Micromachined acoustic resonators for micro jet propulsion

Abstract

The thrust produced by synthetic jets designed for micro jet propulsion is discussed. The proposed propulsion system consists of synthetic wall jets located at the throat of an ejector shroud that are powered by Hehnholtz-type acoustic resonators. The theory of acoustic resonators is described and the thrust produced by the resonators calculated. Theoretical results of the exit velocity and thrust are in good agreement with experimental measurements obtained using particle image velocimetry (PIV) in an axisymmetric synthetic jet. Theoretical results are shown to predict well the resonant frequency of a 1O:l scale model of a micromachined resonator. The thrust produced by the micro scale devices is discussed. It is shown that the micro scale devices could be used as propulsion units for Micro Airborne Platforms (MAP). INTRODUCTION There is a great deal of interest on micro scale jets capable of producing large impulse for application to flow control and propulsion. Streaming produced by a large amplitude acoustic field can be used to produce a synthetic jet stream. A very attractive feature of synthetic jets is that the mean mass flow at the source is zero and therefore the jet stream is produced without the need for an air supply. Several investigations have documented the flow field associated with acoustic streaming.‘.’ Synthetic jets have also been implemented $ Graduate Research Assistant, Department of Aerospace Engineering, Member ALU. l Associate Professor, Department of Aerospace Engmeerlng, Senior Member ALU. t Graduate Research AssIstant, Department of Electrical Engineering and Computer Science. : Professor, Department of Electrical Engmeenng and Computer Science. Copyright Q 2000 LUIS P Bemal, Published by the Amencan lnstltute of Aeronautxs and Astronautics, Inc. with permission Helmcho REXMlat Erector Shroud FCC Flow out Thrust Enhancement