Plasma Actuator Research Articles

Differential evolution algorithm for performance optimization of the micro plasma actuator as a microelectromechanical system

Dielectric Discharge Barrier (DBD) plasma actuators are considered as one of the best active electro-hydrodynamic control devices, and are considered by many contemporary researchers. Here a simple electrostatic model, which is improved by authors, and uses the Maxwell’s and the Navier–Stokes equations, is proposed for massive optimization computations. This model is used to find the optimum solution for application of a dielectric discharge barrier on a curved surface of a DU25 wind turbine blade airfoil, in a range of 5–18 kV applied voltages, and 0.5 to 13 kHz frequency range. Design variables are selected as the dielectric thickness and material, and thickness and length of the electrodes, and the applied voltage and frequency. The aerodynamic performance, i.e. the lift to drag ratio of the wind turbine blade section is considered as the cost function. A differential evolution optimization algorithm is applied and we have simultaneously found the optimized value of both geometrical and operational parameters. Finally the optimized value at each voltage and frequency are sought, and the optimum aerodynamic performance is derived. The physical effect of each design variable on the aerodynamic performance is discussed. A design relation is proposed to recommend an optimum design for wind turbine applications.

The role of non-equilibrium plasma kinetic effect on GCH4/GOX rocket engine combustion performance

Non-equilibrium plasma has significant chemical kinetic effect and aerodynamic effect, both of which play an important role in the plasma-assisted combustion. In this paper, the numerical study on plasma-assisted combustion in gaseous methane rocket engine is carried out to investigate the impact of kinetic effect on its combustion performance. There are three schemes of plasma excitation via oxygen, methane and both of them in the numerical simulation model. The variations of combustion chamber temperature, pressure, species concentration and special impulse with different dissociation degrees are analysed in three discharge schemes. The results show that non-equilibrium plasma can effectively increase methane burning rate, shorten unburnt area upstream of combustion chamber, and increase the width of combustion zone in shear layer upstream of combustion chamber. And this phenomenon becomes more obvious with the increase of excitation intensity. In addition, more methane and oxygen are added to the combustion process under plasma actuation, and the mole fraction of water is increased in combustion products. The specific impulse of engine is also increased under plasma actuation. At the same degree of dissociation, the combustion-supporting effect of simultaneous discharge of oxygen and methane is significantly greater than that of any component discharge. And in the condition of single component discharge, the combustion-supporting effect of methane is better than that of oxygen.

An experimental study on different plasma actuator layouts for aircraft icing mitigation

An experimental study was conducted to examine the effects of dielectric-barrier-discharge plasma (DBD) actuator layout on the plasma-induced thermal characteristics and evaluate their effectiveness for aircraft icing mitigation. The experimental investigation was performed in the Icing Research Tunnel of Iowa State University (i.e., ISU-IRT) with an airfoil/wing model embedded with an array of DBD plasma actuators around the airfoil leading edge. The plasma actuators were arranged in different layouts (e.g., orientation, number, and width of exposed electrodes) to evaluate their effects on the anti-icing performance under a typical glaze icing condition pertinent to aircraft inflight icing phenomena. While the dynamics ice accretion or anti-icing process over the airfoil surface before and after turning on the plasma actuators was recorded by using a high-resolution imaging system, a high-speed infrared thermal imaging system was used to quantitatively map the temperature distributions over the airfoil surface. The experimental results clearly reveal that, with the same power consumption level, the plasma actuators in streamwise layout would result in higher plasma-induced surface heating and faster runback of the unfrozen water over the airfoil surface, thereby, having a noticeably better anti-icing performance, in comparison to those in spanwise layout. The plasma actuators in streamwise layout were found to not only be able to prevent ice accretion near the airfoil leading edge, but also allow the plasma-induced surface heating to convect further downstream to delay/prevent the runback ice formation near the airfoil trailing edge. A proper combination of the plasma actuation strength and the plasma discharge coverage over the airfoil surface was found to result in the optimum performance for aircraft anti-icing applications.

