Dielectric Barrier Discharge Actuator Research Articles

Dielectric barrier discharge actuators: Momentum injection into co-flow and counter-flow freestream

In a quiescent environment, dielectric barrier discharge (DBD) plasma actuators generate a wall jet through the interaction of ionized and neutral molecules in an electric field. In external flow, the coupling between electrohydrodynamic (EHD), turbulence, inertial, and viscous effects in the flow boundary layer is more complex and requires additional investigation. We experimentally study momentum injection by DBD actuators into the free stream flow with Re = 35,000 and 75,000 in co-flow and counter-flow scenarios over a range of VAC = 12 kV–19.5 kV peak-to-peak at a frequency of 2 kHz. In co-flow, the momentum injection leads to boundary layer thinning and fluid entrainment from the freestream into the DBD forcing region, while in the counter-flow configuration, flow separation can occur. A separation bubble is observed at Re = 35,000 for the tested condition. The momentum difference in the counter-flow configuration is six times greater than the EHD jet momentum in a quiescent environment. Both co-flow and counter-flow momentum injections show diminishing effects with higher Re. We show that the resulting flow pattern is not a superposition of the EHD jet and the free stream but is determined by the coupling and competition of inertial, viscous, and Coulombic effects between the EHD-driven forcing and the external flow. The proposed non-dimensional momentum ratio (M*) of EHD jet momentum to momentum in the external flow boundary layer can be used to predict the onset of separation; however, additional experimental and numerical studies are required to generalize this concept to other flow scenarios. The velocity profiles and momentum measurements presented here can be used to validate numerical models and inform the design of DBD actuators for active flow control.

Investigation of coherent structures in low-speed turbulent boundary layers controlled by AC-DBD plasma actuators

The dielectric barrier discharge (DBD) actuator has the advantages of being lightweight, having no moving parts, ease of use, and fast response, and has received widespread attention in flow control applications. Turbulence boundary layer drag reduction is one of many applications of DBD flow control, but the mechanism of DBD actuator turbulence drag reduction needs further investigation. The effect of DBD excitation on the skin-friction drag of a turbulent boundary layer on a flat plate at different flow speeds was investigated experimentally. The change in skin-friction drag was measured using oil film interferometry, and the velocity distribution within the boundary layer was obtained using a particle image velocimetry system. The results showed that under the action of the plasma actuator, the local skin-friction coefficient was measured to decrease by 49%. Through dynamic mode decomposition, plasma actuators can increase the thickness of the low-velocity region in the boundary layer, reduce the intensity of Q2 and Q4 events, and inhibit the development of coherent structures, thereby achieving drag reduction.

A Numerical Investigation of Supersonic Combustion Flow Control by Nanosecond-Pulsed Actuations

The efficiency of supersonic combustion is largely dependent on inlet and injection parameters. Additional energy input is required in some off-design conditions, and nanosecond discharge actuation can be a solution. In the present study, a phenomenological model of a nanosecond-pulsed surface dielectric barrier discharge (NS-SDBD) actuator was developed to analyze the combustion enhancement effect for a supersonic combustor with transverse H2 injection. A seven-reaction H2–air combustion model was adopted for the numerical simulation. Dynamic mode decomposition (DMD) was employed to acquire temperature perturbation in spatial and temporal domains. The results show that the actuator provides additional temperature-increment and species transportation through compression waves. The combustion enhancement effect is mainly attributed to the flow perturbation in the shear layer, which promotes the turbulent diffusion of fuel. Given the same power input, the combustion efficiency at the shockwave reflection point is increased by 17.5%, and the flame height is increased by 15.4% at its maximum.

Analytical input-output modelling of surface dielectric barrier discharge plasma actuator

Surface dielectric barrier discharge (SDBD) actuators are a type of asymmetric dielectric barrier discharge (DBD) actuator that can be used to generate ions and produce thrust for near-space vehicles. In this paper, a physics-based model for SDBD produced thrust is developed that accounts for geometric and environmental variation between SDBDs. The presented SDBD analytical model (SDBD-AM) is based on models for parallel-plate DBDs but accounts for the ‘virtual electrode’ resulting from changing plasma length that is particular to SDBDs. To validate the model, thrust measurements from 12 different configurations from previous studies were used, and the mean absolute percentage error (MAPE) between each configuration and SDBD-AM was determined. The observed effects on the model were attributed to structural effects including electrode width, electrode spacing, dielectric, and environmental effects including pressure, and the apparent uncertainties are different for each effect. As a result, it was obtained that the MAPE between SDBD-AM and the experimental data for different structures is 11%, and for different pressures, it is 12%. The body force field has been simulated using SDBD-AM and a distribution function in COMSOL software, and the body force profile near the exposed electrode has been validated with a previous numerical model. This model can be used for the design and optimization of SDBD actuators and also in the design of control systems such as spacecraft attitude control in order to increase the accuracy and performance of the controller.

