Pressure Loading of Piezo Composite Unimorphs
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Pressure Loading of Piezo Composite Unimorphs Poorna Mane1, Karla Mossi1 and Robert Bryant2 1 Virginia Commonwealth University, Richmond VA 23284, U.S.A 2 NASA Langley Research Center, Hampton VA 23681, U.S.A. ABSTRACT Over the past decade synthetic jets have emerged as a promising means of active flow control. They have the ability to introduce small amounts of energy locally to achieve non-local changes in the flow field. These devices have the potential of saving millions of dollars by increasing the efficiency and simplifying fluid related systems. A synthetic jet actuator consists of a cavity with an oscillating diaphragm. As the diaphragm oscillates, jets are formed through an orifice in the cavity. This paper focuses on piezoelectric synthetic jets formed using two types of active diaphragms, Thunder® and Lipca. Thunder® is composed of three layers; two metal layers, with a PZT-5A layer in between, bonded with a polyimide adhesive. Lipca is a Light WeIght Piezo Composite Actuator, formed of a number of carbon fiber prepreg layers and an active PZT-5A layer. As these diaphragms oscillate, pressure differences within the cavity as well as average maximum jet velocities are measured. These parameters are measured under load and no-load conditions by controlling pressure at the back of the actuator or the passive cavity. Results show that the average maximum jet velocities measured at the exit of the active cavity, follow a similar trend to the active pressures for both devices. Active pressure and jet velocity increase with passive pressure to a maximum, and then decrease. Active pressure and the jet velocity peaked at the same passive cavity pressure of 18kPa for both diaphragms indicating that the same level of pre-stresses is present in both actuators even though Lipca produces approximately 10% higher velocities than Thunder®. INTRODUCTION Methods that attempt to control the motion of fluids have been extensively explored in the past. Some of these methods can be passive or active or both [1]. Passive flow control is usually achieved using steady state tools such as wing flaps, spoilers, and vortex generators, among others. These techniques though effective have marginal power efficiency and are not capable of adjusting to the instantaneous flow conditions experienced during flight. Active flow control (AFC) methods however, are much more efficient as they can adapt to the constantly changing conditions by introducing small amounts of energy locally to achieve non-local changes in the flow field with large performance gains [2,3,4]. The simplification of conventional high lift systems by AFC could possibly lead to providing 0.3% airplane cost reduction, up to 2% weight reduction and about 3% cruise drag reduction [5]. In spite of all the advantages, using active flow control devices usually adds complexity in design, and increases manufacturing and operation cost of the system preventing their use. For this reason, many researchers have focused on designing better active flow control devices t
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