Plasma Actuator Research Articles

Film Cooling Effectiveness Enhancement on Wall Surface with Crater Hole and Sdbd Plasma Actuation

Film Cooling Effectiveness Enhancement on Wall Surface with Crater Hole and Sdbd Plasma Actuation

Improved performance of polyimide Cirlex‐based dielectric barrier discharge plasma actuators for flow control

AbstractDielectric barrier discharge (DBD) plasma actuators are simple electrohydrodynamic devices, which are able to provide effective aerodynamic control. One of the main components of these devices is the thin dielectric layer, which allows to separate and prevent the arc between the high‐voltage electrodes. Different materials can be used as dielectric layer to reduce the power consumption or boost the flow controlling effect of the actuators. In this context, this report presents a comparative study of two commercial polyimides, Kapton and Cirlex, used as dielectric layer of surface DBD plasma actuators. The electrical, dielectric, mechanical, electromechanical, and thermal properties were obtained to evaluate overall performance. It was verified that Cirlex (8.3 W) consumes less power than Kapton (21.3 W) to generate higher induced flow velocity of ≈3.4 m/s for an input voltage of 11 kVpp and 24 kHz. During one AC cycle at 11 kVpp the charge transferred for Cirlex (70 nC) is lower than for Kapton (100 nC), as well as the dielectric breakdown voltage to ignite the plasma discharge, 1.5 and 2.2 kVpp, respectively. The Cirlex DBD presents a higher voltage operation limit (at least 14 kVpp) and a more regular plasma discharge, which results in a more homogenous thermal profile and temperature distribution during its operation. The Cirlex actuator delivered higher mechanical power (6.2 mW) and achieved higher electromechanical efficiency (0.004%). The polyimide Cirlex proved to be a suitable alternative for Kapton to fabricate DBD plasma actuators for flow control with improved performance.

Dynamic Burst Actuation to Enhance the Flow Control Authority of Plasma Actuators

A computational study was conducted on flows over an NACA0015 airfoil with dielectric barrier discharge (DBD) plasma. The separated flows were controlled by a DBD plasma actuator installed at the 5% chord position from the leading edge, where operated AC voltage was modulated with the duty cycle not given a priori but dynamically changed based on the flow fluctuations over the airfoil surface. A single-point pressure sensor was installed at the 40% chord position of the airfoil surface and the DBD plasma actuator was activated and deactivated based on the strength of the measured pressure fluctuations. The Reynolds number was set to 63,000 and flows at angles of attack of 12 and 16 degrees were considered. The three-dimensional compressible Navier–Stokes equations including the DBD plasma actuator body force were solved using an implicit large-eddy simulation. Good flow control was observed, and the burst frequency proven to be effective in previous fixed burst frequency studies is automatically realized by this approach. The burst frequency is related to the characteristic pressure fluctuation; our approach was improved based on the findings. This improved approach realizes the effective burst frequency with a lower control cost and is robust to changing the angle of attack.

Highly responsive multi-flow pattern generation by multi-electrode plasma actuator using a single power supply

A dielectric-barrier-discharge plasma actuator (DBD-PA) is an active flow-control device that uses ionic wind generated by electrohydrodynamic forces. A DBD-PA controls fluid motion and offers quick response without the need for moving parts. Previous studies have proposed methods for generating various flow patterns with a DBD-PA for fluid control. This paper presents a method for generating multiple flow patterns using a multi-electrode DBD-PA that is driven by a single-channel high-voltage power supply with a relay circuit. In contrast, conventional methods of realizing multiple flow patterns involve the use of a multi-channel power supply. Hence, they have the disadvantage of requiring a complicated power supply system. The proposed method succeeded in realizing several induced-flow modes involving the generation of a directionally controllable wall jet, various sizes of vortices, and an upward jet by altering the switching frequency and switching ratio. In addition, our experimental results indicate that the proposed method can control the flow pattern with a significantly short response time. The direction of the wall jet can be switched within tens to hundreds of milliseconds. Therefore, the proposed method combines simplicity and versatility and is expected to facilitate the realization of multifunctional active flow control in various flow fields, such as flow turbulent boundary layer control, thermal diffusion control, gas mixing, and flame-stability enhancement.

