Synthetic Jet Actuator Research Articles

Active control of flow over a rounded ramp by means of single and double adjacent rectangular synthetic jet actuators

Active control of flow over a rounded ramp with Re=13,700 was studied numerically by using rectangular synthetic jet actuators. Wall-resolved large eddy simulation was utilized to accurately predict the separation and reattachment of the flow. The solution of uncontrolled case as well as controlled by a single synthetic jet in quiescent conditions were validated against available numerical or experimental data. To investigate active flow control, five actuated cases were considered: a single synthetic jet (SS), double synthetic jets with opposite-phase actuation (DS opposite-phase), double synthetic jets with in-phase actuation (DS in-phase), a wide synthetic jet (WSS) with the same momentum coefficient of the DS in-phase but with twice the opening width, and a high momentum single synthetic jet (HSS) similar to SS but with twice the momentum coefficient of DS in-phase. The aim was to compare the flow control efficiency of these cases and identify the most effective configuration. The DS opposite-phase case was identified in previous studies as being able to keep the expelled fluid inside the near-wall region. We found that among the first three cases, the DS in-phase was the most effective in reducing the length of the separated region. In order to illuminate the flow control mechanisms of each case, phase-averaged streamlines of the flow were generated. Also, a passive scalar variable was introduced into the flow to allow for tracking the expelled fluid from the synthetic jets. This passive scalar was used to evaluate and compare the flow control mechanisms in the cases of WSS and HSS. We found that HSS was the most efficient mechanism among the five configurations studied.

Atmospheric-pressure pulsed plasma actuators for flow control: shock wave and vortex characteristics

Pulsed plasma actuators are used for an active flow control application since the 2000s. In this paper, we discuss shock wave and vortex characteristics in pulsed plasma actuators after an introduction of research progress on atmospheric-pressure discharge plasma actuators. First, the shock wave characteristics in surface dielectric barrier discharge (SDBD) actuator operating in diffuse-like and multi-streamer modes are discussed. In the most general case, a shock wave in a diffuse-like SDBD actuator is stronger and faster than in a multi-streamer SDBD actuator. Improved plasma actuators, such as the three-electrode SDBD actuator and the plasma synthetic jet actuator have the enhanced shock wave characteristics. Second, in order to investigate the effects of pulse parameters on the shock wave characteristics in nanosecond-pulse SDBD actuator, a particle image velocimetry system is used to capture the formation of starting vortexes at different pulse rise times, pulse durations, and pulse repetition frequencies (PRFs). It is shown that the velocity of a starting vortex significantly increases when the pulse rise time decreases from 400 ns to 50 ns due to a more significant hydrodynamic effect generated during a shorter rise time. This phenomenon is confirmed by calculating a reduced electric field E/N at a short rise time, which turns out to be higher at a shorter rise time than that at a relatively longer rise time. It is also shown that the velocity of a starting vortex increases and its active area enlarges when the PRF increases.

A Study on the Hydrodynamic Characteristics of a Synthetic Jet Propelled Underwater Vehicle

In this article, the drag characteristics of an underwater vehicle propelled by a synthetic jet (SJ) is numerically studied. The underwater vehicle studied is REMUS Autonomous underwater vehicle (AUV). The cruising speed studied is up to 10 knots. The actuation parameters of the SJ actuator are the same under different cruising speeds. When the SJ actuator works, the drag of the vehicle changes periodically. The SJ-induced additional pressure drag increases with increasing cruising speed. The additional friction force is negligible. The thrust of the actuator decreases with increasing cruising speed. The thrust outputted by the SJ actuator when used for underwater vehicle propulsion is smaller than the thrust of an isolated actuator. The mathematical model of the additional drag, the model of the thrust, and the velocity distribution is given to assist the analysis in this article. 1. Introduction The advance in propulsion technique is the key to the evolution of underwater robots. The most common method for underwater robot propulsion is using screw propellers. Thrust is generated through the high speed rotation of the blades. The fluid is accelerated not only in the axial direction but also in the radial direction; however, only fluid acceleration in the axial direction can generate thrust. A significant part of the energy is wasted in the radial direction without thrust generation. As a result, the efficiency of screw propellers is low. Furthermore, the protruded screw propellers induce significant added resistance. This further reduces the total hydrodynamic efficiency of the vehicle. Nature always inspires the technical revolution in engineering. In nature there exist many marine creatures such as squids adopting jet propulsion. The jet created by squids is called pulsed jet. On the other hand, the jet of screw propellers is called steady jet. Studies about pulsed jet showed that compared with the steady jet, pulsed jet possess higher propulsion efficiency (Krueger 2001; Krueger & Gharib 2003, 2005; Moslemi & Krueger 2010; Lydia et al. 2011; Robert & John 2013). Seikman (1963), Weihs (1977), and recently Krueger and Gharib (2003) have shown that pulsed jets can give rise to a greater average thrust than steady jets of an equivalent mass flow rate. Lydia A. Ruiz, Robert W. Whittlesey, and John O. Dabiri found through experiment that pulsed jet has a propulsion efficiency that is 40% higher than that of steady jet, and a drag-based hydrodynamic efficiency increase more than 70% (Lydia et al. 2011). The mechanism behind this high efficiency is the formation of the vortex. The vortex will induce a radial velocity gradient at the nozzle exit. The velocity distribution becomes more ununiform compared with steady jet. As a result, the pressure at the nozzle exit will increase. This is observed by Krueger through experiment.

