Experimental Study on Surface Dielectric Barrier Discharge Plasma Actuator with Different Encapsulated Electrode Widths for Airflow Control at Atmospheric Pressure

The surface dielectric barrier discharge(SDBD) plasma actuator has shown great promise as an aerodynamic flow control device. In this paper, the encapsulated electrode width of a SDBD actuator is changed to study the airflow acceleration behavior. The effects of encapsulated electrode width on the actuator performance are experimentally investigated by measuring the dielectric layer surface potential, time-averaged ionic wind velocity and thrust force. Experimental results show that the airflow velocity and thrust force increase with the encapsulated electrode width. The results can be attributed to the distinct plasma distribution at different encapsulated electrode widths.     

Numerical Simulation of Stall Flow Control Using a DBD Plasma Actuator in Pulse Mode

A numerical simulation method is employed to investigate the effects of the unsteady plasma body force over the stalled NACA 0015 airfoil at low Reynolds number flow conditions.The plasma body force created by a dielectric barrier discharge actuator is modeled with a phenomenological method for plasma simulation coupled with the compressible Navier-Stokes equations.The governing equations are solved using an efficient implicit finitevolume method.The responses of the separated flow field to the effects of an unsteady body force in various interpulses and duty cycles as well as different locations and magnitudes are studied.It is shown that the duty cycle and inter-pulse are key parameters for flow separation control.Additionally,it is concluded that the body force is able to attach the flow and can affect boundary layer grow that Mach number 0.1 and Reynolds number of 45000.     

A saw-tooth plasma actuator for film cooling efficiency enhancement of a shaped hole

This paper reports the large eddy simulations of the effects of a saw-tooth plasma actuator and the laidback fan-shaped hole on the film cooling flow characteristics,and the numerical results are compared with a corresponding standard configuration (cylindrical hole without the sawtooth plasma actuator).For this numerical research,the saw-tooth plasma actuator is installed just downstream of the cooling hole and a phenomenological plasma model is employed to provide the 3D plasma force vectors.The results show that thanks to the downward force and the momentum injection effect of the saw-tooth plasma actuator,the cold jet comes closer to the wall surface and extends further downstream.The saw-tooth plasma actuator also induces a new pair of vortex which weakens the strength of the counter-rotating vortex pair (CRVP) and entrains the coolant towards the wall,and thus the diffusion of the cold jet in the crossflow is suppressed.Furthermore,the laidback fan-shaped hole reduces the vertical jet velocity causing the disappearance of downstream spiral separation node vortices,this compensates for the deficiency of the saw-tooth plasma actuator.Both effects of the laidback fan-shaped hole and the saw-tooth plasma actuator effectively control the development of the CRVP whose size and strength are smaller than those of the anti-counter rotating vortex pair in the far field,thus the centerline and the spanwise-averaged film cooling efficiency are enhanced.The average film cooling efficiency is the biggest in the Fan-Dc =1 case,which is 80％ bigger than that in the Fan-Dc =0 case and 288％ bigger than that in the Cyl-Dc =0 case.     

Numerical and experimental investigation of plasma plume deflection with MHD flow control

This paper presents a composite magneto hydrodynamics(MHD) method to control the lowtemperature micro-ionized plasma flow generated by injecting alkali salt into the combustion gas to realize the thrust vector of an aeroengine.The principle of plasma flow with MHD control is analyzed.The feasibility of plasma jet deflection is investigated using numerical simulation with MHD control by loading the User-Defined Function model.A test rig with plasma flow controlled by MHD is established.An alkali salt compound with a low ionization energy is injected into combustion gas to obtain the low-temperature plasma flow.Finally,plasma plume deflection is obtained in different working conditions.The results demonstrate that plasma plume deflection with MHD control can be realized via numerical simulation.A low-temperature plasma flow can be obtained by injecting an alkali metal salt compound with low ionization energy into a combustion gas at 1800–2500 K.The vector angle of plasma plume deflection increases with the increase of gas temperature and the magnetic field intensity.It is feasible to realize the aim of the thrust vector of aeroengine by using MHD to control plasma flow deflection.     

Experimental Investigation of Hypersonic Flow and Plasma Aerodynamic Actuation Interaction

For hypersonic flow,it was found that the most efective plasma actuator is derived from an electromagnetic perturbation.An experimental study was performed between hypersonic flow and plasma aerodynamic actuation interaction in a hypersonic shock tunnel,in which a Mach number of 7 was reached.The plasma discharging characteristic was acquired in static flows.In a hypersonic flow,the flow field can afect the plasma discharging characteristics.DC discharging without magnetic force is unstable,and the discharge channel cannot be maintained.When there is a magnetic field,the energy consumption of the plasma source is approximately three to four times larger than that without a magnetic field,and at the same time plasma discharge can also afect the hypersonic flow field.Through schlieren pictures and pressure measurement,it was found that plasma discharging could induce shockwaves and change the total pressure and wall pressure of the flow field.     

