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.

Energetic efficiencies of synthetic and hybrid synthetic jet actuators driven by electrodynamic transducers

“…The advantages of the HSJA are evident: For P e = 0.4-3.2 W, the HSJA achieves a 15-23% increase in the velocities and a 41-48% increase in the energetic efficiency. These results well agree with the previous experiments with the same actuator, which were performed at a bit higher input real power, P e = 4.0 W, see [43,48,55]. Namely, the studies [43, 48, and 55] concluded that the HSJA achieves a 25%, 24%, and 26 % increase of the velocities in comparison with the SJA, respectively.…”

“…An important parameter that is going to be observed in this study is the efficiency of the SJA. A generalized version of the energetic efficiency definition from [48] will be used. The generalization dwells in the extension of the definition for non-uniform velocity profiles and in relating the mean fluid kinetic energy rate to the input real power,…”

“…The present synthetic/hybrid synthetic jet actuator (SJA, HSJA) operates with air as the working fluid, and its geometry and electrical connection is identical as in [43], [48], [55]. A sketch of the actuator is shown in Fig.…”

“…An experimental evaluation of the Persoons definition was performed by Feero et al [54], who evaluated the efficiency for three actuators with different cavity shapes at actuating frequencies close to the Helmholtz resonance frequency. A more appropriate definition of the SJA efficiency was first introduced by Broučková and Trávníček [48]. Assuming top-hat velocity profiles the authors defined the efficiency as ratio of the fluid kinetic energy rate to the apparent electric power (the power factor was negligible in their study).…”

“…The goal of the current paper is to generalize the definition of SJA/HSJA efficiency from [48] also for non-uniform velocity profiles and arbitrary periodic power inputs. These efficiencies along with characteristic velocities are then investigated for SJA and HSJA based on similar geometries.…”