Effect of forcing the tip-gap of a NACA0065 airfoil using plasma actuators: A proof-of-concept study

A proof-of-concept study is presented to understand the effect of continuous forcing by a dielectric-barrier-discharge (DBD) plasma actuator on the strength of the vortices formed in the tip-gap of a single NACA0065 airfoil. The airfoil was mounted with variable tip gaps in the test-section of a suction-type wind tunnel. Continuous forcing was generated by mounting a straight DBD actuator in the tip gap. The flow field was investigated experimentally by dynamic-pressure measurements, and stereoscopic-particle-image-velocimetry (SPIV). In addition, URANS was performed to investigate the flow field in the tip gap region, where SPIV could not be conducted. The results showed that the effectiveness of forcing decreased with increasing tip-gaps and free-stream velocity. The maximum cancellation of the vortex was observed when the blowing ratio was approximately 0.93, with a tip gap of 0.02c (c=chord) and free stream velocity of 2.7 m/s. Both experimental and numerical results showed that in this particular case, the DBD actuator created a strong reverse flow opposing the direction of tip flow. This reverse flow altered the pressure gradient in the tip gap region and canceled the vortex altogether.

Finding a low cost energy multi-DBD plasma actuator for natural heat transfer enhancement in a vertical duct

Current study is focused on numerically finding an optimal active control system to augment the natural heat transfer through a vertical duct. This control system consists of a multiple set of wall embedded Dielectric-Barrier-Discharge (DBD) plasma actuators, which inherently consume the electric power to push the momentum near their embedded electrodes. On the other hand, in current study which the vertical duct is exposed to a constant heat flux on one side, the enhancement of natural convection by wall momentum pushes cause the upward flow to recirculate through the channel and consequently decelerates the mass flow rate to give higher outflow temperatures. The numerical simulation deals with the effects of variable parameters such as Rayleigh number, number of DBD actuators, and the vertical DBD arrangements. A descriptive enhancement ratio: The ratio of the average Nusselt number affected by plasma actuation to the average Nusselt number without DBD control, is used to evaluate capability of the heat transfer augmentation. The numerical results showed that the enhancement ratio in the presence of the DBD actuator reaches to about 2.75. However, the results briefly show the sensitivity of the heat transfer enhancement to the Number of the actuators and their arrangement. As the main goal and the final step, the overall thermal efficiency (OTE) as a parameter expressed to further clarify the performance of plasma actuator system from the perspective of energy consumption is defined as the rate of the augmented heat transfer by the DBD actuator to the actuation electric power consumption. Also, it can be realized that by increasing the number of DBD actuators from 1 to 4, the La increases, and over 4 it is constant. The results show that the case N = 4 can be a candidate for the optimum design.

Process of AC multichannel gliding arcs discharge in rotational flow

In order to solve the problem of small and asymmetrical plasma area of the gliding arc (GA) in the chemical treatment process, a plasma actuator driven by alternating current (AC) with a frequency of 23.2kHz was designed to multichannel gliding arcs (MGAs) in a rotational air flow at atmospheric pressure. The spatiotemporally resolved discharge characteristics of the MGA, including long-length breakdown, long-term extinction and typical breakdown features, were investigated combining optical and electrical diagnostic methods simultaneously at a flow rate of 250 SLM (standard liter per minute). The response characteristics of MGA under different flow rates were analyzed. On average, the MGA exhibit 48.8% more discharge power compared to traditional single-channel GA under flow rates of 50–250 SLM, which is due to the GAs continual existence at long-length state, representing better stability of the MGA plasma actuators. It was observed that the frequency of typical breakdown and long-term extinction increased as the flow rate accelerated, and the maximum height the GA could reach decreased with the number of channels increasing from 1 to 5, which can be attributed to the power decline of separate channels of GAs at 50 SLM. It was also found that MGA showed a broader plasma distribution of low electron temperature than traditional single-channel GA.