Experimental investigation on plasma jet deflection with magnetic fluid control based on PIV measurement

This paper is devoted to experimentally investigating the influence of magnetic field intensity and gas temperature on the plasma jet deflection controlled by magneto hydrodynamics. The catalytic ionization seed CS_2CO_3 is injected into combustion gas by artificial forced ionization to obtain plasma fluid on a high-temperature magnetic fluid experimental platform. The plasma jet was deflected under the effect of an external magnetic field, forming a thrust-vector effect.Magnesium oxide was selected as a tracer particle, and a two-dimensional image of the jet flow field was collected using the particle image velocimetry(PIV) measurement method. Through image processing and velocity vector analysis of the flow field, the value of the jet deflection angle was obtained quantitatively to evaluate the thrust-vector effect. The variation of the jet deflection angle with the magnetic field intensity and gas temperature was studied under different experimental conditions. Experimental results show that the jet deflection angle increased gradually with a rise in gas temperature and then increased substantially when the gas temperature exceeded 2300 K. The jet deflection angle also increased with an increase in magnetic induction intensity. Experiments demonstrate it is feasible to use PIV test technology to study the thrust vector under magnetic control conditions.     

Numerical Study of Fluid Dynamics and Heat Transfer Induced by Plasma Discharges

A numerical investigation is conducted to explore the evolution of a plasma discharge and its interaction with the fluid flow based on a self-consistent fluid model which couples the discharge dynamics with the fluid dynamics.The effects of the applied voltage on the distribution of velocity and temperature in initially static air are parainetrically studied.Furthermore,the spatial structure of plasma discharge and the resulting force contours in streamwise and normal directions are discussed in detail.The result shows that the plasma actuator produces a net force that should always be directed away from the exposed electrode,which results in an ionic wind pushing particles into a jet downstream of the actuator.When the energy added by the plasma is taken into account,the ambient air temperature is increased slightly around the electrode,but the velocity is almost not affected.Therefore it is unlikely that the induced flow is buoyancy driven.For the operating voltages considered in this paper,the maximum induced velocity is found to follow a power law,i.e.,it is proportional to the applied voltage to the 3.5 power.This promises an efficient application in the flow control with plasma actuators.     

Electrical and aerodynamic characteristics of sliding discharge based on a microsecond pulsed plasma supply

Plasma flow control technology has broad prospects for application. Compared with conventional dielectric barrier discharge plasma actuators (DBD-PA), the sliding discharge plasma actuator (SD-PA) has the advantages of a large discharge area and a deflectable induced jet. To achieve the basic performance requirements of light weight, low cost, and high reliability required for UAV (Unmanned Aerial Vehicle) plasma flight experiments, this work designed a microsecond pulse plasma supply that can be used for sliding discharge plasma actuators. In this study, the topology of the primary circuit of the microsecond pulse supply is determined, the waveform of the output terminal of the microsecond pulse plasma supply is detected using the Simulink simulation platform, and the design of the actuation voltage, the pulse frequency modulation function and the construction of the hardware circuit are achieved. Using electrical diagnosis and flow field analysis, the actuation characteristics and flow characteristics of sliding discharge plasma under microsecond pulse actuation are studied, the optimal electrical actuation parameters and flow field characteristics are described.     

Numerical study of the flow structures in flat plate and the wall-mounted hump induced by the unsteady DBD plasma

In this work,the dielectric-barrier-discharge plasma actuator was employed to study the flow structures induced by the plasma actuator over a flat plate and a wall-mounted hump.A phenomenological dielectric-barrier-discharge plasma model which regarded the plasma effect as the body force was implemented into the Navier–Stokes equations solved by the method of large eddy simulations.The results show that a series of vortex pairs,which indicated dipole formation and periodicity distribution were generated in the boundary layer when the plasma was applied to the flow over a flat plane.They would enhance the energy exchanged between the near wall region and the free stream.Besides,their spatial trajectories are deeply affected by the actuation strength.When the actuator was engaged in the flow over a wall-mounted hump,the vortex pairs were also produced,which was able to delay flow separation as well as to promote flow reattachment and reduce the generation of a vortex,achieving the goal of reducing dissipation and decreasing flow resistance.     