A Nanosecond Pulsed Generator With Fast-Solid-State Switch for Synchronous Discharge in Plasma Synthetic Jet Actuators

The plasma produced by a pulsed generator is an efficient tool for an airflow control. In this paper, a nanosecond pulsed generator constructed with a fast solid-state switch is designed for triggering synchronous discharges in plasma synthetic jet (PSJ) actuators connected in series. The generator delivers high-voltage pulses with a peak voltage varying from 0 to 20 kV, a rise time of 20 ns, a full-width at half-maximum of 200 ns, and a wide range of pulse-repetition rate varying from 0 to 5.5 kHz. It is proved that this generator is able to trigger synchronous discharges in three PSJ actuators in atmospheric air with a peak discharge current more than 90 A and a deposited energy per pulse of 39 mJ. A schlieren system is used to observe the airflow dynamics, which shows the high synchronization among the three PSJ actuators with a time triggering delay of about 20 ns. The synchronous operation of three PSJ actuators produces a plasma jet with a maximum velocity of 60 m/s and a precursor wave with a velocity of 350 m/s.

Qualitative effect of velocity ratio on the behaviour of a circular synthetic jet flush mounted on a torpedo model in quiescent and cross-flow conditions

A synthetic jet on a curved surface and at high velocity ratios is of immense interest for its possible usage in a torpedo or other naval applications. However, despite exhaustive research on synthetic jets on a flat surface in cross-flow, very few studies have been conducted on synthetic jets on a torpedo-like surface. This study experimentally explores a synthetic jet mounted on a torpedo shaped model in quiescent and cross-flow conditions. The synthetic jet actuation mechanism consists of a motor driven eccentric cam, which oscillates the diaphragm and generates synthetic jet. Initially, the synthetic jet is characterized for two different diaphragm displacements and at four distinct actuation frequencies in the range of 1 Hz – 6 Hz in a quiescent flow environment. Subsequently, similar study is carried out in cross-flow for three different cross-flow velocities ranging from 7.2 – 32 cm/s, at a fixed amplitude of diaphragm oscillations. The flow visualization results qualitatively indicate that the vortex rings in synthetic jet can be classified into two major groups: stretched vortex rings and distorted tilted vortex rings. The flow structures primarily depend on the velocity ratio, which is function of actuation frequency and cross-flow velocity. At a low velocity ratio, the leading vortex is followed by a strong trailing jet. Two distinctly different trajectories are observed for the leading and trailing vortices at higher velocity ratios. At a low cross-flow velocity and higher actuation frequency, synthetic jet leads to increase in the velocity within the boundary layer on the upstream side of the orifice.

Increasing the power efficiency of rotors at transitional Reynolds numbers with synthetic jet actuators

Increasing the power efficiency of rotating energy systems such as wind turbines and gas turbine rotors is critical to deriving more energy from wind or fossil fuels. In this experimental study, thrust-power and laser Doppler velocimetry measurements were made on a sub-scale three-bladed rotor containing an S809 airfoil and 60 piezoelectric-based synthetic jet actuators. The rotor was operated at rotational speeds between 250 and 1250 rpm (RPM) and blade pitch angles of 0, 3, and 6 degrees. It was found that activating 20 synthetic jets per blade reduces the net power input to drive the rotor by up to 10.6% at a rotational speed of 500 RPM and blade pitch angle of 3 degrees. It was also shown that rotor performance parameters; figure of merit and thrust coefficient also increased by up to 28% and 9% respectively. Chordwise velocity measurements reveal that synthetic jets reduce velocity deficit within the boundary layer improving the blade’s sectional lift coefficient and thrust. A correlation is made between the blade tip vortex Reynolds number and spanwise velocity measurements, which indicates that the tip vortex becomes more turbulent and induces an adverse pressure gradient with increasing rotor speed and blade pitch angle. The results indicate that synthetic jets are a viable means of improving the power efficiency of a rotor with vortex Reynolds numbers under 1.8 × 105.