Laser induced fluorescence investigation of the chemical impact of nanosecond repetitively pulsed glow discharges on a laminar methane-air flame

This paper reports on an experimental investigation of the chemical impact of nanosecond repetitively pulsed (NRP) glow discharges on a laminar methane-air flame. The chosen configuration was a lean wall stabilized flame where NRP discharges were generated across the flame front. After careful selection of the excitation lines, planar laser induced fluorescence of OH and CH was conducted. Comparisons between the OH and CH fluorescence of a base flame (without plasma actuation), and those obtained during the steady state and the transient regimes of plasma actuation, were performed. First it is shown that during the steady state regime, the intensity of OH and CH fluorescence in the flame could be increased by up to 40% and 10%, respectively. In addition, the life time of OH fluorescence in the discharge channel was estimated to be between 3 and 4.5 µs. The transient regime at the beginning of plasma actuation showed that the flame began to be affected by the discharges long before OH fluorescence could be detected in the discharge channel, upstream of the flame. After 40 ms of plasma actuation, OH intensity began to increase simultaneously in both the flame and the discharge area. Based on current knowledge of nanosecond discharge chemistry, explanations for these results are proposed.

Drag reduction of 3D bluff body using SDBD plasma actuators

In the current research, a series of different combinations of plasma SDBD actuators mounted on a simplified road vehicle have been experimentally studied to find the optimum position of the actuators for controlling the flow separation and reducing the vehicle form drag. Separation point of the flow over the rear ramp, large trailing vortices of the standard model, and laminar separation bubble (LSB) of the rear ramp leading edge are among the most significant factors to be controlled. The experiments were conducted at Reynolds numbers ranging from 0.55 × 106 to 1.11 × 106 in a subsonic wind tunnel while the pressure distribution over the model and its streamwise force balance were accurately measured. Significant drag reduction due to the use of DBD actuators was observed. As such, for the range of tested Reynolds numbers, a maximum of 25.1% of drag reduction in the vehicle drag coefficient could be achieved. The optimum combinations of activation voltages (6, 9, and 12 kV) and wave frequencies (6, 10, and 14 kHz) for plasma actuators were also found. Furthermore, it was observed that SDBD actuators mounted on the rear ramp of the model had a deeper impact on the vehicle drag coefficient compared to the other actuators.

Simultaneous ice detection and removal based on dielectric barrier discharge actuators

This paper presents a new technique for ice detection using dielectric barrier discharge (DBD) plasma actuator. The DBD ice sensor consists of a pair of electrodes and a test capacitor. Both numerical simulation and experimental studies were conducted. The electrical characteristics of the DBD actuator were measured in the presence of ice. The presence of ice (or water) leads to an increase of the capacitance compared to air and can thus be detected. Dynamic variation of the actuator capacitance and evolution of ice layer melting process was measured. Moreover, multi-DBD actuator was studied for generating icing map on the surface.

Post-stall flow control using a sawtooth plasma actuator in burst mode

Experimentally investigation is conducted on the control of post-stall airfoil aerodynamics using a vortex-generator type plasma actuator (VG-PA), in burst mode (BM) at a Reynolds number Re of 0.77 × 105. The VG-PA has two sawtooth-shaped electrodes that are separated by a dielectric layer and are arranged with opposite saw-teeth pointing at each other, resulting in a spanwise periodic change in electrode gap. The dependence of the lift coefficient CL of a NACA 0015 airfoil on the non-dimensional burst frequency F+ (= fbc/U∞, where c and U∞ are the airfoil chord length and the freestream velocity, respectively) and duty cycle (DC) is investigated systematically; 144 combinations of F+ (= 0.3-9.0) and DC (= 1%-100%) are examined. Under steady actuation (DC=100%), the stall angle-of-attack α is postponed from 13° to 18° and the maximum CL exceeds that of no control by 9%. Given the same applied voltage Va, this α is postponed to 16° under the optimum BM parameters (F+=0.6, DC=5%), but its maximum CL exceeds that of no control by 27.5%. Furthermore, its consumption of power is only 5% of that under the steady actuation. Careful examination of the flow structure generated by the VG-PA as well as the perturbed airfoil wake unveils distinct mechanisms behind the lift enhancement under the steady and BM actuations. While the former depends on the direct injection of large momentum and vorticity, the latter is linked to the spanwise vortices periodically-induced by the VG-PA.