Numerical simulation of the flow around a square cylinder under plasma actuator control

Navier–Stokes computations are performed, and detailed results are documented on the vortex shedding, lift and drag fluctuations, and their spectra for flow past a square cylinder with the Reynolds number ranging from 1 to 300. A body force model for the dielectric barrier discharge (DBD) plasma actuator is used in the Navier–Stokes computations to study the effectiveness of flow control by a pair of the DBD actuators. Three installation configurations of the actuators are investigated. The effects of the actuator location, actuator input power, and the flow Reynolds number are studied. In the first case, two actuators have been installed on the top and bottom of the cylinder. In the second case, two actuators are installed on the front surface. In the last case, two actuators are installed on the rear surface. It is discovered that the best flow control effect is achieved in the last case. Both the unsteady vortex shedding and the average drag can be significantly reduced by the plasma actuators. Under best conditions, the vortex shedding in the wake can be completely suppressed.

Drag reduction of circular cylinder using linear and sawtooth plasma actuators

The flow around a single circular cylinder modified by the Dielectric Barrier Discharge (DBD) plasma actuator is investigated experimentally at a Reynolds number Re = 5.25 × 103. The main purpose of the present study is to establish a comprehensive understanding of the effects of linear and sawtooth DBD plasma actuators (under steady and unsteady actuation modes, with different applied voltage Va, normalized modulation frequency F+, and duty cycle DC) on the time-averaged drag coefficient CD and flow characteristics of the cylinder. Extensive measurements are performed in the near wake of the cylinder using a load cell, hotwire anemometer, flow visualization, and particle image velocimetry techniques. The maximum drag reductions are 58% and 22.8% under the steady and unsteady actuation modes of the linear actuators, respectively, when a voltage of Va = 11 kV is applied. On the other hand, the maximum drag reductions achieved by the steady and unsteady actuation modes of the sawtooth actuators are 51.8% and 53.0%, respectively. The corresponding power efficiencies are 1.6%, 0.9%, 1.4%, and 2.1%, respectively. A detailed examination of the near wake dynamics unveils that the mechanisms behind the substantial drag reductions are quite different for the two different actuators, which account for the difference in drag reduction and efficiency.

Manipulation of ramp-induced shock using an array of surface arc plasma actuators

Ramp-induced shock under the disturbance of a surface arc plasma actuator array was experimentally investigated using high-speed Schlieren imaging in a Ma = 2 flow. Shock is generated by a compression ramp at a 26° angle, which is installed on a flat plate. Two incoming boundary layer flows, namely turbulent and laminar, are selected to interact with the ramp-induced shock. Four actuators in an array are placed upstream of the ramp corner in a spanwise direction to generate the perturbations. The results indicate that a 10 mm arc length discharge is the ideal electrode gap at such low pressure due to the generated perturbations with larger affected area and longer duration time. With increasing energy deposition, the thermal gas bulb increases, and the weakening effect on the ramp shock is enhanced. Experiments under high Reynolds number show that the thermal gas bulbs are observed to interact with the turbulent boundary first, which implies a highly vortical activity occurring in the boundary layer acting as the boundary layer thickens mechanism to control the shock.

Evaluation of Cylindrical Asymmetric Surface Dielectric Barrier Discharge Actuators for Surface Decontamination and Mixing

Surface dielectric barrier discharge (SDBD) was used to evaluate cylindrical plasma actuators for inactivation of Salmonella enterica. A cylindrical SDBD configuration was evaluated to determine if the inherent induced body force could be leveraged to impel plasma species, such as reactive oxygen and nitrogen species (RONS), as an apparatus to sterilize surfaces. The cylindrical structure is evaluated in this study to observe whether an increase in mixing is possible to efficiently distribute the plasma species, thereby improving bacterial inactivation efficiency. The increase in induced airflow of SDBD actuators with increased numbers of electrodes correlates with increased bacterial inactivation. These results suggest that improving the particle velocity, airflow mixing tendencies, and plasma volume for the same power inputs (same net power to the actuators) results in increased surface decontamination efficiency.

