Experimental investigation of dynamic stall flow control using a microsecond-pulsed plasma actuator

To alleviate the performance deterioration caused by dynamic stall of a wind turbine airfoil,the flow control by a microsecond-pulsed dielectric barrier discharge(MP-DBD) actuator on the dynamic stall of a periodically pitching NACA0012 airfoil was investigated experimentally.Unsteady pressure measurements with high temporal accuracy were employed in this study,and the unsteady characteristics of the boundary layer were investigated by wavelet packet analysis and the moving root mean square method based on the acquired pressure.The experimental Mach number was 0.2,and the chord-based Reynolds number was 870 000.The dimensionless actuation frequencies F+ were chosen to be 0.5,1,2,and 3,respectively.For the light dynamic regime,the MP-DBD plasma actuator plays the role of suppressing flow separation from the trial edge and accelerating the flow reattachment due to the high-momentum freestream flow being entrained into the boundary layer.Meanwhile,actuation effects were promoted with the increasing dimensionless actuation frequency F+.The control effects of the deep dynamic stall were to delay the onset and reduce the strength of the dynamic stall vortex due to the accumulating vorticity near the leading edge being removed by the induced coherent vortex structures.The laminar fluctuation and Kelvin-Helmholtz(K-H) instabilities of transition and relaminarization were also mitigated by the MP-DBD actuation,and the alleviated K-H rolls led to the delay of the transition onset and earlier laminar reattachment,which improved the hysteresis effect of the dynamic stall.For the controlled cases of F+=2,and F+=3,the laminar fluctuation was replaced by relatively low frequency band disturbances corresponding to the harmonic responses of the MP-DBD actuation frequency.

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 inter- pulses 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.

Flow control performance evaluation of a tri-electrode sliding discharge plasma actuator

Tri-electrode sliding discharge(TED)plasma actuators are formed by adding a direct current(DC)exposed electrode to conventional dielectric barrier discharge(DBD)plasma actuators.There are three TED modes depending on the polarity and amplitude of the DC supply:DBD discharge,extended discharge and sliding discharge.This paper evaluates the electrical,aerodynamic and mechanical characteristics of a TED plasma actuator based on energy analysis,particle image velocimetry experiments and calculations using the Navier-Stokes equation.The flow control performances of different discharge modes are quantitatively analyzed based on characteristic parameters.The results show that flow control performance in both extended discharge and sliding discharge is more significant than that of DBD,mainly because of the significantly higher(up to 141%)body force of TED compared with DBD.However,conductivity loss is the primary power loss caused by the DC polarity for TED discharge.Therefore,power consumption can be reduced by optimizing the dielectric material and thickness,thus improving the flow control performance of plasma actuators.

Airfoil friction drag reduction based on grid-type and super-dense array plasma actuators

To improve the cruise flight performance of aircraft, two new configurations of plasma actuators(grid-type and super-dense array) were investigated to reduce the turbulent skin friction drag of a low-speed airfoil. The induced jet characteristics of the two actuators in quiescent air were diagnosed with high-speed particle image velocimetry(PIV), and their drag reduction efficiencies were examined under different operating conditions in a wind tunnel. The results showed that the grid-type plasma actuator was capable of producing a wall-normal jet array(peak magnitude: 1.07 m/s) similar to that generated in a micro-blowing technique, while the superdense array plasma actuator created a wavy wall-parallel jet(magnitude: 0.94 m/s) due to the discrete spanwise electrostatic forces. Under a comparable electrical power consumption level,the super-dense array plasma actuator array significantly outperformed the grid-type configuration,reducing the total airfoil friction drag by approximately 22% at a free-stream velocity of 20 m/s.The magnitude of drag reduction was proportional to the dimensionless jet velocity ratio(r), and a threshold r = 0.014 existed under which little impact on airfoil drag could be discerned.

Flow separation control over an airfoil using continuous alternating current plasma actuator

The flow separation control over an NACA 0015 airfoil using continuous alternating current(AC)dielectric barrier discharge(DBD)plasma actuator is investigated experimentally and numerically.This work is intended to report some observations made from our experiment,to which little attention is paid in the previous studies,but which is thought to be important to the understanding of control of complex flow separation with AC DBD.To this end,the response of separated flow to AC plasma actuation is visualized through the time-resolved particle image velocimetry(PIV)measurement,whereas numerical simulation is carried out to complement the experiment.The flow control process at chord-based Reynolds number(Re)of 3.31×105 is investigated.It is found that the response of external flow to plasma forcing is delayed for up to tens of milliseconds and the delay time increases with angle of attack increasing.Also observed is that at the intermediate angle of attack near stall,the forced flow features a well re-organized flow pattern.However,for airfoil at high post-stall angle of attack,the already well suppressed flow field can recover to the massively separated flow state and then reattach to airfoil surface with the flow pattern fluctuating between the two states in an irregular manner.This is contrary to one’s first thought that the forced flow at any angles of attack will become well organized and regular,and reflects the complexity of flow separation control.