Control of cavity flow with acoustic radiation by an intermittently driven plasma actuator

In a cavity flow with acoustic radiation, self-sustained oscillations are controlled by a continuously or intermittently driven plasma actuator with elongated electrodes in the streamwise direction, which induces spanwise non-uniformity of the incoming boundary layer. To evaluate the control effects, wind tunnel experiments and compressible flow simulations were conducted. As indicated by sound pressure measurements at the fundamental frequency, the sound reduction level afforded by the intermittent control may be higher than that provided by the continuous control, although both have the same power consumption. In particular, the sound reduction was highest at a certain intermittent frequency (i.e., effective frequency) under a constant driving voltage and duty ratio. To clarify the mechanism for the influence of the intermittent frequency on the control effects, the time variation of the incoming boundary layer and cavity flow during the intermittent period was investigated. The oscillations remained weak under the control of the effective intermittent frequency, while the attenuation and amplification of the oscillations were repeated in the actuator-on and actuator-off durations, respectively, under the control of intermittent frequencies lower than the effective frequency. The amplification rate of the oscillations was found to be correlated with the quality factor of the radiated sound without control. The relationship between the effective frequency and characteristic time for this amplification is also discussed in this paper.

Flow Control Effect of Spanwise Distributed Pulsed Arc Discharge Plasma Actuation on Supersonic Compressor Cascade Flow

To achieve efficient control of supersonic compressor cascade flow, a type of spanwise distributed pulsed arc discharge plasma actuation (PADPA) was designed. To simulate the influences of PADPA on the flow field, a phenomenological model was established. Then, the flow control effects of PADPA on supersonic compressor cascade flow were researched numerically. The results show that under low static pressure ratio condition, the compressive wave induced by PADPA reduced the intensity of the passage shock wave, which eventually reduced shock wave loss. It was also found that PADPA produced an adverse pressure gradient (pre-compression effect) around the actuation location, which reduced the strength of the high adverse pressure gradient induced by the passage shock wave. The airflow on both sides of the actuation location was accelerated by PADPA owing to the spanwise distributed layout. Thus, it improved the ability of the boundary layer to resist the effect of the adverse pressure gradient and reduced the separation zone. Consequently, the total pressure loss was reduced by 6.8%. Under high pressure ratio condition, the effect of PADPA on the suction side controlling the large separation of the boundary layer was insignificant. The total pressure loss also increased slightly.

Research progress and outlook of flow control and combustion control using plasma actuation

Research progress and outlook of flow control and combustion control using plasma actuation

Investigation of the Effect of DBD Plasma Actuator Excitation Frequency on Flow Control Around an Aircraft Wing

Yapılan çalışma ile NACA0015 uçak kanadı etrafındaki akışın kontrolünde plazma aktuatörlerinRe=48 000 değerinde sürüm frekansı ve voltajındaki değişmenin kaldırma kuvvetine etkisi incelenmiştir.Bu kapsamda yapılan çalışmalar ile plazmanın oluşturulmasında etkili olan parametrelerin direkt olarakaerodinamik performansa etkisi değerlendirilmiştir. Yapılan incelemede plazma aktüatörler uçakkanadının ön kısmına (x/C=0.1) yerleştirilmiştir. Deneysel çalışmalar kapsamında ise frekans değişimi ileyüksek hücum açılarındaki ayrılan akışın incelemesi yapılmıştır. Literatürdeki çalışmalar göz önünealındığında çalışmaların büyük çoğunluğunun stol açısı ve post stol açıları için yapıldığı görülmektedir.Yapılan deneysel çalışmalarda, belirli bir hücum açısı aralığı için frekansın ve voltajın etkileriincelenmektedir. Yapılan deneysel çalışmalar sonucunda elde edilen bulgulardan özellikle plazmaaktüatörlerin uygulama voltajının kaldırma katsayısına doğrudan oransal etkisi tespit edilmiştir. Diğertaraftan, sürüm frekansının ise belirgin bir ilişkisi tespit edilememiştir. Bu ilişki daha çok doğrusalolmayan bir yapı şeklinde görünmektedir. Bu durum, özellikle çalışmanın bulgular kısmında detaylıolarak incelenmiştir.