Experimental Investigation of the Active Flow Control over a Cranked-Delta Wing

A series of experiments was carried out to investigate the effects of active flow control on the aerodynamic characteristics of a cranked-delta-wing model at a subsonic speed. A dielectric barrier discharge (DBD) plasma actuator was used to improve the aerodynamic performance of the half-span cranked-delta-wing model at various angles of attack. The model had inboard and outboard sweepback angles of 57 and 38 deg, respectively. The surface pressure distribution was obtained at five streamwise stations and at two ray stations. All data were obtained at a constant Reynolds number of 0.27×106 and at various angles of attack: 0  deg≤α≤36  deg. The results showed that the pulsed DBD plasma actuator improved the aerodynamic performance of the cranked-delta-wing model by preventing flow separation at high angles of attack. The deep stall angle of attack was delayed up to 6 deg, and the poststall suction coefficient was increased approximately 30% at an angle of attack of about α=34  deg when the pulsed DBD plasma was applied at its optimum condition (F+≈1 and duty cycle=10%). It was found that the pulsed plasma actuator suppressed the wake flow in the forward portion of the wing at poststall angles of attack, thus delaying the flow separation. However, the effects of the DBD actuator at very high angles of attack on the flow reattachment process at the rear portion of the wing for the present DBD setting were seen to be minimal. The induced flow by the pulsed DBD plasma actuator influenced the vortex merging phenomena and delayed the onset of the outer vortex burst at prestall angles of attack.

Parametric study of DBD plasma actuator for heat transfer enhancement in flow over a flat plate at low Reynolds numbers

The present study intends to find the optimal configurations of Dielectric-Barrier-Discharge (DBD) plasma actuators to augment the thermo-hydraulic performance in air flow over a flat plate at low Reynolds numbers. A range of parametric studies are conducted to determine the impact of the major contributing variables; Reynolds number, voltage frequency, and the applied voltage of the DBD actuator, on the heat transfer. This study reports that in the presence of plasma actuation, the factor of enhancement (Num/Num0) achieves about 3.76. Results show that reducing the Reynolds number and raising the frequency and applied voltage of the DBD actuator improve the factor of enhancement. Furthermore, the plasma system thermal efficiency (PSTE) to achieve the optimized electric power consumption and heat transfer augmentation is introduced as the rate of increase of enhancement factor to the rate of increase of consumed electric power. The frequency and applied voltage for the DBD actuator are used as the design variables to find the optimum configurations. Optimum electric power consumption and configurations of DBD plasma actuator based on Reynolds number are determined. Results also show that Vapp = 10.5 kV and f = 5 kHz conditions for DBD plasma actuator is much beneficial than the other configurations in the presence of low Reynolds number external flow. This study's findings will benefit designers in developing high-performance heat transfer.

Spectral Analysis of the Effects of Variation in Electrodes' Area for Dielectric Barrier Discharge Actuator

     In this work, one configuration was used to study the electrical discharge resulting from the dielectric barrier. This configuration consists of a sheet of epoxy/Al composite with dimensions of 75 mm in length, 25 mm in width, and 3 mm in thickness. This panel is located at the center of the electrodes, so that the distance between each of the electrodes and the plate is 2 mm and plasma is generated at these distances. The relationship between voltage and current with changing the frequency of the equipment as well as changing the area of ​​exposure to the upper electrode or changing its length has been studied. The length of the top electrode varies at 0, 10, 20, 30, and 40 mm from the center of the electrodes producing exposure areas of 1875, 1625, 1375, 1125, 875, and 625 mm2, respectively. Two frequencies of 8 and 9 kHz were applied in this work. The results showed that the discharge current increases linearly with the applied input voltage and with the decrease of the exposure of the upper electrode. Then, the current increases with the stability of the voltage in varying proportions depending on the exposure area and frequency. The plasma generated from this modulation was diagnosed with the exposure area and the fitted frequency. Electron temperature and electron density are calculated using the optical emission spectroscopy technique by Boltzmann and Lorenz, respectively. It can be seen that the temperature, electron density, and plasma frequency increase with the decrease of the exposure area, while the Debye length shows the opposite behavior and this is clear in this formation and high effectiveness at Diagnosis and Reason This formation will be adopted in the surface treatment of the aluminum epoxy compound.