Plasma Virtual Actuators for Flow Control

Dielectric-barrier-discharge (DBD) plasma actuators are all-electric devices with no moving parts. They are made of a simple construction, consisting only of a pair of electrodes sandwiching a dielectric sheet. When AC voltage is applied, air surrounding the upper electrode is ionized, which is attracted towards the charged dielectric surface to form a wall jet. Control of flow over land and air vehicles as well as rotational machinery can be carried out using this jet flow on demand. Here we review recent developments in plasma virtual actuators for flow control that can replace conventional actuators for better aerodynamic performance.

Vortex dynamics over an airfoil controlled by a nanosecond pulse discharge plasma actuator at low wind speed

The vortex dynamics of flow over an airfoil controlled by a nanosecond pulse dielectric-barrierdischarge(NS-DBD) actuator is studied at a Reynolds number of 1×10^5 through wind tunnel experiments and numerical simulation. The numerical method is validated through comparison of the simulated and measured results regarding the effect of the discharge of an NS-DBD actuator placed on a flat plate. The simulated results show that vorticity is mainly induced by the baroclinic torque after plasma discharge, i.e. the term(1/p^2▽p×▽p) in the equation of vorticity evolution. Both experimental and simulated results demonstrate that after the discharge of the NS-DBD actuator a series of vortices are developed in the shear layer and pull the high-moment fluid down to the wall, enhancing the mixing of internal and external flows.

Experimental study on surface arc plasma actuation-based hypersonic boundary layer transition flow control

Effective control of hypersonic transition is essential.In order to avoid affecting the structural proflle of the aircraft,as well as reducing power consumption and electromagnetic interference,a low-frequency surface arc plasma disturbance experiment to promote hypersonic transition was carried out in theΦ0.25 m double-throat Ludwieg tube wind tunnel at Huazhong University of Science and Technology.Contacting printed circuit board sensors and non-contact focused laser differential interferometry testing technology were used in combination.Experimental results showed that the low-frequency surface arc plasma actuation had obvious stimulation effects on the second-mode unstable wave and could promote boundary layer transition by changing the spectral characteristics of the second-mode unstable wave.At the same time,the plasma actuation could promote energy exchange between the second-mode unstable wave and other unstable waves.Finally,the corresponding control mechanism is discussed.

Leading-edge flow separation control over an airfoil using a symmetrical dielectric barrier discharge plasma actuator

In order to promote an in-depth understanding of the mechanism of leading-edge flow separation control over an airfoil using a symmetrical Dielectric Barrier Discharge(DBD) plasma actuator excited by a steady-mode excitation, an experimental investigation of an SC(2)-0714 supercritical airfoil with a symmetrical DBD plasma actuator was performed in a closed chamber and a low-speed wind tunnel. The plasma actuator was mounted at the leading edge of the airfoil.Time-resolved Particle Image Velocimetry(PIV) results of the near-wall region in quiescent air suggested that the symmetrical DBD plasma actuator could induce some coherent structures in the separated shear layer, and these structures were linked to a dominant frequency of f0= 39 Hz when the peak-to-peak voltage of the plasma actuator was 9.8 kV. In addition, an analysis of flow structures without and with plasma actuation around the upper side of the airfoil at an angle of attack of18° for a wind speed of 3 m/s(Reynolds number Re = 20000) indicated that the dynamic process of leading-edge flow separation control over an airfoil could be divided into three stages. Initially, this plasma actuator could reinforce the shedding vortices in the separated shear layer. Then, these vortical structures could deflect the separated flow towards the wall by promoting the mixing between the outside flow with a high kinetic energy and the flow near the surface. After that, the plasma actuator induced a series of rolling vortices in the vicinity of the suction side of the airfoil, and these vortical structures could transfer momentum from the leading edge of the airfoil to the separated region, resulting in a reattachment of the separated flow around the airfoil.

Turbulent boundary layer separation control using plasma actuator at Reynolds number 2000000

An experimental investigation was conducted to evaluate the effect of symmetrical plasma actuators on turbulent boundary layer separation control at high Reynolds number. Compared with the traditional control method of plasma actuator, the whole test model was made of aluminum and acted as a covered electrode of the symmetrical plasma actuator. The experimental study of plasma actuators＇ effect on surrounding air, a canonical zero-pressure gradient turbulent boundary, was carried out using particle image velocimetry （PIV） and laser Doppler velocimetry （LDV） in the 0.75 m × 0.75 m low speed wind tunnel to reveal the symmetrical plasma actuator characterization in an external flow. A half model of wing-body configuration was experimentally investigated in the 3.2 m low speed wind tunnel with a six-component strain gauge balance and PIV. The results show that the turbulent boundary layer separation of wing can be obviously suppressed and the maximum lift coefficient is improved at high Reynolds number with the symmetrical plasma actuator. It turns out that the maximum lift coefficient increased by approximately 8.98% and the stall angle of attack was delayed by approximately 2° at Reynolds number 2 ×10……6. The effective mechanism for the turbulent separation control by the symmetrical plasma actuators is to induce the vortex near the wing surface which could create the relatively large- scale disturbance and promote momentum mixing between low speed flow and main flow regions.