Analysis of flow separation control using nanosecond-pulse discharge plasma actuators on a flying wing

Abstract Dielectric barrier discharge (DBD) plasma is one of most promising flow control method for its several advantages. The present work investigates the control authority of nanosecond pulse DBD plasma actuators on a flying wing model’s aerodynamic characteristics. The aerodynamic forces and moments are studied by means of experiment and numerical simulation. The numerical simulation results are in good agreement with experiment results. Both results indicate that the NS-DBD plasma actuators have negligible effect on aerodynamic forces and moment at the angles of attack smaller than 16°. However, significant changes can be achieved with actuation when the model’s angle of attack is larger than 16° where the flow separation occurs. The spatial flow field structure results from numerical simulation suggest that the volumetric heat produced by NS-DBD plasma actuator changes the local temperature and density and induces several vortex structures, which strengthen the mixing of the shear layer with the main flow and delay separation or even reattach the separated flow.     

Investigation on Plasma Jet Flow Phenomena During DC Air Arc Motion in Bridge-Type Contacts

Arc plasma jet flow in the air was investigated under a bridge-type contacts in a DC 270 V resistive circuit.We characterized the arc plasma jet flow appearance at different currents by using high-speed photography,and two polished contacts were used to search for the relationship between roughness and plasma jet flow.Then,to make the nature of arc plasma jet flow phenomena clear,a simplified model based on magnetohydrodynamic (MHD) theory was established and calculated.The simulated DC arc plasma was presented with the temperature distribution and the current density distribution.Furthermore,the calculated arc flow vclocity field showed that the circular vortex was an embodiment of the arc plasma jet flow progress.The combined action of volume force and contact surface was the main reason of the arc jet flow.     

Experimental Investigation on Aerodynamic Control of a Wing with Distributed Plasma Actuators

Experimental investigation of active flow control on the aerodynamic performance of a flying wing is conducted.Subsonic wind tunnel tests are performed using a model of a 35°swept flying wing with an nanosecond dielectric barrier discharge(NS-DBD) plasma actuator,which is installed symmetrically on the wing leading edge.The lift and drag coefficient,lift-todrag ratio and pitching moment coefficient are tested by a six-component force balance for a range of angles of attack.The results indicate that a 44.5%increase in the lift coefficient,a 34.2%decrease in the drag coefficient and a 22.4%increase in the maximum lift-to-drag ratio can be achieved as compared with the baseline case.The effects of several actuation parameters are also investigated,and the results show that control efficiency demonstrates a strong dependence on actuation location and frequency.Furthermore,we highlight the use of distributed plasma actuators at the leading edge to enhance the aerodynamic performance,giving insight into the different mechanism of separation control and vortex control,which shows tremendous potential in practical flow control for a broad range of angles of attack.     

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%.     

Experimental Characterization of the Plasma Synthetic Jet Actuator

The plasma synthetic jet is a novel active flow control method because of advantages such as fast response,high frequency and non-moving parts,and it has received more attention recently,especially regarding its application to high-speed flow control.In this paper,the experimental characterization of the plasma synthetic jet actuator is investigated.The actuator consists of a copper anode,a tungsten cathode and a ceramic shell,and with these three parts a cavity can be formed inside the actuator.A pulsed-DC power supply was adopted to generate the arc plasma between the electrodes,through which the gas inside was heated and expanded from the orifice.Discharge parameters such as voltage and current were recorded,respectively,by voltage and current probes.The schlieren system was used for flow visualization,and jet velocities with different discharge parameters were measured.The schlieren images showed that the strength of plasma jets in a series of pulses varies from each other.Through velocity measurement,it is found that at a fixed frequency,the jet velocity hardly increases when the discharge voltage ranges from 16 kV to 20 kV.However,with the discharge voltage fixed,the jet velocity suddenly decreases when the pulse frequency rises above 500 Hz,whereas at other testing frequencies no such decrease was observed.The maximum jet velocity measured in the experiment was up to110 m/s,which is believed to be effective for high-speed flow control.     

Rotor performance enhancement by alternating current dielectric barrier discharge plasma actuation

An experimental system was established to explore the plasma flow control effect for helicopter rotors in hover mode.With the plasma actuator applied at the leading edge of the rotor blades,alternating current dielectric barrier discharge(AC-DBD) plasma actuation was generated by a sinusoidal AC high-voltage generator.By direct force measurement,the influence of actuation parameters on the aerodynamic performance of the rotor was investigated at a tip Reynolds number of 1.7 × 10⁵.AC-D...     