Numerical Analysis of Airfoil Flow Control Using a Nanosecond Pulsed Plasma Actuator

The control mechanism of a nanosecond dielectric barrier discharge (NS-DBD) actuator for suppressing laminar separation on airfoils was investigated using two-dimensional scale-adaptive simulations. To model the control effect of the NS-DBD actuator, a surface heating approach based on the analytical solution for transient one-dimensional heat conduction has been used. The focus of the investigation lies in the study of vortex formation and evolution induced by the actuator. A NACA 0015 profile was simulated at 14° with 250,000 chord-based Reynolds number. Regarding energy deposition, a low-energy case and a high-energy case were simulated. Several actuation parameters were varied, including the electrode position and surface temperature. In addition, the influence of constant and temperature-dependent modeling of the kinematic viscosity was investigated. The results for the time-averaged pressure coefficients show excellent agreement with measurement results. High grid resolution in the boundary layer allowed a detailed investigation of the vortex formation process. The main finding is that vortices are generated by baroclinic torque and vortex dilatation and not by a Kelvin–Helmholtz instability. Initially, tiny vortices form at the beginning of the separation region. Subsequently, these vortices are carried downstream and grow in size, thus preventing full separation due to momentum transfer from the external flow.

Surface charge characteristics in surface dielectric barrier discharge actuators with thin cylindrical exposed electrode

The influence of the cylindrical exposed electrode diameter on distribution and attenuation of the surface charge in surface dielectric barrier discharges is experimentally investigated using the Pockels effect of the Bi12SiO20 crystal. For the actuator with the smaller exposed electrode diameter, more positive charges accumulate closer to the exposed electrode after positive half periodic discharge, while the quantity of positive charges deposited on the surface in a discharge period at the same distance away from the exposed electrode is smaller. At the same time, the smaller the exposed electrode diameter is, the shorter decay time the positive charge filament needs. Combined with thrust generation of actuators, it can be indicated that a positive residual surface charge closer to the exposed electrode may play a more crucial role in the discharge and consequent thrust than one far away from the exposed electrode does. Also, the effect on the discharge of the positive residual surface charge may be greater than that of the negative residual surface charge. More explorations of the residual surface charge have been done by selectively enhancing the discharge of the actuator with a 10 μm exposed electrode using the pulse-AC dual power supply, drawing the same conclusions.

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.

Stabilization of a multi-frequency open cavity flow with gradient-enriched machine learning control

We stabilize an open cavity flow experiment to 1 % of its original fluctuation level. For the first time, a multi-modal feedback control is automatically learned for this configuration. The key enabler is automatic in situ optimization of control laws with machine learning augmented by a gradient descent algorithm, named gradient-enriched machine learning control (Cornejo Maceda et al., J. Fluid Mech., vol. 917, 2021, A42, gMLC). The physical interpretation of the feedback mechanism is assisted by a novel cluster-based control law visualization for the flow dynamics and corresponding actuation commands. Starting points of the control experiment are two unforced open cavity benchmark configurations: a narrow-bandwidth regime with a single dominant frequency and a mode-switching regime where two frequencies compete. The flow is forced by a dielectric barrier discharge actuator located at the leading edge and is monitored by a downstream hot-wire sensor over the trailing edge. The feedback law is optimized with respect to the monitored fluctuation level. As reference, the self-oscillations of the mixing layer are mitigated with steady actuation. Then, a feedback controller is optimized with gMLC. As expected, feedback control outperforms steady actuation by achieving a better amplitude reduction with approximately 1 % of the actuation energy required for similarly effective steady forcing. Intriguingly, optimized laws learned for one regime perform well for the other untested regime as well. The proposed control strategy can be expected to be applicable for many other shear flow experiments.