Flow field generated by a dielectric barrier discharge plasma actuator in quiescent air at initiation stage

A single Dielectric Barrier Discharge (DBD) plasma actuator driven by Alternating Current (AC) power, capable of inducing a starting vortex and a wall jet in quiescent air, is suited for low-Reynolds-number flow control. However, the starting vortex and the wall jet are usually observed after the plasma actuator has been operated for dozens of and hundreds of cycles of the voltage, respectively. The detail of the induced flow field at the initiation stage of the plasma actuator has rarely been addressed. At the initiation stage, a thin jet that provides the impetus for the entrainment of the induced flow at the beginning of the plasma actuation is first observed by using a high-accuracy phase-lock Schlieren technique and a high-speed Particle Image Velocimetry (PIV) system. This is the initial form of the momentum transfer from the plasma to the fluid. Then, an arched type jet is created by the plasma actuator. In addition, the whole development process of the induced flow field from the starting point of the thin jet to the quasi-steady stage of wall jet is presented for providing a comprehensive understanding of the plasma actuator and proposing a relevant enhancement of the numerical simulation model.

Large eddy simulation of dynamic stall flow control for wind turbine airfoil using plasma actuator

To solve aerodynamic performance deterioration caused by dynamic stall, a large eddy simulation numerical calculation based on dynamic grid and sliding grid technology was conducted and the dynamic flow control mechanism of unsteady pulsed plasma was explored. The results showed that plasma aerodynamic actuators can effectively control the airfoil’s dynamic stall, improve the mean and transient aerodynamic forces, and reduce the negative peak value of the pitch moment and hysteresis loop area. A negative pressure “bulge” appears in the plasma application areas, and the peak suction of the airfoil’s upper surface obviously increases. Two unsteady control parameters, the pulsed frequency and duty cycle, significantly influence the flow control. When the dimensionless pulsed frequency is 1.5, plasma control improves, and when the duty cycle is 0.8, it is close to the aerodynamic benefits under the continuous working mode. In the deep stall state, plasma impels the flow separation position to obviously move backward, resisting large-scale dynamic stall vortices. The structure of the separation vortices is broken, dissipated, and reattached to the airfoil by the plasma, and the influence area of the vortices is reduced. In the light stall state, the plasma actuator easily controls the shear layer, inducing the transition of the airfoil’s boundary layer and promoting the momentum mixing with the main flow. “Vortex clusters” near the airfoil’s leading edge induced by plasma actuation play a role in the virtual aerodynamic shape. The harmonic oscillation of aerodynamic force/moment is caused by the nonlinear and strong coupling effect between dynamic vortex structures with different scales and frequencies and plasma aerodynamic actuation. The amplitude of low-order mode energy concentration is relatively large, which is mainly caused by the pitching motion. The high-order fluctuation energy concentration is caused by the evolution process of starting vortices and derived secondary vortices with different frequencies induced by plasma.

