aerodynamic results at Mach 0.33 are presented and discussed. It is shown that the actuator influences TS wave specific frequencies between 2.5 kHz and 7.4 kHz. The actuator amplitude is large enough to influence a transitional boundary layer significantly without bypassing the natural transition process which makes this type of micromachined actuator a candidate for high speed TS-control.