Synthetic Jet Actuator Research Articles

Influences of trailing-edge synthetic jets on longitudinal aerodynamic characteristics of a flying wing aircraft

For realizing the nice aerodynamic maneuverability of flying wing aircrafts (FWAs), a longitudinal aerodynamic control technology based on circulation control (CC) using trailing-edge synthetic jet actuators was proposed. Influences on longitudinal characteristics of a FWA were investigated. Results show that synthetic jets could improve the lift, drag, and nose-down moment, having potential of flight control at entire area of attack of angles (AOAs). Cl increment dips and then rises with the growth of AOAs, reaching the minimum at AOA of 12°. The maximum percentage of Cl enhancement and ΔCl/Cμ is separately 64.5% and 50.74%, respectively. Before 12°, synthetic jets could narrow the area of “dead zone,” improve flow velocities along the upper surface, and then move the trailing-edge separation point and the leading-edge (LE) stagnation point downward, enhancing the circulation. Moreover, synthetic jets grow rapidly through entrainment of the local flow, leading to the improvement of valid camber and, hence, the increase in Cl. CC efficiency decreases with the augmentation of AOAs, and leading-edge vortex (LEV) is weakened, causing the drop of Cl increment. After 12°, synthetic jets could enhance the longitudinal velocity of LEV and reduce the swirling number, improving the strength and stability of LEV, which results in larger suction near the leading edge. Moreover, the strengthened LEV could promote flow mixing and then weaken reverse pressure gradients along the wing section, thus improving flow velocities and CC efficiency at the wing section. It is above two factors that make Cl increment rise after 12°.

Effects of dual synthetic jets on longitudinal aerodynamic characteristics of a flying wing layout

A novel method of flight control based on dual synthetic jets (DSJ) is proposed and applied to a large-sweep flying wing aircraft with a hybrid flow mode of leading-edge vortex (LEV) and spanwise separation. An array of dual synthetic jet actuators (DSJAs) is placed along the leading edge to explore its aerodynamic control characteristics and control mechanism. The comparison with synthetic jets (SJ) is implemented to show the differences. Results show that DSJ could delay stalling angle of 6° and promote Cl with greater increments at large attack of angles (AOAs). At AOA of 36°, there was an obvious increase of 23.12% in Cl. Cd decreases at small AOAs, while augments sharply when AOA is larger than 26°. Nose-up moment could be improved. Above features indicate that leading-edge DSJ is not only a nice method of lift enhancement but also an efficient way of flight control. In the fuselage section, DSJ has functions of strengthening LEV, delaying the LEV breakdown and even regenerating LEV at large AOAs, which enhances the bleeding and improves the ability of resisting the reverse pressure gradient, thus totally suppressing the separation and forming the larger leading-edge suction. In the wing section, DSJ acts as a “LEV generator”. Reconstructed LEV could interact with the initial spanwise separation, emerging a hybrid flow mode of “streamers” and “rollers”, in which flow energy could be augmented and separation is partly suppressed. The comparison with SJ supports that the larger leading-edge suction and stronger LEV could be achieved by DSJ, which generate greater increments of Cl and Cm. Maximum Cl increments achieved by DSJ and SJ are respectively 23.12% and 16.91% of Cl without control, meaning DSJ has the higher applying potential in flight control with the same energy consumption.

Numerical study of a liquid cooling device based on dual synthetic jets actuator

This study focuses on an efficient and innovative cooling technology to improve thermal performance of high heat flux electronics. This paper proposes a novel liquid cooling active heat dissipation device based on a dual synthetic jets actuator (DSJA). The heat transfer mechanism and flow mechanism of DSJA in the channel are studied through 3D CFD numerical simulation. Then the influence of inlet flow rate, jet orifice diameter, and diaphragm frequency on the cooling device are analyzed. Heat transfer and pressure drop are significantly influenced by the inlet flow rate when DSJA is off. DSJA has an excellent cooling capacity in the inlet flow range of 0.6–6 L/min after DSJ is on. The actuator with a water inlet turned on shows better heat transfer than the actuator without a water inlet. Increasing the diaphragm frequency from 15 Hz to 80 Hz enhances the heat transfer slightly and has little effect on pressure drop. The hydraulic thermal performance of DSJ before and after opening is 1.263, which verifies the high efficiency of DSJA for liquid cooling.