Experimental investigation of supersonic boundary-layer tripping with a spanwise pulsed spark discharge array

In this paper, a pulsed spark discharge plasma actuator array is deployed to control laminar–turbulent transition in a Mach 3.0 flat-plate boundary layer, and the subtle flow structures are visualized by nanoparticle planar laser scattering (NPLS) technique. Results show that the onset location of turbulence can be brought upstream by plasma actuation, corresponding to forced boundary-layer transition. Hairpin vortex packets evolved from the thermal bulbs play a vital role in the breakdown of laminar flow. With the help of a machine learning tool, all the relevant structures induced by plasma actuation are extracted from NPLS images, and a conceptual model of the hairpin vortex generation is proposed, including three stages: production and lift-up of the high-vorticity region, formation of the $\varLambda$ vortex and evolution of the hairpin vortex.

Ice shape modulation with nanosecond pulsed surface dielectric barrier discharge plasma actuator towards flight safety

Ice accretion on aircraft wings seriously damage the aerodynamic performance and flight safety of an aircraft. To deal with this issue, a leading-edge ice shape modulation method using nanosecond pulsed surface dielectric barrier discharge (nSDBD) is proposed, featuring the merit of less energy consumption when compared to full-wing de-icing. A set of wind tunnel experiments are conducted for verification purposes. Results show that the dangerous continuous ice can be modulated into periodically segmented ice pieces by nSDBD, forming a wavy leading edge, and the energy consumption of ice shape modulation is less than 50% of that of complete deicing. In the case of NACA0012 airfoil, ice shape modulation can improve the lift noticeably at each angle of attack (0° to 22°), delay the stall angle by 2°, and reduce the drag coefficient by more than 50% compared to full ice condition. The duration of ice shape modulation with plasma actuators lasts for about 4 min to 6 min. For flow separation control, the coherent streamwise vortices generated by the wavy leading edge are able to enhance the mixing between the boundary layer and the freestream, resulting in an increase of the ability to resist the adverse pressure gradient above the airfoil. Since both ice shape modulation and flow separation control benefit the aerodynamic performance of icing airfoils, the flight safety is improved.

Plasma-Based Dynamic Stall Control and Modeling on an Aspect-Ratio-One Wing

Quasi-static and dynamic stall control experiments, using dielectric barrier discharge plasma actuators, were performed on a square-tipped aspect-ratio-one wing, with a NACA 0015 profile, under harmonic pitching, at a Reynolds number of . Relatively low and relatively high pulse-modulated reduced excitation frequencies were introduced at the leading edge; the former produced the largest poststall lift improvements, whereas the latter produced the highest maximum lift. A reduced frequency, based on laminar separation bubble shedding, was enlisted to explain the differences between the two results. Under conditions of dynamic pitching, evidence of a dynamic stall vortex was absent, due to its interaction with the strong tip vortices, consistent with prior experimental and numerical investigations. As a general rule, performance benefits produced by excitation under quasi-static conditions were reproduced under harmonic pitching. Low-order dynamic stall and dynamic stall control models, based on a modified version of the Goman–Khrabrov delta-wing concept, were evaluated. Model constants were obtained from quasi-static data sets, and a single baseline dynamic case was employed to determine the time constants. The model produced excellent results for both baseline and controlled cases, which was attributed to similar lift and stall mechanisms exhibited by delta and rectangular low-aspect-ratio planforms.

A high-performing sawtooth plasma actuator with multi-electrodes

The present study for the first time develops a high performing sawtooth plasma actuator (PA) that may produce large flow velocity u and streamwise vorticity ωx′ by means of increasing the number of electrodes. This improved performance is crucial for improving the post-stall airfoil aerodynamics. It is found that the high performing sawtooth PA with three encapsulated electrodes powered by +Vdc (hereafter called the optimum sawtooth PA) produces the maximum ωx′ and u of 650 s−1 and 6.83 m/s, respectively. The plasma-induced flow is linked to the acceleration of the negatively charged species in the streamwise direction caused by the +Vdc-powered encapsulated electrodes and is 26.5% larger than that produced by a standard sawtooth PA (with two sawtooth electrodes) under the same power consumption. At a chord Reynolds number Re=1.0×105, the optimum sawtooth PA under steady mode actuation postpones the stall angle-of-attack α of a NACA 4412 airfoil by 4° and increases the maximum lift coefficient CL by 8.1%; the former is appreciably larger than that (0°) achieved by the standard sawtooth PA. Furthermore, under the optimum burst mode actuation (non-dimensional burst frequency F+=1.4 and duty cycle DC=7%), the stall α and the maximum CL increase by 5° and 19.6%, respectively, along with a 93% power saving. The physical mechanisms behind the impressive performance are discussed.

