Visualization study of hybrid synthetic jets

Abstract

A synthetic jet (SJ) is a fluid flow that is created from an oscillatory process of suction and blowing. A hybrid synthetic jet (HSJ) combines this principle with fluidic pumping through a valveless pump. The present study addresses round HSJs issuing into quiescent surroundings from an actuator orifice 8 mm in diameter. For comparison purposes, a common (zero-net-mass-flux) SJ is used. The working fluid is air, and the maximum Reynolds numbers are 11,000 and 9,000 for HSJs and SJs, respectively. The following five experimental methods are employed: flow visualization using a smoke wire technique, velocity measurements using a hot-wire anemometer, velocity measurements using a Pitot tube, impedance measurements of the actuators, and measurements of the jet momentum using precision scales. Flow visualization demonstrates phase-locked flow fields. The first resonance frequencies are theoretically derived to be 79 and 98 Hz for an SJ and HSJ, respectively. These values are confirmed by all of the experimental methods used. The results demonstrate the advantages of HSJs. The tested HSJ achieves a 24 % higher pumped volume flow rate in comparison to the SJ at a maximum volumetric efficiency of 33 %. Moreover, the overall energy efficiency of the HSJ actuator is 1.8 times higher than that of the SJ actuator. These promising HSJ features, including significantly higher efficiencies, can be useful for various heat transfer applications such as the cooling of highly loaded electronic devices.