Investigation of Endwall Flow Behavior with Plasma Flow Control on a Highly Loaded Compressor Cascade

To discover the flow behavior in the endwall region and mechanism of plasma flow control on a highly loaded compressor cascade, distributions of static pressure coefficient, total pressure loss coefficient and streamline pat- tern were investigated. Results show that cross flow from the pressure surface to neighboring suction surface ex- ists under pitch-wise pressure gradient. The deflected endwall boundary layer flow interacts with the incoming flow, and then both of them leave off the endwall in tile form of a span-wise vortex. Effect of angle of attack on static pressure is greater than that of free stream velocity. The distinct variations of total pressure loss with end- wall actuations are mainly located within the outer verge of a triangular area with high total pressure loss. Effect of pitch-vAse actuation on separated flows is much better than that of stream-wise actuation, and both enhance with the increase of angle of attack and actuation strength. An efficient method for plasma flow control in the endwall region is the increase of actuation strength, such as adjusting discharge voltage or changing plasma power supply.

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.

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.

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.

Investigation of dielectric barrier discharge plasma flow control

Effects of plasma flow control are researched on the basis of plasma exciting flow experiments and numerical simulations. Turbulent model is more effective than laminar model in plasma numerical simulation as results showed. Both plasma exciting effects of acceleration and flow separation suppression are investigated through experiments carried on the flat plate and the compressor cascades. The results demonstrate that boundary layer characteristic is modified by plasma exciting. Distributions of total pressure and velocity in the wake are improved notably for 20 m/s coming velocity and the effect of plasma can still be observed while velocity is increased to 50 m/s. For low velocity flow, plasma exciting is effective in flow separation suppression.

Experimental Investigation of Flow Separation Control Using Dielectric Barrier Discharge Plasma Actuators

Influence of plasma actuators as a flow separation control device was investigated experimentally. Hump model was used to demonstrate the effect of plasma actuators on external flow separation, while for internal flow separation a set of compressor cascade was adopted. In order to investigate the modification of the flow structure by the plasma actuator, the flow field was examined non-intrusively by particle image velocimetry measurements in the hump model experiment and by a hot film probe in the compressor cascade experiment. The results showed that the plasma actuator could be effective in controlling the flow separation both over the hump and in the compressor cascade when the incoming velocity was low. As the incoming velocity increased, the plasma actuator was less effective. It is urgent to enhance the intensity of the plasma actuator for its better application. Methods to increase the intensity of plasma actuator were also studied.

Numerical Investigation of Plasma Active Flow Control

Based on the theory of EHD （electronhydrodynamic）, a simplified volume force model is applied to simulation to analyze the traits of plasma flow control in flow field, in which the cold plasma is generated by a DBD （dielectric-barrier-discharge） actuator. With the para- electric action of volume force in electric field, acceleration characteristics of the plasma flow are investigated for different excitation intensities of RF （radio frequency） power for the actuator. Furthermore, the plasma acceleration leads to an asymmetric distribution of flow field, and hence induces the deflection of jet plume, then results in a significant deflection angle of 6.26° thrustvectoring effect. It appears that the plasma flow control technology is a new tentative method for the thrust-vectoring control of a space vehicle.

EXPERIMENTAL INVESTIGATION ON INDUCED FLOW VELOCITY OF PLASMA AERODYNAMIC ACTUATION

Plasma flow control is an active flow control technology that based on the plasma aerodynamic actuation. It can be used to enhance the aerodynamic characteristics of aircraft and propulsion systems. To study the phenomena occurring in plasma aerodynamic actuation and the mechanism of plasma flow control, the induced flow velocity of the plasma aerodynamic actuator is experimentally investigated under a variety of parameter conditions. The results indicate that plasma aerodynamic actuation accelerates the near surface air at velocities of a few meters per second, and there is an angle about 5° between the mainstream and the actuator wall and a spiral vortex is formed when the induced flow is moving along the wall. Besides, with the fixed frequency, the induced flow velocity increases linearly with the applied voltage, but it is insensitive to the frequency when the applied voltage is fixed. And the configuration is an effective factor for the performance of the plasma aerodynamic actuator.

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.

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.

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.

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.

Forebody asymmetric vortex control with extended dielectric barrier discharge plasma actuators

Plasma control of forebody asymmetric vortices is mostly achieved by means of dielectric barrier discharge(DBD)plasma actuators. However, DBD actuators suffer from some disadvantages such as a weak induced body force, a singledirection induced jet, and an unclear control mechanism. We carry out wind tunnel experiments involving the forebody vortex control of a slender body at high angles of attack using an innovative extended DBD actuator, which has a stronger capacity to induce an electric wind than a DBD actuator. Through synchronous measurements of the pressure distribution and particle image velocimetry(PIV), the spatiotemporal evolution of the dynamic interactions between plasma-actuationinduced vortices and forebody asymmetric vortices is analyzed. The influence of plasma discharge on the boundary layer separation around a slender body and the spatial topological structures of asymmetric vortices are further surveyed, as the optimized actuation parameters. Extended DBD actuators are found to be more capable of controlling asymmetric vortices than DBD actuators, and a linear proportionality of the sectional lateral force versus the duty ratio is achieved.There exists an optimal normalized reduced frequency( f+= 2π fpd/U∞= 2.39) for asymmetric vortex control under the present experimental conditions. The research results can provide technical guidance for the control and reuse of forebody asymmetric vortices.

