| Popis: |
Detailed measurements of the velocity field in a synthetic jet emanating from a piezoelectric actuator are conducted. A two-dimensional, steady, turbulent jet is synthesized from the ambient air by periodically deflecting a piezoelectric-driven disk, enclosed in a cavity. The cavity is sealed all around, with only a two-dimensional slot, 0.5 mm wide and 30 mm long, on one side. The actuator is excited with square and sinusoidal waveforms, and the time-dependent velocity is measured with a hotfilm anemometer over a wide range of excitation frequencies and spatial locations. Time-averaged values and useful statistics are then computed from these data. It is found that two distinct regions exist in the flow-field created by the actuator. Close to the slotexit, the mean centerline velocity accelerates to a maximum at a distance of approximately 12 slotwidths. The flow is unsteady, and is dominated by large velocity fluctuations induced by the oscillating membrane. At axial distances larger than approximately 12 slot-widths, the flow pattern changes. At greater distances it appears as a steady jet where the flow is no longer affected by the oscillating membrane. The jet exhibits properties that are indicative of a fully developed, twodimensional, turbulent jet. * Visiting Researcher, on Sabbatical from the Israeli Armament Development Authority ^ Research Engineer, Senior Member AIAA # Assistant Professor, Associate Fellow AIAA This paper is declared a work of the U.S. Government and Is not subject to copyright protection in the United States. Measurements of the centerline velocity, at various excitation frequencies, show that there are two resonance frequencies at which the mean exit velocity is maximized. The two resonance frequencies are 700 Hz and 1160 Hz. When the actuator is excited with a square wave, the corresponding mean velocities are 8.7 m/s and 7.0 m/s. When excited with a sinusoidal wave at the same frequencies, the actuator produces mean velocities of 7.7 m/s and 5.0 m/s. Nomenclature b D d E f ma T t U(t) |