Forced Flow Reattachment Process and the Effect of Pressure Gradient

Stereo particle image velocimetry experiments were conducted to explore the flowfield resulting from the interaction of finite-span synthetic jet actuators and a turbulent boundary layer over an S817 airfoil at various angles of attack. Three specific scenarios were investigated: a favorable pressure gradient, an adverse pressure gradient, and a separated flow in which the synthetic jet actuators reattached the flow. Multiple coherent vortical structures were shed during the reattachment process, for which the circulation associated with these structures was composed of the “trapped” vorticity within the separated shear layer. The shedding of this vorticity was shown to be an inherent part of the reattachment mechanism. In a smaller, local measurement domain, volumetric flowfields were reconstructed near the synthetic jet orifice. It was shown that the presence of an adverse pressure gradient resulted in an increase of momentum diffusion through the boundary layer, in addition to the rate at which the jet’s axis switching occurred. At the highest angle of attack tested, where the flow was reattached through actuation, the coherent structures associated with the synthetic jet dissipated significantly quicker spatially, as much of the energy associated with the actuation was used to maintain attached flow.

Flow characteristics of two-dimensional synthetic jets under diaphragm resonance excitation

Purpose This paper aims to experimentally study the external flow characteristic of an isolated two-dimensional synthetic jet actuator undergoing diaphragm resonance. Design/methodology/approach The resonance frequency of the diaphragm (40 Hz) depends on the excitation mechanism in the actuator, whereas it is independent of cavity geometry, excitation waveform and excitation voltage. The velocity response of the synthetic jet is influenced by excitation voltage rather than excitation waveform. Thus, this investigation selected four different voltages (5, 10, 15 and 20 V) under the same sine waveform as experiment parameters. Findings The velocity field along the downstream direction is classified into five regions, which can be obtained by hot-wire measurement. The first region refers to an area in which flow moves from within the cavity to the exit of orifice through the oscillation of the diaphragm, but prior to the formation of the vortex of a synthetic jet. In this region, two characteristic frequencies exist at 20 and 40 Hz in the flow field. The second region refers to the area in which the vortices of a synthetic jet fully develop following their initial formation. In this region, the characteristic frequencies at 20 and 40 Hz still occur in the flow field. The third region refers to the area in which both fully developed vortices continue traveling downstream. It is difficult to obtain the characteristic frequency in this flow field, because the mean center velocities (ū) decay downstream and are proportional to (x/w)−1/2 for the four excitation voltages. The fourth region reveals variations in both vortices as they merge into a single vortex. The mean center velocities (ū) are approximately proportional to (x/w)0 in this region for the four excitation voltages. A fifth region deals with variations in the vortex of a synthetic jet after both vortices merge into one, in which the mean center velocities (ū) are approximately proportional to (x/w)−1 in this region for the four excitation voltages (x/w is the dimensionless streamwise distance). Originality/value Although the flow characteristics of synthetic jets had reported for flow control in some literatures, variations of flow structure for synthetic jets are still not studied under the excitation of diaphragm resonance. This paper showed some novel results that our velocity response results obtained by hot-wire measurement along the downstream direction compared with flow visualization resulted in the classification of five regions under the excitation of diaphragm resonance. In the future, it makes valuable contributions for experimental findings to provide researchers with further development of flow control.

Numerical Investigation of Dimensionless Numbers on Macro-scale Synthetic Jet Actuator in Quiescent Flow

Numerical Investigation of Dimensionless Numbers on Macro-scale Synthetic Jet Actuator in Quiescent Flow

Measurement of a Temperature Field Generated by a Synthetic Jet Actuator using Digital Holographic Interferometry

This paper shows the possibility of the measurement of a temperature field generated by heated fluid from a synthetic jet (SJ) actuator. Digital holographic interferometry (DHI) was the main measuring method used for the experiments. A single-projection DHI was used for the visualization of the temperature field as an average temperature along the optical axis. The DHI results are compared with data obtained from constant current anemometry (CCA) experiments for the validation of the method. Principle of 3D temperature distribution using a tomographic approach is also described in this paper. A single SJ actuator, multiple continual nozzle, and the SJ actuator with two output orifices are used as a testing device for the presented experiments. The experimental configuration can measure high-frequency synthetic jets with the use of a single slow-frame-rate camera. Due to the periodic character of the SJ flow, synchronization between the digital camera, and the external trigger driving the phenomenon is performed. This approach can also distinguish between periodic and random parts of the flow.