Characteristics of a Fluidic Oscillator with Low Frequency and Low Speed and Its Application to Stall Margin Improvement

Active flow control methods are commonly used in expanding the operating range of compressors. Indeed, unsteady active control methods are the main focus of researchers due to their effectiveness. For constructing an unsteady active control system, reliable actuators are significant. To compare with conventional actuators such as synthetic jet actuators and rotating valves, fluidic oscillators have structurally robust characteristics and can generate self-excited and self-sustained oscillating jets, which leads to its higher applicability in compressors under severe working conditions. Thus, to explore the feasibility of unsteady active control systems by the usage of fluidic oscillators, a low-frequency and low-speed oscillator is first designed and experimentally studied for improving the stability of a low-speed axial flow compressor. During the experiments, a special casing is designed to install 15 uniformly distributed oscillators in the tip region of compressor. Based on the unsteady micro injections of the rotor tip with rotor rotation frequency, the results indicate that the frequency/period of oscillators are flexible, in which the values are decoupled with the variation of inlet pressure. When the inlet-to-outlet pressure ratio of the oscillator is in the range of 1.1~2.0, the maximum velocity ranges from 30 m/s to 80 m/s. Moreover, the mass flow rate of the single oscillator only varies from 0.017‰ to 0.059‰ from the designed compressor mass flow rate. For the improvement of the compressor stall margin, the value is 3.45% when the total mass flow of oscillators is 0.08% of the designed compressor mass flow.

Flow and heat transfer characteristics of single and multiple synthetic jets impingement cooling

In this paper, the comparison between synthetic jet actuator with single axisymmetric orifice and multiple axisymmetric orifices is presented. The aim of this paper is to compare the flow and heat transfer characteristics of single and multiple synthetic jet impingements cooling. The multiple orifice configurations had a central orifice and a satellite orifices placed in the pitch circle. The synthetic jet actuator had central orifice with 0, 3, 4, 5 and 6 orifices placed in the diameters of the relative pitch circle p/d = 2.5, 3 and 4. A total of 13 various geometric configurations were tested experimentally. In the multiple orifice configurations, the total cross-section area was approximately equal to the cross-section area of the single orifice configuration. The input power delivered to the synthetic jet actuator was maintained constant and equal to 3.00 W. The synthetic jet actuator energetic efficiency, Reynolds number, equivalent Reynolds number, radial and axial distributions of pressure coefficient, and heat transfer characteristic were presented. The synthetic jet issuing from multiple orifice plate merged at some axial distance, creating a single axisymmetric jet. The merging jet axial distances were determined for all investigated configurations. In the present paper, the integral quantities averaged over all orifices cross section area, or over impingement plate much larger than total orifices area, were analyzed for the purpose of objective comparison. From all various investigated parameters obtained from five different and independent experimental methods, the following conclusion may be made: if the total orifice cross section area in the case of single and multiple orifice synthetic jet is similar and real power deliver to the SJA is maintained at the same level the resulting equivalent Reynolds number and equivalent dimensionless stroke length achieved similar values and the impinging jet equivalent Nusselt number also achieved comparable values and distributions.

Investigations on the Interfering Factor of Single Synthetic Jet Actuator on Improving the Efficiency of Wing Control Surface

After the deflection of the wing control surface, flow separation is easily generated at the trailing edge of the wing, which will reduce the lift coefficient and the control surface efficiency. The rudder of the wing is aileron. If the lift generated by the wing is used to improve the efficiency of the control surface, the flow separation caused by the deflection of the control surface must be restrained. Using synthetic jet to change the flow state of boundary layer is the main method to solve the problem of flow separation. Synthetic jet actuator (SJA) has the advantages of no energy loss and simple structure. In this paper, a method of using synthetic jet actuator to suppress the flow separation at the rear of the wing when the aileron deflects is proposed, and the lift coefficient is obtained. The increase of aileron efficiency is calculated by the change of lift coefficient. The EPPLER555 wing with aileron deflection angle of 3°~9° is simulated, and the changes of lift coefficient and aileron efficiency under corresponding working conditions are obtained. The results show that the average lift coefficient of the wing is 0.5 when the deflection angle of the aileron is 3°~9° without SJA. After SJA employed, the lift coefficient will be greatly improved, and the control surface efficiency of EPPLER555 wing will be effectively improved, the lift coefficient will increase by about 20% to 0.6-0.7. For example, when the deflection angle of aileron is 4°, using a SJA with a maximum outlet velocity of 200m/s and an excitation frequency of 400/2π, the effective lift coefficient generated by the wing is 0.5931. Under the effect of SJA, the control surface efficiency of EPPLER555 wing will be effectively improved. The lift coefficient is reflected by the ratio of the change of lift coefficient after SJA employed to the lift coefficient without synthetic jet actuator.

