Plasma Synthetic Jet Actuator Research Articles

Breaking the limitation of thermodynamic cycle efficiency of the plasma synthetic jet actuator: Noble gases

The low thermodynamic cycle efficiency of the plasma synthetic jet actuator (PSJA) limits its application in flow control of supersonic aircraft. To improve the thermodynamic cycle efficiency of the PSJA, the energy conversion process of the PSJA under single discharge has been investigated by thermodynamic theory analysis and numerical simulation. The relations between thermodynamic cycle efficiency, specific heat ratio of gas medium, non-dimensional energy deposition and heating efficiency are established by theoretical deduction. Employing the three-dimensional nonconstant electrode center energy deposition model, energy conversion processes in the PSJA with six different gas mediums have been investigated. The simulation results show that the thermodynamic cycle efficiency of the PSJA with noble gas medium can exceed 3.2 %, which is 1.92 times of the PSJA with air medium due to their low volume specific heat. The maximum jet x-velocity of helium can reach 493.11 m/s, which is 3.3 times higher than that of air. Consequently, noble gases prove to be effective in improving the thermodynamic cycle efficiency of the PSJA and enhancing the strength of the synthetic jet. The advancement in the performance of the PSJA contributes to their enhanced capabilities in the field of active flow control.

Experimental study on shock interaction control of double wedge in high-enthalpy hypersonic flow subject to plasma synthetic jet

The hypersonic shock-shock interaction flow field at double-wedge geometries controlled by plasma synthetic jet actuator is experimentally studied in a Ma = 8 high-enthalpy shock tunnel with the purpose of exploring a novel technique for reducing surface heat flux in a real flight environment. The results demonstrate that increasing the discharge energy is advantageous in eliminating the shock wave, shifting the shock wave interaction point, and shortening the control response time. The oblique shock wave can be completely removed when the actuator's discharge energy grows from 0.4 J to 11.5 J, and the displacement of the shock wave interaction point increases by 124.56%, while the controlled response time is shortened by 30 μs. Besides, the reduction in diameter of the jet exit is firstly proved to have a negative impact on energy deposition in a working environment with incoming flow, which reduces the discharge energy and hence decreases the control effect. The shock wave control response time lengthens when the jet exits away from the second wedge. Along with comparing the change in wall heat flux at the second wedge over time, the control effect of plasma synthetic jet actuator with and without inflation is also analyzed. When plasma synthetic jet works in inflatable mode, both the ability to eliminate shock waves and the shifting effect of the shock wave interaction point are increased significantly, and the wall heat flux is also reduced.

Plasma synthetic jet actuator array driven by a programmable triggered Marx high-voltage generator

A plasma synthetic jet (PSJ) actuator array driven by a self-triggered Marx high-voltage generator can simultaneously actuate multichannel PSJ actuators to form jet arrays; however, the discharge frequency cannot be controlled by programmable electrical signals. To address this, programmable high-voltage pulses are used to trigger a Marx high-voltage generator and regulate the discharge frequency of the PSJ actuator array. The electrode gap range for achieving a programmable triggered discharge is determined, and typical discharge images and basic discharge characteristics are obtained. The effects of trigger frequency and voltage amplitude on the discharge frequency are studied. The high-speed Schlieren technique is used to obtain flow-field characteristics of five-channel PSJ actuators under a programmable triggered state. The programmable triggered Marx high-voltage generator can achieve programmable control of the discharge frequency with an approximate linear control range of 10–30 Hz and a nonlinear saturation range of 30–100 Hz. In the approximate linear control range, the discharge frequency increases almost linearly with trigger frequency under different trigger voltage amplitudes. One of the channels of the five-channel synthetic jet actuators achieves the highest jet height and speed of 70 m/s, while those of the others are similar but slightly lower. There is no significant decrease in the jet height or speed of the five-channel PSJ actuators with the increase in the trigger frequency, which is beneficial for flow-control applications.

Experimental investigation on periodic characteristics of high-frequency oblique slot plasma synthetic jet actuator

A plasma synthetic jet actuator with a high-frequency oblique slot was designed for supersonic flow control. The actuator's periodic operation characteristics were investigated using electrical parameter measurements and high-speed schlieren techniques. Experimental findings indicate that the actuator can stably operate within the frequency range of 0–2400 Hz. With increasing operating frequency, the breakdown voltage, maximum current, and discharge energy decrease, while the energy efficiency of the discharge increases. Moreover, the experiment revealed for the first time that an increase in the number of charged particles within the cavity leads to a decrease in breakdown voltage, and the concentration of charged particles reaches saturation at approximately 1200 Hz. High-speed schlieren observations indicate substantial inter-cycle influences in the periodic jet. At higher operating frequencies, the impact of inter-cycle flow field effects becomes more pronounced. The oblique slot plasma synthetic jet exhibits clear directionality in the distribution of shock waves and jet. The oblique slot jet also shows a significant wall attachment effect. These characteristics are beneficial for enhancing the flow control capability of the actuator. At 1200 Hz, the actuator achieves a discharge efficiency of 63% and a maximum jet front velocity of 309 m/s, showcasing its superior overall performance.