Experimental investigation on thermal and flow characteristics of synthetic jet with multiple-orifice of different shapes

The impingement heat transfer characteristics of a multiple-orifice synthetic jet of circular, oval and diamond orifice shapes are investigated experimentally at different Stokes number, normalized axial distance and pitch ratio. In this study, particle image velocimetry (PIV) based measurements are also undertaken to better understand the underlying flow characteristics of multiple-orifice synthetic jet and to support the associated heat transfer data. The average Nusselt number (Nuavg) obtained with multiple-orifice synthetic jet is up to 75% higher than a single orifice synthetic jet using the same input power to synthetic jet actuator. For larger pitch ratio (R > 1.25), the maximum value of Nuavg is observed to be reduced and obtained closer to heated surface. Multiple-orifice configurations with diamond shape exhibited better thermal performance as compared to other shapes examined in the study. The multiple-orifice configurations with one and two satellite orifices demonstrated two local peaks in Nuavg and are observed only with smaller values of pitch ratio. The location of these local peaks illustrated very little or no dependence on Stokes number (S). Configurations with no center orifice exhibited significantly lower heat transfer as compared to the configurations with center orifice as well as the case with single center orifice. The secondary maxima in Nuavg are entirely missing in the configurations with no center orifice. The PIV data reveals interactions between the adjacent synthetic jets in multiple-orifice case to form a combined synthetic jet with better mixing characteristics as compared to a single orifice synthetic jet and therefore the former exhibits higher heat transfer rate. The PIV data further illustrated the individual behavior of synthetic jets resulting from satellite orifices in multiple-orifice configurations with no center orifice. In addition to heat and flow characteristics of multiple-orifice synthetic jet, the heat transfer correlations are also developed from the experimental data for different orifice shapes. The study of multiple-orifice synthetic jet presented here is expected to be useful in designing the cooling modules for electronic devices.

Application of flow control strategy of blowing, synthetic and plasma jet actuators in vertical axis wind turbines

The vertical axis wind turbines (VAWTs), as common wind turbines for harvesting wind energy, have wide prospects of development. However, the VAWTs are periodically influenced by dynamic stall which can cause the aerodynamic losses and load fluctuation. Therefore, the VAWTs urgently require flow control technique to improve the aerodynamic characteristics. The jet actuators, as active flow control (AFC) techniques, are reasonable implementations for VAWTs. The current paper presents the review of jet flow control techniques which have been used or are worth being used in VAWTs, including the blowing, synthetic and plasma jet actuators. However, the jet flow control strategies to reduce the energy or matter consumption of jet actuators for VAWTs should be developed. Based on the validation of computational model, the VAWTs with upward-parabola blowing jet flow control strategy which can suppress the flow separation in advance was numerically investigated at different tip-speed ratios. The results show that the upward-parabola blowing control strategy can dramatically enhance the aerodynamic performance by using significantly low energy or matter consumption. Obviously, this novel control strategy customized for VAWT can be applied in other jet actuators, improving the aerodynamic performance of VAWT.

The control of flow separation: Study of optimal open loop parameters

Effective parameters in active flow control (AFC) have been studied to clarify a perspective of AFC. In particular, NACA0015 airfoil has been chosen for this study. Fluidic devices such as a synthetic jet actuator (SJA) have been considered because these can enforce two main control parameters of AFC, frequency and momentum ratio, but fluidic excitation with complete blowing and suction cycle was applied with the harmonic excitation as the boundary condition. Flows around the NACA0015 airfoil were simulated for a range of operating conditions. Attention was paid to the active open loop control for the flow separation of the airfoil with SJA at different angles of attack and flap angles. A large number of simulations using unsteady Reynolds averaged Navier-Stokes and large eddy simulation models were performed to study the effects of momentum ratio (Cμ) in the range of 0% to 11% and non-dimensional frequency, F+, in the range of 0–2 for the control of flow separation at the various angles of attack. The optimum value of Cμ as well as F+ was evaluated and discussed. The computational model predictions showed good agreement with several experimental data available such as NASA Langley, Texas A&M, and Clarkson University. It was observed that different angles of attack and flap angles have different requirements for the minimum value of the momentum coefficient, Cμ, for the SJA to be effective for control of separation. It was also found that the variation of F+ noticeably affects the lift and drag forces acting on the airfoil. An intuitive analogy was introduced to evaluate the optimum momentum ratio in AFC, and the results of the optimum momentum ratio have been presented in comparison with available literature data.