Plasma actuation for leading edge separation control on 300-kW rotor blades with chord length around 1 m at a Reynolds number around 1.6 × 106

The second field test of a plasma-assisted 300-kW wind turbine was performed to investigate the flow-control authority of plasma-actuation technology at Reynolds numbers (Re) exceeding 106. The turbine rotational speed was regulated via pitch activation in the power-saving operation mode to limit Re to approximately 106. Additional generator-torque control was adopted to make the angles of attack exceed those allowable via original control. The leading-edge plasma electrode was activated at 10-min intervals and turbine characteristics with and without plasma actuation were compared using 1-min-averaged SCADA data, including wind conditions measured by a nacelle anemometer, obtained during a 6-day test. Results of this study reveal that the tip speed ratio (TSR) reduces under high-wind-speed conditions owing to additional torque control. Further, the power coefficient drops in the low TSR operating range, and improves upon plasma actuation. This has been statistically proven for at least one TSR bin. This result implies the existence of leading-edge separation under the additional torque control, and that plasma-actuation technology can effectively control the flow in the 1.6–1.8 × 106 Re range. Results of this study demonstrate the potential of and need for further investigation of the proposed technology to facilitate its application for multi-megawatt wind-turbine.

On the receptivity of surface plasma actuation in high-speed boundary layers

Significant amounts of work have been conducted in the area of plasma flow control, while the receptivity of plasma actuation in high-speed boundary layers has not had much attention over the last two decades. In the present study, the receptivity of a Mach 4.5 flat-plate boundary layer to plasma heating actuation produced by pulsed-DC surface dielectric barrier discharge (SDBD) has been studied by direct numerical simulation (DNS) and stability analysis. With the help of multimode decomposition technology, the amplitude of normal modes can be obtained. The results show that both fast and slow modes can be excited by plasma actuation, and the receptivity maximum is observed near the lower neutral branch. Because the pulsed-DC SDBD actuation is typical periodic pulse signals, when the total power remains constant, the Fourier components with multiples of actuation frequency have the same energy, regardless of the waveform, period, and width of the actuation signal. Such characteristics benefit the robustness of the pulsed-DC SDBD actuator. A theoretical prediction method by combining the receptivity model and linear parabolized stability equations is considered in the present study, and good agreement with the DNS results is achieved.

Hypersonic flow control of shock wave/turbulent boundary layer interactions using magnetohydrodynamic plasma actuators

The effect of magnetohydrodynamic (MHD) plasma actuators on the control of hypersonic shock wave/turbulent boundary layer interactions is investigated here using Reynolds-averaged Navier-Stokes calculations with low magnetic Reynolds number approximation. A Mach 5 oblique shock/turbulent boundary layer interaction was adopted as the basic configuration in this numerical study in order to assess the effects of flow control using different combinations of magnetic field and plasma. Results show that just the thermal effect of plasma under experimental actuator parameters has no significant impact on the flow field and can therefore be neglected. On the basis of the relative position of control area and separation point, MHD control can be divided into four types and so effects and mechanisms might be different. Amongst these, D-type control leads to the largest reduction in separation length using magnetically-accelerated plasma inside an isobaric dead-air region. A novel parameter for predicting the shock wave/turbulent boundary layer interaction control based on Lorentz force acceleration is then proposed and the controllability of MHD plasma actuators under different MHD interaction parameters is studied. The results of this study will be insightful for the further design of MHD control in hypersonic vehicle inlets.

Application of flow control using plasma actuator to horizontal axis wind turbine

In this study, the clarification of the effect of plasma flow control on the rotor performance was carried out as a wind turbine control technology. The flow fields around rotor and the loads acting on wind turbine were measured by wind tunnel test using a test wind turbine with plasma actuator. As a result, in the low tip speed ratio, the power coefficient of Plasma On is larger than that of Plasma Off and the thrust coefficient of Plasma On slightly increased. In particular, the remarkable increase in the power coefficient was 24% at the most effective tip speed ratio. The wind turbine thrust increased slightly in the low tip speed ratio regime, but was less affected by the plasma flow control. In addition, when the power coefficient and thrust coefficient were calculated using the velocity components of the flow field around the wind turbine, the same tendency as in the wind turbine performance test was shown.