Experimental characterization of a modified high-speed plasma synthetic jet actuator with oblique-slot exit

In the field of flow control research, oblique jets are known to offer several advantages over vertical jets. To gain a comprehensive insight into the flow field characteristics of a plasma synthetic jet actuator with an oblique-slot exit, the related experiments are conducted. The experiment employed high-speed schlieren imaging techniques and electrical parameter measurements to acquire the flow field characteristics and discharge properties of the oblique-slot actuator, followed by a comparative analysis with a vertical circular orifice actuator. The oblique-slot plasma synthetic jet exhibits a wall-attaching effect and asymmetric flow characteristics, which differ from those of the vertical circular orifice actuator. The actuator generates a wall jet with an initial velocity of 389.5 ± 15.08 m/s, effectively propelling the fluid within the boundary layer. The Mach number of the precursor shock wave in the direction of the jet reaches 1.59, but decreases to just 1.02 in the opposite direction. Over a period in the range of 10–70 μs, the Froude number of the plasma jet decreases from 1841 to 238. The dominant role of the inertial force gradually weakens, while the influence of buoyancy increases, causing the jet boundary to move upward. The oblique-slot jet configuration represents a typical planar jet, exhibiting superior flow control uniformity compared with the vertical circular orifice jet. The results indicate that the high-speed oblique-slot plasma synthetic jet actuator designed in this study possesses distinct advantages over vertical circular orifice actuators for high-speed fluid flow control.

Effects of different working parameters on the turbulent drag reduction regulated by annular plasma synthetic jet actuators

Reduction of turbulent drag force is one of important works in the design of airplanes and hypersonic aircrafts. The annular plasma synthetic jet (APSJ) has become an interesting and popular flow control method in reducing the drag of turbulent boundary layers. In this paper, a comprehensive experimental study is carried out on the turbulent drag reduction regulated by an array of annular plasma synthetic jet actuators. The effects of the operating parameters such as the actuation voltage, the pulse frequency and the incoming wind speed on the drag reduction rate are studied and discussed in detail. The performances of the plasma actuator array are evaluated and summarized at multiple working conditions. Finally, the coherent structures of turbulence and the hairpin-like vortices are depicted and discussed. The results show that the optimal drag reduction rate is achieved, as the actuation voltage, pulse frequency and incoming wind speed are Vpp = 7 kV, fp= 50 Hz, and U∞ = 7 m/s, respectively. A resonant coupling phenomenon is observed when the pulse frequency of the actuators approaches the characteristic frequency of the coherent structure. The upward sweep flow induced by APSJ actuators may lead to a reduction of the turbulent drag force, but the downward wash flow leads to an increase in the drag. Present study could provide solid experimental data and a helpful guidance for the drag reduction of an airplane.

Investigation of drag reduction mechanism for blunt bodies with plasma spikes

The two main problems in hypersonic vehicles are wave drag and aerodynamic heating. This work proposes a novel method for drag reduction by combining spikes with the plasma synthetic jet actuator (PSJA). Numerical simulations are performed to better understand the drag reduction mechanism with an incoming flow at Mach 6. The results suggest that the flow field is affected primarily by the diffracted wave and synthetic jet. The maximum drag reduction reaches 47.7% with the plasma spike compared with the opposing jet. A better drag reduction effect is achieved when increasing the energy density of the PSJA, while the propagation velocity of the diffracted wave remains constant. A wider and faster jet is obtained with a larger PSJA orifice diameter. However, the control time of the jet shortens. A mode conversion occurs when the orifice diameter is 1 mm. Furthermore, the maximum drag reduction rate increases from 37.6% to 49.0% when the length diameter ratio (L/D) increases from 0.5 to 1.5. The effect of spike length on drag reduction decreases gradually at greater lengths.