Flow induced by a pair of plasma actuators on a circular cylinder in still air under duty-cycle actuation

A pair of surface mounted dielectric-barrier-discharge (DBD) plasma actuators is placed diametrically on a circular cylinder model. The flow field generated by the actuators in steady and duty-cycle actuation modes is measured by particle image velocimetry. Salient features of the flow and vortices are discovered for the duty-cycle actuation modes with frequency ranging from 5 to 1000 Hz and duty-cycle ratio from 0.01 to 0.99. The results are compared with those for continuous steady actuation. For a given duty-cycle ratio, a discrete vortex is generated by each of the DBD actuator in an actuation cycle for low frequencies. Such vortices are created alternately from each side of the cylinder. They interact and move laterally in response to the on-off signals of the actuators. As the frequency increases, the distance between the vortices generated from successive duty-cycles decreases and the lateral motion of the vortices becomes smaller so that the vortices are packed together as a vortex train along a narrow path on each side of the cylinder. As the frequency is further increased, the vortices in the vortex trains lose their individual characteristics and the vortex trains become steady jets. Regardless of the actuation frequency, the direction of the average total momentum of the air is found to be continuously dependent on the duty-cycle ratio. The magnitude of the average total momentum depends on the frequency. An optimum frequency exists for maximum average momentum, which may exceed that in the continuous steady actuation mode.

Experimental investigation of the natural convection heat transfer characteristics of cylinder walls with a DBD actuator as the heat source

Conventional electric heating methods applied when evaluating the natural convection heat transfer parameters at the outer walls of cylinders produce uneven heat flows and large measurement errors. The present work addresses these issues by developing a new heating method using a dielectric barrier discharge (DBD) actuator as the heat source. An experimental system is constructed, where the thermal power output of the DBD actuator is first measured by calorimetry, and the natural convection heat transfer characteristics of a representative cylinder are analyzed with an explicit accounting of the temperature distribution at the outer wall of the cylinder. The results demonstrate that the DBD actuator can provide more uniform heat flow than conventional electric heaters. The temperature difference between the top and the bottom of the cylinder wall initially increases with increasing thermal power, decreases to a minimum at a thermal power of about 400 W, and subsequently increases with increasing thermal power. In addition, and the feasibility of the DBD actuator as a heat source is demonstrated according to the high degree of conformation between the calculated values and empirically established correlations between Nusselt number, which generally deviate by less than 10%.

Numerical modeling of dielectric barrier discharge actuators based on the properties of low-frequency plasmons

Electrohydrodynamic flow control systems have proven to be among the most promising flow control strategies within previous decades. Several methods for efficient evaluation and description of the effect of such systems are indeed available. Yet, due to these systems’ critical role in various applications, possible improvements are still investigated. A new phenomenological model is presented for the simulation of the plasma actuators based on the electrodynamic properties of low-frequency plasmons. The model simulates the plasmonic region as a dispersive medium. This dissipated energy is added to the flow by introducing a high-pressure region, calculated in terms of local body force vectors, requiring the distribution of the electric field and the polarization field. The model determines the electric field for the computation of the body force vector based on the Poisson equation and implements the simplified Lorentz model for the polarization field. To fully explore the performance of the presented model, an experiment has been conducted providing a comparison between the observed effect of plasma actuators on the fluid flow with the results predicted by the model. The model is then validated based on the results of other distinct experiments and exempted numerical models, based on the exchanging momentum with the ambient neutrally charged fluid, demonstrating that the model has improved adaptability and self-adjusting capability compared to the available models.

Efficiency assessment of a single surface dielectric barrier discharge plasma actuator with an optimized Suzen–Huang model

Spatial and time-resolved characteristics of a single surface dielectric barrier discharge (sDBD) actuator are experimentally and numerically investigated. The paper also focuses on the efficiency of sDBD actuators used as flow-control devices. The motivation is the need for developing a cost-effective way to optimize the balance between control performance and actuator power consumption. The study considers the steady state as often employed in experiments as well as the transient regime. Experimental methods to obtain the active power are revisited, and for the first time, the commonly used simplified phenomenological Suzen–Huang model (SHM) is used for the computation of electrical characteristics. The SHM represents fair qualitative features of the starting vortex. However, it fails when time-resolved velocity profiles are compared. Results show that even with an optimized parametrical analysis of the “tuned” plasma variables, the model is not able to fully reproduce the induced wall-jet neither spatially nor temporally. Furthermore, it underestimates the power consumption by more than 80%. The intrinsic challenge of accurately measuring the alternating current of the DBD and the instantaneous mechanical power, together with the failure of representing time-resolved velocity profiles and the underestimated electric power by the model, highlights that a better phenomenological model including gas dynamics and electric characteristics or using a fully coupled physical plasma model is required.