Experimental study on airfoil flow separation control via an air-supplement plasma synthetic jet

An air-supplement plasma synthetic jet (PSJ) actuator increases the air supplemental volume in the recovery stage and improves the jet energy by attaching a check valve to the chamber of a conventional actuator. To explore the flow control effect and mechanism of the air-supplement actuator, via particle image velocimetry experiments in a low-speed wind tunnel, the flow field and boundary layer characteristics of a two-dimensional airfoil surface under different actuation states were compared for different attack angles and jet orifices. The experimental results show that, compared with the conventional actuation state, the jet energy of the air-supplement PSJ is higher and the indirect mixing effect of the counter-vortex sequence produced by the jet-mainstream interaction is stronger. Furthermore, the boundary layer mixing effect is better, which can further suppress flow separation and improve the critical flow separation attack angle. Moreover, increasing the jet momentum coefficient can enhance the flow control effect. The findings of this study could provide guidance for the flow control application of air-supplement PSJs.

Design of an Acoustic Synthetic Jet Actuator for Flow Control

Synthetic jet technology is widely adopted in active flow control. An actuator with an oscillating diaphragm is a commonly used excitation device for synthetic jet generation. However, it has a disadvantage wherein the volume at the cross-section of the cavity varies unevenly when the diaphragm vibrates, which makes it difficult to use multiple jets corresponding to one diaphragm. In this paper, an acoustic synthetic jet actuator that can generate multiple jets with one diaphragm was designed. The diaphragm vibrated in a cylindrical cavity, transferring air to another constant-volume square cavity through pipes. The square cavity was covered with a multiple-orifice plate for the expulsion and suction of the ambient air. Through this means, the implementation of multiple jets corresponding to one diaphragm was achieved. The multiple jets are called distributed synthetic jets in this paper. Governing parameters that determined the performance of the distributed synthetic jets were given by theoretical derivation. It was found that, under specific geometry conditions, the governing parameters were mainly the frequency and voltage of the input signal to the actuator. Then, the velocity characteristics of the distributed synthetic jets were measured by using a constant-temperature anemometer and the parameter space was determined. The results showed that it was practicable to apply the acoustic actuator to turbulent boundary layer flow control.

Impact of the Soundproofing in the Cavity of the Synthetic Jet Actuator on the Generated Noise

The synthetic jet actuator (SJA) generated high noise which limits the area of its application. In this paper, the five actuators with different types of soundproofing in the cavity were tested and compared to the classic actuator. The resistance and the sound pressure level (SPL) were measured for real power P=1, 2, 4 W, and frequency in a range of 20–150 Hz. The resonant frequency of actuators was designed. Only one type of soundproofing had a significant impact on the resonant frequency. The use of soundproofing in the actuator cavity increased or did not affect the generated noise at a frequency below 120 Hz and only the mineral wool significantly decreased the noise at a frequency above 120 Hz– even 7 dBA. The direction for further investigations was set.