Research on the Peristaltic Flow Acceleration Performance of Asynchronous and Duty Cycle Pulsed DBD Plasma Actuation

Using a plexiglas plate model, the performance of peristaltic flow acceleration in- duced by multiple DBD （dielectric barrier discharge） plasma actuators was studied based on PIV （particle image velocimetry）. The asynchronous and the duty cycle pulsed actuation modes were proposed and tested. The velocity fields induced by multiple DBD plasma actuators with different phase angles and duty cycle ratios were acquired and the momentum transfer characteristics of the flow field were discussed. Consequently, the mechanism of the peristalsis-acceleration multi- ple DBD plasma actuation was analyzed. The results show that the peristaltic flow acceleration effect of multiple plasma actuators occurs mainly in paraelectric direction, and the mechanism of peristaltic flow acceleration is ejection pushing effect rather than injection pumping effect. The asynchronous and the duty cycle pulsed actuation modes can, with energy consumption increase of merely 10%, achieve 65% and 42% increase of downstream velocity, and thus are promising in velocity improvement and energy saving.     

Reduction of turbulent boundary layer drag through dielectric-barrier-discharge plasma actuation based on the Spalding formula

Abstract It is a very difficult task to develop a method of reducing turbulent boundary layer drag. However, in recent years, plasma flow control technology has demonstrated huge potential in friction drag reduction. To further investigate this issue, a smooth plate model was designed as a testing object arranged with a bidirectional dielectric-barrier-discharge (DBD) plasma actuator. In addition, measurement of skin friction drag was achieved by applying hot wire anemometry to obtain the velocity distribution of the turbulent boundary layer. A method of quantifying the friction drag effect was adopted based on the Spalding formula fitted with the experiment data. When plasma actuation was conducted, a velocity defect occurred at the two measuring positions, compared with the no plasma control condition; this means that the DBD plasma actuation could reduce the drag successfully in the downstream of the actuator. Moreover, drag reduction caused by backward actuation was slightly more efficient than that caused by forward actuation. With an increasing distance from plasma actuation, the drag-reduction effect could become weaker. Experimental results also show that the improvement of drag-reduction efficiency using a DBD plasma actuator can achieve about 8.78% in the local region of the experimental flat model.     

Functions of intrinsic magnetic field line structures on lithium ion transport in the LHD plasma periphery

Plasma discharge operation with lithium coating suggests that the lithium effectively control neutral particles in the plasma periphery, which can lead to improvement of plasma parameters. The effect of lithium coating on the large helical device (LHD) for a closed helical divertor configuration is discussed from viewpoints of neutral particle and impurity ion transport in the plasma periphery. It shows that the closed helical divertor configuration can enhance the neutral particle density in the divertor region, which is enough to achieve efficient particle control, and that it can effectively confine neutral lithium atoms near divertor plates. A one-dimensional impurity (lithium) ion transport analysis along magnetic field lines on divertor legs indicates that the friction force due to the plasma flow from the main plasma is dominant over the thermal force caused by the temperature gradient on the divertor legs, which prevents lithium ion contamination in the main plasma and excessive cooling of the plasma temperature in an ergodic layer. The analysis shows that the lithium coating is compatible with LHD plasma discharge operation for the closed helical divertor configuration.     

An improved mechanistic critical heat flux model and its application to motion conditions

The motion of the flow channel will create a new acceleration field other than gravitational acceleration field for the fluid flow in the heated channel. And the new acceleration field will create new forces acting on bubbles, which will make the intermittent vapor blankets and bubbles in the near-wall region behave in a different way. In order to investigate the influence of this new arisen acceleration field on the occurrence of critical heat flux (CHF), an improved model based on microscopic mechanism of bubble dynamics is developed with the liquid sublayer dryout mechanism which has been well investigated by the previous researchers. Forces exerted on the vapor blankets have been taken into account to determine the liquid sublayer thicknesses and relative velocities of the vapor blankets through force balances in the radial direction and axial direction, respectively. At the same time, the proposed liquid sublayer dryout model presents pretty good prediction ability for saturated flow boiling CHF. The parametric trends of CHF in terms of mass flow rate, inlet subcooling and pressure for both the subcooled and saturated flow boiling are studied qualitatively and quantitatively. The effects of accelerations induced by channel motions in both the flow direction and the normal direction to the heated wall are investigated. Comparisons between the prediction results and the experimental data show good precision and accuracy.     

Active control of noise amplification in the flow over a square leading-edge flat plate utilizing DBD plasma actuator

Perturbation is generally considered as the flow noise,and its energy can gain transient growth in the separation bubble.The amplified perturbations may cause unstable Kelvin–Helmohltz vortices which induce the three-dimensional transition.Active control of noise amplification via dielectric barrier discharge plasma actuator in the flow over a square leading-edge flat plate is numerically studied.The actuator is installed near the plate leading-edge where the separation bubble is formed.The maximum energy amplification of perturbations is positively correlated with the separation bubble scale which decreases with the increasing control parameters.As the magnitude of noise amplification is reduced,the laminar-turbulent transition is successfully suppressed.