Influence of internal orifice geometry on synthetic jet performance

The periodic ingestion and ejection of fluid through an orifice yield vortex rings forming an unsteady jet. The ability to impart momentum with a zero net mass flux makes synthetic jet actuators coveted components in flow control applications. Previous studies underlined the influence of geometrical parameters on synthetic jet evolution. This investigation introduces the orifice lip ratio as a new geometric variation that can influence the performance of the jet. We assess the sensitivity of synthetic jet efficiency to this parameter. Comparisons of test configurations establish the lip ratio as a pivotal parameter and indicate noticeable differences in the exit velocity. The results also highlight the dependence of the jet formation criterion on the orifice lip ratio. The analysis conclusively demonstrates the significance of the orifice lip ratio in the design and optimisation of synthetic jet actuators.

Effect of velocity ratio on the interaction between plasma synthetic jets and turbulent cross-flow

Plasma synthetic jet actuators (PSJAs) are particularly suited for high-Reynolds-number, high-speed flow control due to their unique capability of generating supersonic pulsed jets at high frequency (${>}5$ kHz). Different from conventional synthetic jets driven by oscillating piezoelectric diaphragms, the exit-velocity variation of plasma synthetic jets (PSJs) within one period is significantly asymmetric, with ingestion being relatively weaker (less than $20~\text{m}~\text{s}^{-1}$) and longer than ejection. In this study, high-speed phase-locked particle image velocimetry is employed to investigate the interaction between PSJAs (round exit orifice, diameter 2 mm) and a turbulent boundary layer at constant Strouhal number (0.02) and increasing mean velocity ratio ($r$, defined as the ratio of the time-mean velocity over the ejection phase to the free-stream velocity). Two distinct operational regimes are identified for all the tested cases, separated by a transition velocity ratio, lying between $r=0.7$ and $r=1.0$. At large velocity and stroke ratios (first regime, representative case $r=1.6$), vortex rings are followed by a trailing jet column and tilt downstream initially. This downstream tilting is transformed into upstream tilting after the pinch-off of the trailing jet column. The moment of this transformation relative to the discharge advances with decreasing velocity ratio. Shear-layer vortices (SVs) and a hanging vortex pair (HVP) are identified in the windward and leeward sides of the jet body, respectively. The HVP is initially erect and evolves into an inclined primary counter-rotating vortex pair ($p$-CVP) which branches from the middle of the front vortex ring and extends to the near-wall region. The two legs of the $p$-CVP are bridged by SVs, and a secondary counter-rotating vortex pair ($s$-CVP) is induced underneath these two legs. At low velocity and stroke ratios (second regime, representative case $r=0.7$), the trailing jet column and $p$-CVP are absent. Vortex rings always tilt upstream, and the pitching angle increases monotonically with time. An $s$-CVP in the near-wall region is induced directly by the two longitudinal edges of the ring. Inspection of spanwise planes ($yz$-plane) reveals that boundary-layer energization is realized by the downwash effect of either vortex rings or $p$-CVP. In addition, in the streamwise symmetry plane, the increasing wall shear stress is attributed to the removal of low-energy flow by ingestion. The downwash effect of the $s$-CVP does not benefit boundary-layer energization, as the flow swept to the wall is of low energy.

Characterization of Impingement Heat/Mass Transfer to the Synthetic Jet Generated by a Biomimetic Actuator

Two biomimetic synthetic jet (SJ) actuators were designed, manufactured, and tested under conditions of a jet impingement onto a wall. Nozzles of the actuators were formed by a flexible diaphragm rim, the working fluid was air, and the operating frequencies were chosen near the resonance at 65 Hz and 69 Hz. Four experimental methods were used: phase-locked visualization of the oscillating nozzle lips, jet momentum flux measurement using a precision scale, hot-wire anemometry, and mass transfer measurement using the naphthalene sublimation technique. The results demonstrated possibilities of the proposed actuators to cause a desired heat/mass transfer distribution on the exposed wall. It was concluded that the heat/mass transfer rate was commensurable with a conventional continuous impinging jets (IJs) at the same Reynolds numbers.

