Laser Doppler vibrometry experiment on a piezo-driven slot synthetic jet in water

Abstract

Abstract. The present study deals with a slot synthetic jet (SJ) issuing from an actuator into quiescent surroundings and driven by a piezoceramic transducer. The actuator slot width was 0.36 mm, with a drive frequency proposed near the theoretical natural frequency of the actuator. The working fluid was water at room temperature. The present experiments used flow visualization (a laser-induced fluorescence technique) and laser Doppler vibrometry methods. Flow visualization was used to identify SJ formation, to demonstrate its function, and to estimate SJ velocity. Laser Doppler vibrometry was used to quantify diaphragm displacement and refine operating parameters. Phase averaging yielded a spatial and temporal diaphragm deflection during the actuation period. Taking incompressibility and continuity into consideration, the velocity in the actuator slot and the Reynolds number of the SJ were evaluated as 0.21 m/s and 157, respectively. The present results confirmed a SJ actuator function at the resonance frequency of approximately 46 Hz, which corresponds closely with the theoretical evaluation. The laser Doppler vibrometry results corresponded closely with an estimation of SJ velocity by the present flow visualization.

PIV and LIF study of slot continuous jet at low Reynolds number

“…The corresponding Reynolds number is Re = 90. These values are in a good agreement with the parameters of the previously studied SJ [13,14]. Figure 2 shows a typical visualization of the jet (a) in the middle of the actuator slot (x-y plane, z = 0) and (b) along the z-axis (z-x plane, y = 0).…”

“…Figure 8 shows the comparison between the CJ and SJ velocity vector field (z = -15 mm). The SJ is shown in the blowing part of the cycle; more details were described previously - [13,14]. The pulsatile character of the SJ is visible, mainly in the near field (x/(2B) < 10).…”

“…When the device operates as a SJ actuator, the inlet from the pump is closed and the piezoelectric diaphragm is driven by the sinusoidal current with a drive frequency f = 46 Hz and RMS voltage 18.0 V. A choice of the low frequency actuation at the near resonance frequency was refined recently by means of theoretical and experimental approaches -the details can be found in [13], [14]. Moreover, the time-mean exit velocity and the Reynolds number were evaluated in previous experiments [13], [14] as U 0 = 0.17 m/s and Re = 127, respectively.…”

“…Moreover, the time-mean exit velocity and the Reynolds number were evaluated in previous experiments [13], [14] as U 0 = 0.17 m/s and Re = 127, respectively.…”

“…The experimental setup is based on a previously studied piezoelectric SJ actuator (see [13], [14]) which was adapted to be able to work also in a continuous (steady) regime as is described thereinafter. The aim of this study is to verify the possibility of the device to work in continuous regime and also to obtain results which can be used as a benchmark for further experiments with SJs.…”