Development of in-series piezoelectric bending beam bimorph actuators for active flow control applications

Abstract

In addition to physical testing, a quasi-static analytical model was developed and compared with experimental data, which showed close correlation for both free displacement and blocking force. Similarly, finite element analysis was performed on the actuator design to determine the predictability of resonance frequency, again showing good correlation.

Finally, the static and dynamic vortex generator modules were tested on a flat plate in a small subsonic wind tunnel using Stereoscopic Particle Image Velocimetry as the measurement technique. Both time- and phase-averaged flow fields were acquired for the static and dynamic cases. Comparison between the different sets of data showed that there seemed to be no significantly consequential difference between the SVG and DVG (in the time-averaged sense), leading to a recommendation of further investigation.

Successful integration of the devices into active flow control test modules was also achieved. A test module using an in-series actuator to drive a small dynamic vortex generator in a crossflow was designed and fabricated. A parametrically identical static vortex generator module was also created, and served as the basis to which the dynamic vortex generator was compared. Likewise, the actuator design was integrated into a NACA 0015 airfoil to drive a dynamic carbon fiber trip. This test article had the ability to induce stall cells in certain flow regimes, allowing stall cell formation to be observed and analyzed.

To test the reliability of the fabrication process and the actuators themselves, a manufacturing study and endurance testing were performed. Multiple actuators with the same dimensions were constructed, and showed that frequency responses and output forces were very repeatable. The endurance testing showed that the actuator design could run for extended periods of time without any detrimental effects on performance.

Piezoelectric materials have long been used for active flow control purposes in aerospace applications to increase the effectiveness of aerodynamic surfaces on aircraft, wind turbines, and more. Piezoelectric actuators are an appropriate choice due to their low mass, small dimensions, simplistic design, and frequency response. This investigation involves the development of piezoceramic-based actuators with two bimorphs placed in series. Here, the main desired characteristic was the achievable displacement amplitude at specific driving voltages and frequencies. A parametric study was performed, in which actuators with varying dimensions were fabricated and tested. These devices were actuated with a sinusoidal waveform, resulting in an oscillating platform on which to mount active flow control devices, such as dynamic vortex generators or dynamic pins. The main quantification method consisted of driving these devices with different voltages and frequencies to determine their free displacement, blocking force, and frequency response. It was found that resonance frequency increased with shorter and thicker actuators, while free displacement increased with longer and thinner actuators.