Thrust and flow characteristic of double synthetic jet actuator underwater

In this paper, underwater thrust vectoring method based on double synthetic jet actuator is studied. The thrust characteristic of the system under different nozzle distances and phase lags are numerically investigated. The numerical method is validated using data in the literature. The average normal thrust increases when nozzle distance increases. The average tangential thrust decreases when nozzle distance increases. The jet interacts with each other strongly under small nozzle distances. When the two actuators are far enough, the interaction between adjacent jets is negligible. The average normal thrust keeps nearly invariant when phase lag varies. The average tangential thrust increases when phase lag increases from 0 to π and decreases when phase lag increases from π to 2π. The variation of the thrust vectoring angle has the same tendency with the average tangential thrust. The velocity vector and the vorticity contour are given. The mathematical model of the average normal and average tangential thrust is also established.

Intermittent round jet controlled by lateral pulse-modulated synthetic jets

A round air jet was actively controlled by a pair of lateral control jets. The control jets were generated by a pair of opposing synthetic jet actuators, which were driven by the pulse-modulated sinusoidal signal. Two carrier frequencies were tested, namely 160 Hz and 840 Hz. Moreover, control jets driven by un-modulated sinusoidal signals were also tested. An unforced continuous jet was used as the reference case, and for all cases, the Reynolds number of the main round jet was 1570 (related to the nozzle exit diameter of 10 mm). Experiments (flow visualization and hot-wire anemometry) revealed that the flow control caused a suppression of the jet core and a more rapid jet flow decay. In addition, the pulse modulation caused jet intermittency that was distinguished by the periodicity of the time-averaged and fluctuating velocity components. For the case of the lower carrier frequency of 160 Hz, a flapping motion of the controlled jet occurred and the jet formed a zigzag pattern.

On the flow physics and vortex behavior of rectangular orifice synthetic jets

Synthetic jet actuators possess a continuous jet like behavior in its far region and have found wide-scale engineering applications since it allows momentum transport to the flow system without any net mass transfer across the flow boundaries. The case of a non-axisymmetric synthetic jet is particularly significant since it is affected by the differential shear layer at the orifice exit, that depends on its aspect ratio. However, despite exhaustive research on both continuous and synthetic jets, very few studies have experimentally investigated the case of rectangular orifice synthetic jets, focusing on the effect of aspect ratio of the orifice as well as the actuation frequency upon the vortex behavior and the flow physics. In particular, the intriguing phenomenon of vortex bifurcation has mostly been reported only for an individual vortex or for a plain jet. Yet, in a train of vortex rings, such as that obtained in a synthetic jet, the occurrence of vortex bifurcation can be expected, although the flow physics in the wake of individual vortex rings is significantly different. The present study experimentally investigates a rectangular orifice synthetic jet at different orifice aspect ratios and actuation frequencies, focusing on exploring the conditions at which vortex bifurcation occurs, through LIF imaging and Hot-film measurements. The primary objective of these experiments is to provide a qualitative physical insight into the synthetic jet ejected from a rectangular orifice (through LIF imaging), as well as to quantitatively explore the experimental conditions that promote different flow structures (through velocity time trace, time-averaged velocity profiles and power spectral density measurements), particularly the bifurcation of vortex rings. Our experiments indicate that the phenomenon of vortex bifurcation is observed during the axial switching of vortex rings, but only in a narrow range of experimental conditions. Further, the velocity measurements have ascertained that the two prominent reasons behind this bifurcation process are a large disparity in the velocities of the vortex core and the center of vortex ring, as well as the time lag in which the separation distance between the counter-rotating vortices decrease gradually to zero.

On evolution of flow structures induced by nanosecond pulse discharge inside a plasma synthetic jet actuator

Detailed phase-lock schlieren measurement was conducted to study the physical evolution process of the structures inside the plasma synthetic jet actuator driven by a high voltage nanosecond pulse. One strong blast wave and heat source core are generated immediately after the arcing discharge. Within the cavity, as the blast wave is reflected by the cavity walls and interacts with the heat source core, the pressure of the gas inside the cavity is increased rapidly and a series of diffractive wave comes out from the orifice of the cavity, followed by a train of vortex rings and a high speed jet.