Experimental Study of Rotor Flow Separation Control using a New Type of Dielectric Barrier Discharge Plasma Actuator

Flow separation occurring on rotor blades is an important limiting factor for helicopter performance. This paper presents a new type of dielectric barrier discharge(DBD) plasma actuator for rotor blade flow separation control called bipolar DBD plasma actuator. The bipolar DBD plasma actuator's connection mode differs from traditional plasma actuators and eliminates reverse discharge between electrodes. The experiments in this work were carried out by smoke-wire flow visualization and PIV technology in the open test section of a low speed wind tunnel, and solved the problem of high voltage electricity supplied to the plasma actuator while the rotor rotated. In this experiment, the rotor, camera, and laser were synchronized to obtain results. Smoke-wire results and PIV results illustrated that the flow separation weakened with increasing rotor speed; the separated flow area was large at a rotating speed of 300 r/min and gradually became smaller at the rotating speed of 600 r/min, the flow separation disappeared at the rotating speed of 1200 r/min. When the plasma was active, both smoke-wire results and PIV results showed the flow separation area was greatly reduced at the rotating speed of 300 r/min and disappeared at the rotating speeds of 600 r/min and 1200 r/min, the rotor flow separation at high angles of attack could be effectively controlled by the new DBD plasma actuator.

Recent developments in thermal characteristics of surface dielectric barrier discharge plasma actuators driven by sinusoidal high-voltage power

Flow control using surface Dielectric Barrier Discharge(DBD)plasma actuators driven by a sinusoidal alternating-current power supply has gained significant attention from the aeronautic industry.The induced flow field of the plasma actuator,with the starting vortex in the wall jet,plays an important role in flow control.However,the energy consumed for producing the induced flow field is only a small fraction of the total energy utilized by the plasma actuator,and most of the total energy is used in gas heating and dielectric heating.Therefore,an in-depth analysis of the thermal characteristics of the plasma actuator is the key to develop its potential capability further.In addition,compared with the investigation on the aerodynamic characteristics of the plasma actuator,there is a relative lack of detail in the study of its thermal characteristics.Understanding the thermal characteristics of the plasma actuator is of great interest for providing a deeper insight into the underlying working principles,advancing its numerical simulation model,prolonging its life,and achieving several potential engineering applications,such as antiicing and deicing.The present paper reviews the thermal characteristics of the plasma actuator,summarizes the influence of the dielectric film and actuation parameters on heating,and discusses the formation and transfer mechanism of the induced heating based on the discharge regimes of the plasma actuator in one cycle.

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.

Flow Control over a Conical Forebody by Periodic Pulsed Plasma Actuation

The flow control mechanism of plasma actuators with periodic pulsed discharge to control the bi-stable vortices over a cone-cylinder is investigated. The actuators are installed on the leeward surface near the apex of a cone which has a semi-apex angle of 10°. The effectiveness of the plasma actuation under different free-stream velocities and angles of attack is analyzed. The pressure distributions over the conical forebody are measured by both steady and dynamic pressure transducers. The transient dynamic pressure distribution tends to gradually become steady as the free-stream velocity increases, that is, the pulsed actuation approximates a continuous one. Furthermore, the flow control effectiveness becomes less noticeable as the free-stream velocity or the angle of attack increases under certain controlling electrical parameters.

Numerical investigation of aerodynamic flow actuation produced by surface plasma actuator on 2D oscillating airfoil

Numerical simulation of unsteady flow control over an oscillating NACA0012 airfoil is investigated. Flow actuation of a turbulent flow over the airfoil is provided by low current DC surface glow discharge plasma actuator which is analytically modeled as an ion pressure force produced in the cathode sheath region. The modeled plasma actuator has an induced pressure force of about 2 k Pa under a typical experiment condition and is placed on the airfoil surface at 0% chord length and/or at 10% chord length. The plasma actuator at deep-stall angles(from 5° to 25°) is able to slightly delay a dynamic stall and to weaken a pressure fluctuation in down-stroke motion. As a result, the wake region is reduced. The actuation effect varies with different plasma pulse frequencies, actuator locations and reduced frequencies. A lift coefficient can increase up to 70% by a selective operation of the plasma actuator with various plasma frequencies and locations as the angle of attack changes. Active flow control which is a key advantageous feature of the plasma actuator reveals that a dynamic stall phenomenon can be controlled by the surface plasma actuator with less power consumption if a careful control scheme of the plasma actuator is employed with the optimized plasma pulse frequency and actuator location corresponding to a dynamic change in reduced frequency.