Characteristics of a dielectric barrier discharge plasma actuator driven by pulsed-DC high voltage

Dielectric barrier discharge using pulsed-DC high voltage (pulsed-DC DBD) have been proven to be capable of effectively reducing skin friction drag in turbulent boundary layers with limited power consumption, thus producing significant net power savings. In this work, the characteristics of pulsed-DC DBD, including power consumption, induced flow structure, thermal effect, and body force, are investigated sequentially. Both the power consumption and pressure waves produced by pulsed-DC DBD are similar to that of DBD using nanosecond pulses (ns-DBD), whereas the wall-bounded jet structure resembles that of DBD using sinusoidal high voltage (ac-DBD). A curved wall jet is induced at a small pulse width, which turns into a straight one due to the combined effect of momentum and thermal addition when the pulse width increases. With increasing pulse width, the induced body force goes up while the thermal effect weakens. Although pulse frequency has no impact on the wall-bounded jet topology, the body force increases with pulse frequency because of the enhanced energy entrainment. With these results, four parameters that affect the performance of pulsed-DC DBD are extracted, including the pulse leading edge, pulse width, frequency, and amplitude, which lays the foundation for the optimization of pulsed-DC DBD.

Fundamental investigation using active plasma control to reduce blade–vortex interaction noise

Blade vortex interaction noise is a problematic and dominant component of rotor noise. Plasma actuators strategically placed at the tip of the rotor blades can reduce the strength of the tip vortices. This reduction has the potential to significantly reduce blade vortex interaction noise. A combined experimental, numerical, and theoretical program shows supporting evidence that low power plasma actuators can effectively lower coherence of the blade tip vortex and reduce blade vortex interaction noise over-pressure by up to 80%. For a nominal small five-bladed unmanned aerial vehicle, we predict an approximate 8.88 maximum ΔdB reduction for a 150 m/s tip speed. Experimental, computational, and acoustic modeling support these predictions. This study represents a fundamental investigation in the fixed-frame, which provides evidence for higher level research and testing in a rotating framework.

Stochastic forcing of the 2D boundary layer by DBD plasma actuator

The paper describes the results of the parametric study of the broadband velocity pulsations, induced by DBD plasma actuator in 2D subsonic boundary layer. The presented data include the analysis of the disturbance growth at various pressure gradients. It is assumed that the broadband pulsations are composed of the elementary disturbances, induced by an individual microdischarges, wandering along the electrode edge. These disturbances have a streak-like structure in a near field, and evolve into a fan of packets of Tollmien-Schliechting waves as one moves downstream. The streamwise length, needed for transition to modal behavior, depends on the stability properties of the boundary layer.

Experimental study on the plasma actuators for the tip leakage flow control in a turbine cascade

In this paper, the effects of dielectric barrier discharge (DBD) plasma actuators (PAs) on the leakage flow structures and loss in a turbine cascade have been experimental studied. Two group cases have been conducted to evaluate the performance of the DBD plasma actuators and its effect varied with the attack angle (α). By measuring the static pressure on the casing and the flow field at the exit section, the effects of the DBD PAs have been illustrated. Results show that the DBD plasma actuators on the tip of turbine cascade could make effect on the tip leakage flow by weaken the strength of the TLV near the casing. Rising the actuation strength, this effect would be enhanced. Besides, this effect on the flow structure mainly focuses on the TLV near the casing, changes in the blade passage could be ignored with the action of the DBD PAs. In the study on the attack angle, the largest loss reduction of 7.8% is noticed with the inflow Re=0.64×105 and α=5°.

