Piezoelectric Actuators for Synthetic Jet Applications

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Piezoelectric Actuators for Synthetic Jet Applications 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 Synthetic jets have been identified and utilized widely in airflow control applications. These jets of air are usually created by the use of compressed air, or an electromechanically driven vibrating platform. All of these approaches produce desired results in airflow-control such as enhanced lift and increased maneuverability. Despite the results however, system weight, size, response time and force limit their use in aircraft applications where space is a premium. The objective of this study is to characterize the relevant properties for the design of a synthetic jet utilizing three types of piezoelectric actuators as mechanical diaphragms. The limiting parameters of the actuators for this application are shape and volumetric space. Thus, the actuators were circular with a diameter of 6.35 cm, and overall device cavity volume no larger than 147.5 cm3 on a 7 cm x 7 cm areal coverage. The actuators tested were pre-stressed curved metallic unimorphs, bimorphs, and radial field diaphragms. These piezoelectric elements were chosen because of their geometry, quasi-isostatic topography and overall free-displacement. Each actuator was affixed about its perimeter in a cavity, and relevant parameters such as clamped displacement, and jet velocity though a pre-determined dimensional slot, were measured. INTRODUCTION Piezoelectric actuators have been in existence for several decades, however, their application as part of complete mechanisms, machines, or devices are rare. One of the main reasons for failure to find a suitable application for these devices are the boundary conditions dictated by the environment that the device would be used [1, 2]. Piezoelectric actuators such as moonies [3], rainbows [4, 5], unimorphs [6], thunders [7,8,9], and bimorphs [10,11] have been investigated and their properties and behavior are well documented. Predicting their performance in an application however, is still not available, especially when working with circular actuators. A new type of circular actuator with inter-digitated electrodes, radial field diaphragms, RFD, has been designed and characterized [12,13]. Preliminary work shows that RFDs have properties that may be key in an application design. The overall objective of the project is to use these active diaphragms in a synthetic jet cavity no larger than 7.62 cm x 7.62 cm x 2.54 cm. Relevant parameters such as clamped displacement, frequency, and capacitance were measured in a previous study and the limitations and advantages were described [14]. These preliminary results showed that none of the three actuators possessed all of the characteristics needed to design a synthetic jet to be used for an effective flow control mechanism. Synthetic jets as means of flow control devices have been proven to be effective as means to provide flow control reducing drag and