Actively manipulating flow characteristics around the wing can enhance the high-lift capability and reduce drag;
thereby, increasing fuel economy, improving maneuverability and operation over diverse flight conditions which enables
longer, more varied missions. Active knits, a novel class of cellular structural smart material actuator architectures
created by continuous, interlocked loops of stranded active material, produce distributed actuation that can actively
manipulate the local surface of the aircraft wing to improve flow characteristics. Rib stitch active knits actuate normal to
the surface, producing span-wise discrete periodic arrays that can withstand aerodynamic forces while supplying the
necessary displacement for flow control. This paper presents a preliminary experimental investigation of the pressuredisplacement
actuation performance capabilities of a rib stitch active knit based upon shape memory alloy (SMA) wire. SMA rib stitch prototypes in both individual form and in stacked and nestled architectures were experimentally tested for their quasi-static load-displacement characteristics, verifying the parallel and series relationships of the architectural configurations. The various configurations tested demonstrated the potential of active knits to generate the required level of distributed surface displacements while under aerodynamic level loads for various forms of flow control.
Energy harvesting is a process in which energy which would otherwise be wasted is captured, stored and then used
to power a system. Devices having such capabilities enjoy an extended life particularly advantageous in systems with
limited accessibility, such as biomedical implants and structure embedded micro and wireless sensors. A viable family of
materials for this purpose is piezoelectric materials because of their inherent ability to convert vibrations into electrical
energy. This paper uses a type of pre-stressed PZT-5A Unimorph called Thunder®, to actively convert mechanical
vibrations into useable power. The effects of temperature, 20-100°C, pressure, 138-345kPa, frequency, 2-5Hz, and load
resistance, 0.47-2.0M&OHgr;, on the energy harvesting potential of the device are studied. The data obtained is analyzed using
statistical techniques that assess the significance of the factors being studied. Results showed that the effect of
temperature by itself on the voltage, AC or DC, and power generation was seen to be not significant. In combination
with other factors such as pressure, frequency, and load resistance however, the temperature effect becomes statistically
significant. These interaction effects tend to reduce voltage and power conversion. The maximum DC voltage and power
were calculated as 108V and 11641&mgr;W at 20°C, 275.8kPa, 2.5Hz and 2M&OHgr;. Similarly the greatest peak to peak AC
voltage of 338V was also measured at 20°C and 2.5Hz. Based on the geometry of the piezoelectric diaphragm the most
power density was evaluated to be 15&mgr;W/mm3.
Piezoelectric diaphragms are used as synthetic jets because of their size, rapid time response, and relatively low power consumption. Among the piezoelectric diaphragms used are unimorphs and Bimorphs. In this study, a bimorph diaphragm, a thin Unimorph pre-stressed device and a Radial Field Diaphragm (RFD) are compared. A bimorph consists of two bonded PZT discs, a thin Unimorph pre-stressed device consists of copper, PZT, and stainless steel and a Radial Field Diaphragm consist of a layer of PZT with inter-digitized electrodes encapsulated in Kapton film. The effects of driving waveform on jet velocity are studied for each of these actuators. The actuators are driven at varying frequencies and the differential pressure in the cavity is monitored.