Jozef Kordík

Performance of Synthetic Jet Actuators Based on Hybrid and Double-Acting Principles

The design of the discussed fluid jet actuator followed two ideas: a double-acting operation of reciprocating pumps, and a hybrid synthetic jet (HSJ) actuation. The entire actuator consists of two basic parts, namely the front (central) and rear chambers, from which fluid is displaced by the opposite sides of the same diaphragm. The actuator operates in a double-acting (antiphase) regime with air as the working fluid. The central chamber generates the standard (zero-net-mass-flux) axisymmetric synthetic jet (SJ), while the rear chamber generates system of several non-zero-net-mass-flux HSJs arranged around the central SJ. A number of variants of HSJs with different geometry were designed, manufactured and tested. Their behavior was investigated experimentally using the smoke visualization, reaction force measurement, hot-wire anemometry, and naphthalene sublimation technique. The tests confirm the efficiency of the present design.

Axisymmetric Synthetic Jet Actuators with Large Streamwise Dimensions

This study analyzes the resonant behavior of synthetic jet actuators with large streamwise dimensions, that is, synthetic jet actuators with nozzle and/or chamber lengths comparable with the sound wavelength. Analytical models that capture the effects of the large streamwise dimensions of the actuators are introduced for natural frequencies, velocity resonance curves, and phase shifts. Velocity measurements were obtained using a hot-wire anemometer at the nozzle outlets of four synthetic jet actuator configurations. The velocity amplitudes and phase characteristics were evaluated from experimental data, and higher-order resonances (up to the fifth order) were revealed. The theoretical natural frequencies, velocity resonance curves, and phase shifts were compared with the experimental results and found to be in qualitative agreement.

Heat and Mass Transfer Caused by a Laminar Channel Flow Equipped With a Synthetic Jet Array

Low Reynolds number laminar channel flow is used in various heat/mass transfer applications such as cooling and mixing. A low Reynolds number implies a low intensity of heat/mass transfer processes since they rely only on the gradient diffusion. To enhance these processes, an active flow control by means of synthetic (zero-net-mass-flux) jets is proposed. The present study is experimental, in which a Reynolds number range of 200―500 is investigated. Measurement has been performed mainly in air as the working fluid by means of hot-wire anemometry and the naphthalene sublimation technique. Particle image velocimetry (PIV) experiments in water are also discussed. The experiments have been performed in macroscale at the channel cross sections (20 × 100) mm and (40 × 200) mm in air and water, respectively. The results show that the low Reynolds number channel flow can be influenced by an array of synthetic jets. The effect of synthetic jets on the heat transfer enhancement is quantified. The stagnation Nusselt number is enhanced by 10―30 times in comparison with the nonactuated channel flow The results indicate that the present arrangement can be a useful tool for heat transfer enhancement in various applications, e.g., cooling and mixing.

Impinging jet-based fluidic diodes for hybrid synthetic jet actuators

A new variant of a fluidic diode for hybrid synthetic jet actuators (HSJAs) is introduced in this paper, namely the diode in the form of a conical duct. The periodic jet flow from the diode impinges on the wall and the resulting flow differences during blowing and suction increase the volumetric efficiency of the actuator. Two alternative definitions of the volumetric efficiency are used. The HSJs velocities and volumetric efficiencies were experimentally evaluated. The experiments were performed using a phase-locked smoke visualization and hot-wire anemometry with air as the working fluid. The diode-to-wall distance and the driving frequency were varied, and the combination of parameters that provided the highest HSJ velocity and highest volumetric efficiency was obtained.Graphical Abstract