Internal Characteristics of Air-Supplied Plasma Synthetic Jet Actuator

Conventional plasma synthetic jet actuators rely only on jet orifice for suction when functioning for long durations. A limited supplementary gas leads to jet velocity reduction and weakening of the flow control ability. Therefore, this study proposes an air-supplied actuator with a check valve externally connected to the cavity to improve its gas-supplying ability and jet performance. A quartz glass discharge chamber is developed to clarify the internal working mechanism of the air-supplied actuator. High-speed schlieren is employed to photograph the internal flow field of the discharge chamber. The results reveal that the inhalation airflow velocity of the jet orifice is doubled when the actuator is continuously working in the effective frequency band under the combined action of additional air supply from the check valve in the inhalation recovery stage. The gas pressure in the cavity is closer to the initial discharge state, discharge breakdown voltage is higher, discharge energy is stronger, and the process of gas expansion to generate a jet is less affected by the core defect of the heat source, thereby significantly increasing the jet velocity and saturation operating frequency of the actuator. The obtained results have important implications for the performance optimization of the air-supplied actuator.

Experimental investigation on de-icing by an array of impact rod-type plasma synthetic jets

Since flight accidents due to aircraft icing occur from time to time, this paper proposes an array of impact rod-type plasma synthetic jet de-icing methods for aircraft icing problems. The impact rod-type plasma synthetic jet actuator (PSJA) is based on the traditional PSJA with an additional impact rod structure for better de-icing in the flight environment. In this work, we first optimize the ice-breaking performance of a single-impact rod-type PSJA, and then conduct an array of impact rod-type plasma synthetic jet ice-breaking experiments to investigate the relationship between crack expansion and discharge energy, ice thickness and group spacing. The results show that the impact force and impulse of a single-impact rod-type PSJA are proportional to the discharge energy, and there exists a threshold energy Q min for a single actuator to break the ice, which is proportional to the ice thickness. Only when the discharge energy reaches above Q min can the ice layer produce cracks, and at the same time, the maximum radial crack length produced during the ice-breaking process is proportional to the discharge energy. When the ice is broken by an array of impact rod PSJAs, the discharge energy and group spacing together determine whether the crack can be extended to the middle region of the actuator. When the group spacing is certain, increasing the energy can increase the intersection of cracks in the middle region, and the ice-fragmentation degree is increased and the ice-breaking effect is better. At the same time, the energy estimation method of ice breaking by an array of impact rod-type PSJAs is proposed according to the law when a single actuator is breaking ice.

Experimental and numerical investigation of a self-supplementing dual-cavity plasma synthetic jet actuator

The primary issue regarding the plasma synthetic jet actuator (PSJA) is its performance attenuation at high frequencies. To solve this issue, a self-supplementing, dual-cavity, plasma synthetic jet actuator (SD-PSJA) is designed, and the static properties of the SD-PSJA are investigated through experiments and numerical simulations. The pressure measurement shows that the SD-PSJA has two saturation frequencies (1200 Hz and 2100 Hz), and the experimental results show that both the saturation frequencies decrease as the volume of the bottom cavity of the SD-PSJA increases. As the size of the supplement hole increases, the first saturation frequency increases continuously, while the second saturation frequency shows a trend of first decreasing and then increasing. Numerical simulations show that the working process of the SD-PSJA is similar to that of the PSJA, but the volume of the cavity in the SD-PSJA is smaller than that of the PSJA; the SD-PSJA can supplement air to the top cavity through two holes, thus reducing the refresh time and effectively improving the jet intensity of the actuator at high frequencies.

Quantification of Aerodynamic Effects of PSJA on Small UAV in Flat Turn with Side Force Fin

Indoor flight experiment is conducted to verify the effectiveness of plasma synthetic jet actuator (PSJA) in improving aerodynamic characteristics of small unmanned aerial vehicle (UAV). It is required to realize small radius of turn that enables indoor experiment and low speed where the actuator exhibits high efficiency. Such requirements are satisfied by flat turn with side force fin, the vertical wing to produce a centripetal force. The effect of lift enhancement is quantified by the increase in aileron deflection caused by operation of PSJA on the outside wing. The results of flight simulations based on force measurement experiment for an airfoil model also support the validity of the proposed method.

Plasma kernel model and energy transformation characteristic of plasma synthetic jet actuator

This article conducted a theoretical, experimental, and numerical investigation to clarify the plasma kernel model and energy transformation characteristics of the plasma synthetic jet actuator (PSJA). Plasma kernel and blast wave theory were used to describe the formation and evolution of the arc-discharge energy deposition process and build a plasma kernel model. Schlieren experiment visualized the formation and evolution of the synthetic jet flow and used it as a validation of the numerical simulation. Five plasma synthetic jet actuators with different cavity volumes (128–512 mm3) and different discharge energy (2.8–11.3 mJ) were modeled numerically to investigate the energy transformation characteristic of PSJA. Results showed that plasma kernel radius and formation time could be theoretically predicted with specific deposition energy and correspond well with simulation results. The peak pressure and temperature rise in the cavity can also be calculated. Moreover, the proportion of kinetic energy increases linearly with non-dimensional deposition energy, while potential energy has a reverse tendency with non-dimensional cavity volume and deposition energy.