Flow separation control in S-shaped ∼inlet with a nanosecond pulsed surface dielectric barrier discharge plasma actuator

A nanosecond pulsed surface dielectric barrier discharge (nSDBD) plasma actuator is proposed to eliminate the complex 3D flow separation in an S-shaped ∼engine inlet. A set of wind tunnel experiments based on pressure measurements are conducted to verify the flow control effectiveness and obtain the influence laws of actuation voltage, pulse frequency, actuator layout and coverage area. The results show that nSDBD can effectively eliminate flow separation, leading to a noticeable improvement in the total pressure distribution at the outlet, manifested as a reduction in the low-pressure zone and an extension of the high-pressure zone. The spanwise layout nSDBD delivers a better flow control effect compared to the streamwise layout. For the same geometrical layout, the flow control effect improves with increasing voltage, and the optimal actuation frequency corresponds to a Strouhal number of approximately F + = 0.5. In particular, with a spanwise array of nSDBD plasma actuators operating at V p-p = 10 kV and F + = 0.5, the flow separation region is completely suppressed. The mechanism of flow separation with nSDBD can be ascribed to the mixing enhancement between the boundary layer and the main flow, which improves the boundary layer’s ability to resist the adverse pressure gradient.

Flow Control for Unmanned Air Vehicles

The pervasiveness of unmanned air vehicles (UAVs), from insect to airplane scales, combined with active flow control maturity, has set the scene for vehicles that differ markedly from present-day configurations. Nano and micro air vehicles, with characteristic Reynolds numbers typically less than 105, rely on periodically generated leading-edge vortices for lift generation, propulsion, and maneuvering. This is most commonly achieved by mechanical flapping or pulsed plasma actuation. On larger UAVs, with Reynolds numbers greater than 105, externally driven and autonomous fluidic systems continue to dominate. These include traditional circulation control techniques, autonomous synthetic jets, and discrete sweeping jets. Plasma actuators have also shown increased technological maturity. Energy efficiency is a major challenge, whether it be batteries and power electronics on nano and micro air vehicles or acceptably low compressor bleed on larger UAVs. Further challenges involve the development of aerodynamic models based on experiments or numerical simulations, as well as flight dynamics models.

Bypass transition in a boundary layer flow induced by plasma actuators

Bypass transition in flow over a flat plate triggered by a pair of dielectric-barrier-discharge plasma actuators mounted on the plate surface and aligned in the streamwise direction is investigated. A four-species plasma–fluid model is used to model the electrohydrodynamic force generated by the plasma actuation. A pair of counter-rotating streamwise vortices is created downstream of the actuators, leading to the formation of a high-speed streak in the centre and two low-speed streaks on each side. As the length of actuators increases, more momentum is added to the boundary layer and eventually a turbulent wedge is generated at an almost fixed location. With large spanwise distance between the actuators (wide layout), direct numerical simulations indicate that the low-speed streaks on both sides lose secondary stability via an inclined varicose-like mode simultaneously, leaving a symmetric perturbation pattern with respect to the centre of the actuators. Further downstream, the perturbations are tilted by the mean shear of the high- and low-speed streaks and consequently a ‘W’-shaped pattern is observed. When the pair of plasma actuators is placed closer (narrow layout) in the spanwise direction, the mean shear in the centre becomes stronger and secondary instability first occurs on the high-speed streak with an asymmetric pattern. Inclined varicose-like and sinuous-like instabilities coexist in the following breakdown of the negative streaks on the side and the perturbations remain asymmetric with respect to the centre. Here the tilting of disturbances is dominated by the mean shear in the centre and the perturbations display a ‘V’ shape. Linear analysis techniques, including biglobal stability and transient growth, are performed to further examine the fluid physics; the aforementioned phenomena at narrow and wide layouts, such as the secondary instabilities, the ‘V’ and ‘W’ shapes, and the symmetric and asymmetric breakdown, are all observed.

Control of leading-edge vortices over delta wing using flow control methods: A review

The main objective of this research is to study various methods to control flow field over the delta wings. The flow control methods are of two types: active and passive flow control. Active flow control technique involves the addition of energy from an external source to the main flow. The various active flow control techniques comprise of pneumatic devices such as blowing and suction near the leading-edge, plasma actuators, steady/unsteady excitation and control surfaces. The passive flow control technique involves the modification to the delta wing geometry and does not involve any external source of energy. The passive flow control methods comprise of generation of multiple vortex arrangement and alteration of leading-edge shapes. The effect of flow control technique on the parameters such as flow reattachment, location of leading-edge vortices and breakdown are presented in this research.