Experimental Study on Characteristics of Plasma Synthetic Jet Actuators With Different Insulating Materials

Plasma synthetic jet actuator (PSJA) has a wide application prospect in the high-speed flow control field for its high jet velocity. In this article, Nylon and Teflon were selected as the insulation materials of synthetic jet actuators to make use of the ionization ablation properties of thermoplastic materials to improve the actuator performance. The performance differences between these actuators and traditional ceramic synthetic jet actuator are obtained. Based on electrical measurement and high-speed schlieren image system, the electrical characteristics and jet performance of the three kinds of actuators at different air pressures are studied. The discharge voltage, current waveform, discharge efficiency, and discharge energy of the three kinds of actuators were almost the same under different pressures. However, Nylon and Teflon materials will be ablated after ionization, resulting in higher jet velocity and longer jet duration time than traditional actuator of ceramic. The ablation of Teflon was most serious. The Teflon actuator had the maximum jet velocity up to 447.51 m/s at 20-kPa pressure. Based on the schlieren image processing method, the affected area of the actuator was calculated. It was found that the maximum affected area of the Teflon actuator was 144.84% larger than that of the ceramic actuator at 100 kPa. The synthetic jet actuator of Teflon had larger affected area and higher jet velocity than other actuators, so it has great application value in high-speed flow field control.

A study on flow control in a hypersonic inlet using a plasma synthetic jet actuator

The plasma synthetic jet actuator (PSJA) has been proven to have potential for shock wave control in the supersonic/hypersonic flow. To evaluate the possibility for the PSJA applied in the hypersonic inlet under a Mach number greater than the design value and provide a deeper understanding of its control mechanism, the relevant two-dimensional numerical simulations are carried out. Based on the discussions about the numerical results, the effects are clear of the actuations generated by the PSJAs, including diffracted waves, synthetic jets, and discharged heat, on the oblique shock waves induced by the compression ramps and the aerodynamic performance of the hypersonic inlet. Concretely, the shapes of the oblique waves are changed by propagations of the diffracted waves, whose starting point moved due to the synthetic jets. A deceleration occurs near the surface of the hypersonic inlet caused by the movement of the discharged heat, leading to a thickener boundary layer. Furthermore, the incremental analysis about the total pressure recovery coefficient at the throat shows that the diffracted waves can increase the static pressure at the throat achieving a higher total pressure recovery coefficient, while the discharged heat makes the total pressure recovery coefficient drop due to a lower local Mach number at the throat. The effect of the discharged heat is more obvious than that of the diffracted waves.

Alleviation of self-support in dual synthetic jet and its self-similarity of streamwise momentum flux

A dual synthetic jet (DSJ) actuator has two chambers sharing the same wall equipped with a single oscillatory diaphragm. The novel structure doubles the function of synthetic jet (SJ) actuator and brings it merits that a traditional synthetic jet actuator does not have like resolving the problems of pressure loading and energy inefficiency. However, self-support, which is unique to DSJ, may result in weak jets or even no jets. In order to effectively solve the self-support problem of DSJ and further improve its performance, this paper proposes a novel DSJ exit structure with a penetrating channel. The experimental and numerical investigations prove that the jet penetration depth and streamwise momentum flux of DSJ are increased by nearly 25%–50%. Furthermore, through the analysis of a large number of simulation data, it is found that the streamwise momentum flux distributions of DSJ under random driving frequency and driving amplitude can be expressed by a unified mathematical fitting formula, that is, the streamwise momentum flux has self-similarity. This criterion can efficiently and quickly calculate the SJ/DSJ driving parameters required for effectively controlling the flow field.

Numerical study of flow separation control over a circular hump using synthetic jet actuators

This study deals with the wall resolved Unsteady Reynolds-Averaged Navier–Stokes (URANS) simulation of boundary layer flow separation over a circular hump model and its active control. An array of Synthetic Jet Actuators (SJAs) is implemented in the hump model to introduce a train of vortex rings into the boundary layer to control flow separation. The OpenFOAM solver is used to numerically simulate and analyze the fluid flow using the k–ω shear stress transport model. Hot wire anemometry and particle image velocimetry measurements are carried out to evaluate the accuracy of the URANS technique as well as the effectiveness of SJAs by comparing numerical predictions to experimental data. The time-averaged results are in a good agreement with experimental results and demonstrate a successful application of SJAs to delay the flow separation by the interactions of vortical structures with the separated shear flow. The three-dimensional simulation also reveals that near wall coherent flow structures (streamwise and spanwise vortices) are responsible for the wall shear stress components. The results can be used to better understand the performance of SJAs and to further improve future actuator configurations.