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.

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.

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.

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.

Study on propagation mechanisms of the actuations generated by plasma synthetic jet actuator in a supersonic flow

The plasma synthetic jet actuator (PSJA) has a potential application in the flow control, especially for the supersonic and hypersonic flow. In order to make a deeper understanding on the propagation processes of the actuation generated by the PSJA in a supersonic flow, both the schlieren experiment and the numerical simulation are adopted for the analyses. Based on the analytic geometry method, the propagation of the diffracted wave, the synthetic jet and the dis-charged heat are discussed in detail. The effects of the mainstream Mach number and the discharge strength on the propagation processes are also deeply analyzed. Besides, an analytic model and relevant motion equations are established for the forecast of the actuations. The results suggest that the 1st diffracted wave expands around and propagates along the mainstream direction. The synthetic jet will change the start point of the oblique wave. Further, the propagation of the dis-charged heat is also related to the mainstream.

Control of flow separation over a wing model with plasma synthetic jets

An array of 30 plasma synthetic jet actuators (PSJAs) is deployed using a modified multichannel discharge circuit to suppress the flow separation over a straight-wing model. The lift and drag of the wing model are measured by a force balance, and the velocity fields over the suction surface are captured by a particle imaging velocimetry system. Results show that the flow separation of the straight wing originates from the middle of the model and expands towards the wingtips as the angle of attack increases. The flow separation can be suppressed effectively by the PSJAs array. The best flow control effect is achieved at a dimensionless discharge frequency of F + = 1, with the peak lift coefficient increased by 10.5% and the stall angle postponed by 2°. To further optimize the power consumption of the PSJAs, the influence of the density of PSJAs on the flow control effect is investigated. A threshold of the density exits (with the spanwise spacing of PSJAs being 0.2 times of the chord length in the current research), below which the flow control effect starts to deteriorate remarkably. In addition, for comparison purposes, a dielectric barrier discharge (DBD) plasma actuator is installed at the same location of the PSJAs. At the same power consumption, 4.9% increase of the peak lift coefficient is achieved by DBD, while that achieved by PSJAs reaches 5.6%.

A novel three-dimensional center energy deposition model for the hybrid synthetic jet actuator

The low energy conversion efficiency of the plasma synthetic jet actuator (PSJA) and the misfiring problem caused by the low gas backfill rate have hindered the application of the PSJA in supersonic aircraft for fast response aerodynamic control. Although the hybrid synthetic jet actuator (HSJA) based on the PSJA has the potential to solve these problems, the heat and mass transfer mechanism of hybrid synthetic jets is still unclear. According to the capacitive discharge process, a novel three-dimensional center energy deposition model was proposed in this paper. The accuracy of the three-dimensional center energy deposition model was verified by comparing it with the experimental results. Considering the damped oscillation of the discharge intensity, the effect of nonconstant center energy deposition on the heat and mass transfer inside the cavity was further discussed. The simulation results show that the electrodes have an impact on the creation and evolution of the vortices inside the cavity. And the three-dimensional nonconstant center energy deposition model reveals the real heat and mass transfer mechanism of the HSJA, which provides the theoretical foundation for improving energy conversion efficiency and gas backfill rate of the HSJA.

Experimental and numerical investigation on opposing plasma synthetic jet for drag reduction

Experimental and numerical studies are carried out to validate the potential of opposing Plasma Synthetic Jet (PSJ) for drag reduction for a hemisphere. Firstly, flow field changes of opposing PSJ are analyzed by comparing the experimental schlieren images and simulation results in a supersonic free stream of Mach number 3. As PSJ is a kind of unsteady pulsed jet, the shock standoff distance increases initially and then decreases under the control of PSJ, which corresponds to the change of the strength of PSJ. Accordingly, the amount of drag reduction of the hemisphere increases initially and then decreases. It is found that there is a short period of “drag rise” during the formation of PSJ before the drag reduction, which is induced by the generation of normal shock waves and the area difference of the cavity wall of PSJ Actuator (PSJA). Secondly, the effects of five parameters, including exit diameter, discharge energy of PSJA, Mach number, static pressure of incoming flow and angle of attack, on drag reduction of opposing PSJ were studied in detail by using numerical method. It is found that the Maximum Pressure Ratio (MPR) has a significant impact on the average drag reduction for a configuration-determined PSJA. For the configuration selected in this study, the flow field of opposing PSJ shows typical Short Penetration Mode (SPM) in a control cycle of PSJ when the MPR is less than 0.89. However, the flow field shows typical Long Penetration Mode (LPM) at some time when the MPR is bigger than 0.89. Relatively better drag reduction is achieved in this case.