Approximate Formulations in Mean Models of Dielectric Barrier Discharge Plasma Flow Actuator

A new simplified algorithm is proposed for numerical simulation of dielectric barrier discharge actuators. It is based on a three-species fluid model and includes five ionic reactions. The reaction rate coefficients are calculated from the Boltzmann equation, and the local field approximation is used. To drastically reduce the computing time, the discharge pulses are artificially damped. Two approximate models for photoionization are implemented and compared. This numerical algorithm is an attempt to compromise two approaches previously proposed: full plasma models, requiring prohibitively long computing time, and phenomenological models, which were based on inadequate physics. The electrical and mechanical characteristics of the electrohydrodynamics flow generated by the discharge are presented and validated by comparing with the experimental data, proving satisfactory accuracy of the model.

Parametric optimization of surface dielectric barrier discharge actuators for ice sensing application

In this paper a parametric optimization of the dielectric barrier discharge (DBD) plasma actuator is conducted in order to achieve better ice sensing and deicing performance. For this purpose, different DBD plasma actuators were tested by changing the main geometrical dimension of the DBD plasma actuator and dielectric material. Both the ice sensing and thermal characteristics of the DBD plasma actuator were analyzed and compared. The results reveal that there exists two separate set of optimum parameters that lead to best ice sensing and thermal behavior. For both the sensing and thermal characteristics, the thinnest DBD showed the best performance. Kapton DBD plasma actuator showed the highest surface temperature while PMMA (poly methyl methacrylate) had the best performance for ice sensing. In the end, the deicing performance of a DBD actuator that had in average better thermal and ice sensing performance was tested for deicing an ice layer and a frost layer. The progress of the deicing process and the ice sensing measure on the surface were recorded and analyzed.

The Dielectric Surface Conductivity Effect on the Dielectric Barrier Discharge Actuator Characteristics

The effect of the surface conductivity on the electrical and mechanical characteristics of the surface dielectric barrier discharge actuator has been numerically investigated in this study. Two typical ac-surface dielectric barrier discharge actuators, wire-to-plate and plate-to-plate, have been considered to control airflow alongside a flat dielectric plate. A sinusoidal high voltage of varied frequencies and amplitudes is supplied to the active electrode, and the passive electrode, which is grounded, is encapsulated inside a dielectric plate. Two-species ion transport model, involving generic positive and negative ions, coupled to the electrostatics model is assumed. The electrostatic field is affected by both the space and the surface charges. The surface charge is accumulated due to ion deposition, but its distribution varies due to the surface ohmic conduction. The Navier–Stokes equations for the flow simulation, which include the time-averaged electrohydrodynamic force determined from the discharge model, are solved to analyze the flow field and the boundary layer morphology. The numerical algorithm has been implemented in the COMSOL commercial package. The significance of the dielectric surface conductivity on the discharge behavior and the flow field has been shown. The dielectric surface conductivity behaves nonmonotonically and affects the flow field by altering the electrohydrodynamics force strength, direction, and distribution.

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.

Nanosecond dielectric barrier discharge on a curved surface in atmospheric air: streamer evolution and aerodynamic perturbations

A curved nanosecond-pulsed dielectric barrier discharge actuator is proposed to fit the flexibly complex surface shape of air vehicles. Streamer evolution and aerodynamic perturbations driven by a single-pulse voltage applied on the anode, where the pulse width is 35 ns and the peak voltage is 14 kV, are numerically studied. Continuity equations that consider 15 species and 34 reactions are solved based on the drift–diffusion approximation. The electron temperature is obtained using the local mean energy approximation method. Discharge characteristics during the voltage-rise, plateau and decay stages are discussed, respectively. The streamer is initiated at 2.2 ns. The maximum electric field is progressively located at the head of the streamer, between the electrodes and in the dielectric layer during the three voltage stages, while the maximum value of electron density is settled at the downstream tip of the driven anode. The electron number density at the streamer head increases at the voltage-rise stage, keeps constant during the voltage-plateau stage, decreases at the beginning of the voltage-decay stage and then increases due to the quenching effect of the excited species. Compared with the discharge on a flat surface, the initial discharge propagation velocity is smaller, while it decreases more slowly during the entire applied voltage. The simulated deposited energy matches the analytical solution well. Aerodynamic perturbations are investigated by solving the compressible Navier–Stokes equations. The ambient air is rapidly heated to the maximum temperature of 1883 K within 0.04 μs. The temperature rise remains greater than 1000 K for 0.32 μs and greater than 500 K for 21.6 μs. A ‘semiring-like’ compression wave is formed from the discharge region; the propagation speed decreases as it propagates away from the wall and then converges to 345 m s−1 at 13 μs. High-speed flows are rapidly induced at the beginning, and two vortexes are formed successively due to the interaction between the flow induced by the actuator and the backflow induced by the compression wave.