Influence of mass flux ratio on the evolution of coaxial synthetic jet

This paper highlights a direct numerical simulation study on the flow field of a coaxial synthetic jet (CSJ) generated from two independently controlled synthetic jet actuators, which are combined coaxially with 0° orientation angle. The jet is issued into a quiescent environment from inner and annular openings (orifices) with equal hydraulic diameters, employing an oscillating boundary. Seven different mass flux ratios (Mr) such as 0.25, 0.5, 0.75, 1.0, 1.5, 2.0, and 3.0 are considered for the study. The average velocity (Uavg) of inner jet, measured at orifice exit, is kept at 0.7 m/s (Reynolds number, Re=135), and the same is varied for the annular jet to achieve the desired Mr s. The influence of Mr s on the vortex rings, evolved from inner and annular orifices, along with their dynamics, is predicted by furnishing the instantaneous flow field. Also, we examine the effect of Mr s on the mean flow parameters of the CSJ. Moreover, the CSJ flow field is compared with the inner cavity synthetic jet (SJ), and annular cavity SJ under identical conditions, to demonstrate the superior performance of the CSJ over the single cavity SJs. For CSJ, the azimuthal instability of the evolved vortex rings can be triggered by decreasing the Mr, which results in a wide jet. For Mr≥1.0, the CSJ retains its axisymmetric nature, and the interaction of vortex rings emanating from the inner and annular cavities influences the strength and spreading of the CSJ. The modal decomposition of the instantaneous flow field is also performed using proper orthogonal decomposition method to gain insight of the coherent vortical structures present in the modes. The study will be useful for deploying such novel coaxial synthetic jets in various applications.

Dual Synthetic Jets Actuator and Its Applications—Part II: Novel Fluidic Thrust-Vectoring Method Based on Dual Synthetic Jets Actuator

A novel fluidic thrust-vectoring (FTV) control method based on dual synthetic jets actuator (DSJA) is proposed and evaluated. Numerical simulations are governed by the compressible Unsteady Reynolds-Averaged Navier–Stokes (URANS) equations. According to the results, DSJA is capable of deflecting a primary jet with a velocity of 100 m/s and a height of 50 mm by approximately 18 degrees with a momentum coefficient of 1.96%. It produces comparatively linear control characteristics in almost all deflection angles evaluated (0~23 degrees). The low pressure generated by DSJA, the ejecting enhanced by DSJA, and the co-flow effect produced by the accelerated secondary jet all play roles in the deflection of the primary jet. Since the primary jet is strong enough, the potential of DSJA to provide thrust vector control is revealed.

Effects of loudspeaker-driven synthetic jet actuator parameters on the characteristics of the synthetic jet

In this study, a method for calculating synthetic jet actuator (SJA) parameters by combining diaphragm boundary conditions based on the laws of particle vibration and geometric parameters of the cavity is proposed to obtain accurate rules of variation in which the characteristics of a synthetic jet (SJ) are affected by actuator parameters. Based on the calculating method,an aeroacoustics simulation model of loudspeaker-driven SJA is established with COMSOL software. Simulation results show that the influence of cavity geometry parameters on the velocity characteristics of SJ is greater than that of exciter parameters under the excitation of Helmholtz resonance frequency. Moreover, changing the cavity parameters can increase the jet velocity and reduce the sound pressure level. The velocity characteristics of SJ are consistent with the experimental results.On the basis of the simulation results, the relationship between the aperture length, the cavity length and the modulus of mechanical impedance is established to achieve the maximum jet velocity. It solves various complicated problems of the cavity geometry parameters caused by excitation frequency.

Dual Synthetic Jets Actuator and Its Applications—Part I: PIV Measurements and Comparison to Synthetic Jet Actuator

In order to understand the differences between dual synthetic jets (DSJs) and synthetic jets (SJs), particle image velocimetry (PIV) technology is used to capture the basic flow field characteristics of a dual synthetic jet actuator (DSJA) and a synthetic jet actuator (SJA), and then a careful comparison between them is implemented. The results indicate that a cycle of the DSJ is divided into two stages. In the near-field downstream, a pair of synthetic jets entrain fluid around them and interact with each other, making the flow field complex, and the time-periodic diaphragm dominates them. There is an unfavorable phenomenon of “self-support” between the two jets. In the far-field downstream, the two jets merge into a single, more stable SJ with a higher velocity and a double characteristic frequency. The DSJs have also shown good vectoring characteristics, with the vectoring deflection angle (VDA) changing from about −46° to 46°. The above results demonstrate that the DSJA may replace the traditional SJA in all kinds of applications and extend the applying area of the SJ to more active flow control systems, which cannot be qualified by traditional SJA.