Integrated design and performance optimization of three-electrode sliding discharge plasma power supply

The three-electrode sliding dielectric barrier discharge(TES-DBD) plasma actuator significantly enhances the ionization rate and momentum exchange between charged particles and neutral particles by incorporating a parallel DC electrode into the standard DBD design. This design improves the body force and induced jet velocity while allowing flexible control of the induced jet angle, overcoming the limitations of discharge extension and uncontrollable direction in traditional DBD plasma actuators. An integrated plasma power supply has been designed specifically for TES-DBD plasma actuators, streamlining the power supply management. The methodology involves designing the circuit topology for the TES-DBD power supply, followed by simulating and validating its operating principles using Multisim software. The operational performance of the power supply is evaluated through a comprehensive analysis of its electrical,thermal, and aerodynamic properties specific to TES-DBD plasma actuation.

Spatiotemporal evolution laws of sector-shaped dielectric-barrier-discharge plasma actuator

Dielectric barrier discharge(DBD)plasma actuators are widely used in active flow control due to their simple design and rapid responsiveness.However,they need more effectiveness and discharge extension.To overcome these limitations,a sector-shaped dielectric barrier discharge(SS-DBD)plasma actuator with an adjustable jet angle was developed to enhance flow control effectiveness.The flow field dynamics induced by the SS-DBD plasma actuator were quantitatively analyzed using particle image velocimetry(PIV).Experimental investigations showed that precise adjustments to the actuation voltage can modulate the maximum velocity of the induced jet.Furthermore,a quasi-linear relationship between the sector-shaped angles of the SS-DBD and the deflected jet angles was established,indicating that changes in the sector-shaped angles directly influence the direction of the deflected jet.This correlation enables precise control over jet angles,significantly enhancing flow control by adjusting the SS-DBD-PA's sector-shaped angle.

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-to- drag 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.

Flow Control over a Conical Forebody by Duty-Cycle Actuations

Duty-cycle modulation alternately blowing from two opposite-facing plasma actu- ators on the leeward surface near the apex of a cone with a 10° semi-apex angle is adopted to control mean lateral force and moment, and the flow control mechanisms are presented. Pressure distributions over the forebody of the cone are measured by steady pressure tappings. The experiments are performed in a 3.0×1.6 m open-circuit wind tunnel at a wind speed of 20 m/s, a 45° angle of attack and a Reynolds number of 2×10^5, based on the diameter of the base of the cone. Almost linearly proportional control of the lateral forces and moments over a slender conical forebody at a high angle of attack has been demonstrated by employing a pair of single dielectric barrier discharge plasma actuators near the apex of the cone, combined with a duty-cycle tech- nique. The pressure distribution measurements indicate that the hi-stable vortex pattern appears to be shifted in the opposite direction when the port or starboard actuator is activated, while the other is kept off during the test. It is shown that the reduced pulse-repetition frequency based on the local diameter at the plasma actuator equal to one yields the highest effectiveness among the cases considered.

Numerical Investigation of Electrohydrodynamic (EHD) Flow Control in an S-Shaped Duct

An electrohydrodynamic （EHD） method, which is based on glow discharge plasma, is presented for flow control in an S-shaped duct. The research subject is an expanding channel with a constant width and a rectangular cross section. An equivalent divergence angle and basic function are introduced to build the three-dimensional model. Subsequently, the plasma physical models are simplified as the effects of electrical body force and work （done by the force） on the fluid near the wall. With the aid of FLUENT software, the source terms of momentum and energy are added to the Navier-Stokes equation. Finally, the original performance of three models （A, B and C） is studied, in which model A demonstrates better performance. Then EHD control based on model A is discussed. The results show that the EHD method is an effective way of reducing flow loss and improving uniformity at the duct exit. The innovation in this study is the assessment of the EHD control effect on the flow in an S-shaped duct. Both the parametric modeling of the S-shaped duct and the simplified models of plasma provide valuable information for future research on aircraft inlet ducts.

Shockwave–boundary layer interaction control by plasma aerodynamic actuation:An experimental investigation

The potential of controlling shockwave-boundary layer interactions （SWBLIs） in air by plasma aerodynamic actua- tion is demonstrated. Experiments are conducted in a Mach 3 in-draft air tunnel. The separation-inducing shock is generated with a diamond-shaped shockwave generator located on the wall opposite to the surface electrodes, and the flow properties are studied with schlieren imaging and static wall pressure probes. The measurements show that the separation phenomenon is weakened with the plasma aerodynamic actuation, which is observed to have significant control authority over the inter- action. The main effect is the displacement of the reflected shock. Perturbations of incident and reflected oblique shocks interacting with the separation bubble in a rectangular cross section supersonic test section are produced by the plasma actuation. This interaction results in a reduction of the separation bubble size, as detected by phase-lock schlieren images. The measured static wall pressure also shows that the separation-inducing shock is restrained. Our results suggest that the boundary layer separation control through heating is the primary control mechanism.

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(■) 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.