Study of flow induced by sine wave and saw tooth plasma actuators

The effect of plasma actuator that uses saw-tooth or sine-wave shape electrodes on boundary layer flows is experimentally investigated.The measurement results are compared with a corresponding standard configuration (conventional design using two rectangular strip electrodes)-the actuator that produces a nearly two-dimensional horizontal wall jet upon actuation.PIV measurements are used to characterize the actuators in a quiescent chamber.Operating in a steady manner,the new actuators result in the formation of streamwise and spanwise vortices.That is to say,the new actuators render the plasma actuators inducing three-dimensional variations in the shear layer,offering significant flexibility in flow control.The affected flowfield with the new actuators is significantly larger than that with the conventional linear actuators.While the conventional linear actuators affect primarily the boundary layer flow on a scale of about 1 cm above the wall,the new actuators affect the near wall region at a significantly larger scale.This new design broadens the applicability and enhances the flow control effects and it is potentially a more efficient flow control device.

Dielectric barrier plasma dynamics for active aerodynamic flow control

The paper investigates the dynamics of a new multiple bipolar multiple Dielectric Barrier Discharges(DBD)actuator using in large-scale flow control.Particle image velocimetry experiments are performed to characteristic the effectiveness of the multiple bipolar DBD plasma actuator.The results show that the mutual interaction between the electrodes,one major disadvantage of traditional DBD characterized by reverse discharge can be entirely avoided,and a constantly accelerating electric wind velocity can be obtained by using the new multiple bipolar DBD plasma actuator.

Review of actuators for high speed active flow control

Actuators are one of the key points for the development of active flow control technology.Efficient methods of high speed flow control can provide enhanced propulsive efficiency and at the same time enable safe and maneuverable high speed flight.The development of high speed flight technology promotes the emergence of novel and robust actuators.This review introduces the state of the art in the development of actuators that can be used in high speed active flow control.The classification and different operation criteria of the actuators are discussed.The specifications,mechanisms and applications of various popular actuator types including fluidic,mechanical,and plasma actuators are described.Based on the realistic need of high speed flow control and the existing results of actuators,a new actuator design method is proposed.At last,the merits and drawbacks of the actuators are summarized and some suggestions on the development of active flow control technology are put forward.

Aerodynamic actuation characteristics of radio-frequency discharge plasma and control of supersonic flow

In this paper, aerodynamic actuation characteristics of radio-frequency(RF) discharge plasma are studied and a method is proposed for shock wave control based on RF discharge. Under the static condition, a RF diffuse glow discharge can be observed; under the supersonic inflow, the plasma is blown downstream but remains continuous and stable.Time-resolved schlieren is used for flow field visualization. It is found that RF discharge not only leads to continuous energy deposition on the electrode surface but also induces a compression wave. Under the supersonic inflow condition, a weak oblique shock wave is induced by discharge. Experimental results of the shock wave control indicate that the applied actuation can disperse the bottom structure of the ramp-induced oblique shock wave, which is also observed in the extracted shock wave structure after image processing. More importantly, this control effect can be maintained steadily due to the continuous high-frequency(MHz) discharge. Finally, correlations for schlieren images and numerical simulations are employed to further explore the flow control mechanism. It is observed that the vortex in the boundary layer increases after the application of actuation, meaning that the boundary layer in the downstream of the actuation position is thickened. This is equivalent to covering a layer of low-density smooth wall around the compression corner and on the ramp surface, thereby weakening the compressibility at the compression corner. Our results demonstrate the ability of RF plasma aerodynamic actuation to control the supersonic airflow.

Experimental Investigation of the Effects of Various Plasma Actuator Configurations on Lift and Drag Coefficients of a Circular Cylinder Including the Effects of Electrodes

In this paper, the effects of the existence of plasma actuator electrodes and also various configurations of the actuator for controlling the flow field around a circular cylinder are experimentally investigated. The cylinder is made of PVC （Polyvinyl Chloride） and considered as a dielectric barrier. Two electrodes are fiush-mounted on the surface of the cylinder and are connected to a DC high voltage power supply lbr generation of electrical discharge. Pressure distribution results show that the existence of the electrodes and also the plasma are able to change the pressure distribution around the cylinder and consequently the lili and drag coefficients. It is found that the effect of the existence of the electrodes is comparable with the effect of plasma actuator in con- trolling the flow field around the cylinder and this effect is not reported by other researchers. Eventually it is concluded that the existence of the electrodes or any extra obiects on the cylinder and also the existence of the plasma are capable of changing the flow field structure around the cylinder so that the behavior of the lift and drag coefficients of the cylinder will be changed significantly.