Combined Passive/Active Flow Control of Drag and Lift Forces on a Cylinder in Crossflow Using a Synthetic Jet Actuator and Porous Coatings

This paper combines a synthetic jet actuator (SJA) and a leeward porous coating to alter the aerodynamic forces on a cylinder in crossflow at Re = 4.2 × 104. While SJAs and porous coatings are known to be effective flow control methods in isolation, their combined effect has not been studied. A 2D numerical model was created of a cylinder with a SJA at 90° and 100° leeward porous coating. The model was validated using accompanying water tunnel tests. The combined model was tested for dimensionless frequencies 0.15 <f+< 4 and compared to reference models. For f+< 1, using only the SJA increases the cylinder drag coefficient (Cd). Combining a porous coating with the SJA in that regime lowers the Cd values by 15–21%, and causes an overall reduction in Cd compared to the smooth cylinder baseline case. However, using only the porous coating causes a superior 35% reduction in Cd. For f+> 1, the combined SJA and porous coating configuration did not differ from the SJA only configuration, achieving the largest drag reduction of 45% at f+ = 4. The flow control mechanisms of the SJA and porous coating do not combine constructively in this current setup. However, the porous coating is beneficial for f+< 1, causing an overall drag reduction even when the active SJA tends to increase drag.

Rotor Failure Compensation in a Biplane Quadrotor Based on Virtual Deflection

A biplane quadrotor is a hybrid type of UAV that has wide applications such as payload pickup and delivery, surveillance, etc. This simulation study mainly focuses on handling the total rotor failure, and for that, we propose a control architecture that does not only handle rotor failure but is also able to navigate the biplane quadrotor to a safe place for landing. In this structure, after the detection of total rotor failure, the biplane quadrotor will imitate reallocating control signals and then perform the transition maneuver and switch to the fixed-wing mode; control signals are also reallocated. A synthetic jet actuator (SJA) is used as the redundancy that generates the desired virtual deflection to control the pitch angle, while other states are taken care of by the three rotors. The SJA has parametric nonlinearity, and to handle it, an inverse adaptive compensation scheme is applied and a closed-loop stability analysis is performed based on the Lyapunov method for the pitch subsystem. The effectiveness of the proposed control structure is validated using numerical simulation carried out in the MATLAB Simulink.

Numerical investigation of flow field inner cavity of high-temperature Plasma Synthetic Jet actuator

A Plasma Synthetic Jet (PSJ) actuator is the promised equipment to produce a high-speed synthetic jet, which can be potentially applied to control the supersonic flow. Several researchers paid much attention to its application on Active Flow Control (AFC) in supersonic conditions, but the understanding of the flow field inner the cavity is extremely inadequate. This study aims to use experimental measurement and numerical simulation to reveal the variation of flow field during the issuing PSJ. The PSJ actuator driven by the capacitor group has been designed, and Large Eddy Simulation(LES) was conducted and verified by experimental data with high-resolution particle image velocimetry (PIV) and hot wire anemometer (HWA). The kinetic energy of the PSJ dominantly results from its thermal energy during the stage of plasma deposition, which makes the pressure and temperature of tiny volume near the electrode, increase sharply in microseconds. The electric discharge of the PSJ actuator is simulated by employing the energy input into the source term of the energy equation. The efficiency of the actuator was 20% is demonstrated in this study, which is consistent with the previous research. It is found that the high-pressure zone generated by plasma deposition shifts in a reciprocating way between the bottom and top of the cavity. The pressure inner the cavity and velocity of the PSJ attenuate while oscillating with the real-time. The geometry of the actuator paly a significant role in the performance of the PSJ. Keeping the cavity height constant, the frequency of the pressure is almost the same because the attenuating frequency is related to the cavity height. Increasing cavity height decreases attenuating frequency. The attenuation rate increases with the increase of orifice diameter and decreases of orifice height because of the leaking of gas from the cavity. The mathematic model is built and verified to describe the variation of pressure inner the cavity and the velocity of the PSJ.