Nanosecond Dielectric Barrier Discharge Research Articles

Experimental study on multi-point ignition of NH3/air by high-frequency nanosecond dielectric barrier discharge

Non-equilibrium plasma ignition technology, with its ability to expand ignition limits and increase ignition volume, is considered an important development direction of advanced ignition systems, and has significant advantages in improving ignition stability and combustion rate. This study investigates the ignition and combustion assistance effect of high-frequency nanosecond surface dielectric barrier discharge (nSDBD) on NH3/air mixture in a constant volume combustion chamber (CVCC). The study reveals the influence of high-frequency nSDBD on the growth process of the flame kernel in NH3/air mixture. As the discharge pulse number (PN) increases, the flame kernel develops from the middle position of the discharge filament to the head of the discharge filament, while there is no obvious flame at the root and middle of the discharge filament. Continuous discharge causes the flame kernel to appear concave and the center of the flame kernel to shift towards the wall of the CVCC. In the NH3/air mixture, the initial flame kernels exhibit dissipation phenomenon, resulting in a discrepancy between the number of initial flame kernels and the number of stable combustion flame kernels. As the discharge frequency or pulse number increases, and the number of stable combustion flame kernel increases. The adjustment of discharge frequency and pulse number can effectively control the flame development time (FDT) and flame rise time (FRT) of NH3/air mixture. As PN increases, both FDT and FRT are shortened. When discharge frequency is 20 kHz, the maximum shortening of FDT and FRT are 30 ms and 14 ms, respectively, about 55 % and 30 %. The effects of discharge frequency on FDT and FRT exhibit a non-monotonic variation pattern, and it is necessary to comprehensively consider various discharge parameters to achieve the best ignition effect. The ignition success rate curve of high-frequency nSDBD in NH3/air mixture is steep. The study results of this paper provide new discoveries and experimental data for advanced ignition systems.

Characterization of heated volume generation by nanosecond pulsed plasma actuator with various pressure environments

Nanosecond dielectric barrier discharge (NS-DBD) has emerged as a promising technique for controlling high-speed flows, generating a heated volume that generates strong density and viscosity gradients, thereby perturbing flow dynamics. Since its potential application in low-pressure, high-speed flows, understanding how the size and growth of the heated volume correlate with surrounding pressure is crucial. In this study, we employed typical schlieren and background-oriented schlieren (BOS) techniques to investigate the heated volume’s sensitivity to surrounding pressure in quiescent air. The observed heated volume’s size variations with surrounding pressure likely stemmed from the increase in thermal diffusivity at lower pressures. BOS findings unveiled a nearly linear decrease in heated volume’s core density with energy input. Meanwhile, the heated volume’s size augmented with energy input but exhibited gradual saturation, attributable possibly to shear stresses impeding volume expansion as temperature and viscosity rose, or to consumption of energy in vibration excitation and other reactions. In the cases of 100 and 50 kPa, the sensitivity of the heated volume’s size to the reduced electric field appeared to be similar. However, at 10 kPa, where the reduced electric field is higher compared to that of the 100 and 50 kPa cases due to the lower air density, the size sensitivity drastically decreased. This suggested a transition in discharge mode from filamentary to diffusive behavior at lower pressures.

Numerical study on the periodic control of supersonic compression corner flow using a nanosecond pulsed plasma actuator

This study investigates the effectiveness of a pulsed nanosecond dielectric barrier discharge (NSDBD) plasma actuator for flow control over a supersonic compression corner through numerical simulations. The effects of varying applied voltages, repetitive frequencies, and activated locations of the plasma actuator are examined under large-scale laminar flow separation conditions around a compression corner. The unit Reynolds number and Mach number are 7.8 × 106 m−1 and 4, respectively. The results indicate that the discharge induces a pressure rise and leads to misalignment between the pressure gradient and density gradient in the residual heat region. Because of the interaction between the supersonic freestream and the actuation-induced shock/compression flow, convection, compressibility of the fluid element, and baroclinicity of the residual heat region collectively lead to the formation of an induced spanwise vortex, which in turn enables momentum migration. The induced vortex disrupts the initial flow structures and entrains high-energy fluid from the main flow into the boundary layer, promoting momentum mixing between the main flow and the separated flow, which increases the energy of the boundary layer to resist the adverse pressure gradient. The time-averaged flow structures imply that it is possible to totally eliminate the flow separation near the supersonic compression corner. For aerodynamics on the surface, the normal force produces a pitching moment that can be potentially utilized to control the body's orientation and trajectory. Additionally, total drag on the surface can be reduced by 5 %. This suggests that choosing the most appropriate position based on its local fluid characteristics can strongly increase the control effectiveness.

Effect of Plasma-Enhanced Low-Temperature Chemistry on Deflagration-to-Detonation Transition in a Microchannel

This study examines low-temperature chemistry (LTC) enhancement by nanosecond dielectric barrier discharge (ns-DBD) plasma on a dimethyl ether (DME)/oxygen (Ar) premixture for deflagration-to-detonation transition (DDT) in a microchannel. It is found that non-equilibrium plasma generates active species and kinetically accelerates LTC of DME and DDT. In situ laser diagnostics and computational modeling examine the influence of the ns-DBDs on the LTC of DME and DDT using formaldehyde () laser-induced fluorescence (LIF) and high-speed imaging. Firstly, high-speed imaging in combination with LIF is used to trace the presence of LTC throughout the flame front propagation and DDT. Then, competition between plasma-enhanced LTC of ignition and reduced heat release rate of combustion due to plasma-assisted partial fuel oxidation is studied with LIF. Observations of plasma-enhanced LTC effects on DDT are interpreted with the aid of detailed kinetic simulations. The results show that an appropriate number of ns-DBDs enhances LTC of DME and increases formation and low-temperature ignition, accelerating DDT. Moreover, it is found that, with many ns-DBDs, concentration decreases, indicating that excessive discharges may accelerate fuel oxidation in the premixture, reducing heat release and weakening shock–ignition coupling, inhibiting DDT.

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.

Suppression of coherent interference to electric-field-induced second-harmonic (E-FISH) signals for the measurement of electric field in mesoscale confined geometries.

We present spatially enhanced electric-field-induced second-harmonic (SEEFISH) generation with a chirped femtosecond beam for measurements of electric field in mesoscale confined geometries subject to destructive spurious second-harmonic generation (SHG). Spurious SHG is shown to interfere with the measured E-FISH signal coherently, and thus simple background subtraction is not sufficient for single-beam E-FISH approaches, especially in a confined system with a large surface-to-volume ratio. The results show that a chirped femtosecond beam is effective in preventing higher-order mixing and white light generation in windows near the beam focal point which further contaminates the SEEFISH signal. The successful measurements of electric field of a nanosecond dielectric barrier discharge in a test cell demonstrated that spurious SHG detected with a congruent traditional E-FISH approach can be eliminated using the SEEFISH approach.

Analysis of the efficiency of MHD cycle supported by nanosecond pulsed discharge pre-ionization

A numerical analysis of plasma generation by a nanosecond pulsed discharge in a strong magnetic field was performed. A 2D model of the plasma formation and decay in magnetohydrodynamic (MHD) channel has been elaborated. A comparison with experimental results demonstrates good agreement between calculated and measured plasma distribution in the channel. Preliminary analysis of the efficiency of the MHD-generator based on the nanosecond dielectric barrier discharge flow pre-ionization shows that the ratio of the power required to maintain ionization in the flow to the power extracted from the flow in MHD process is ∼3% for an ideal Faraday MHD generator with segmented electrodes with BY ∼ 5 T and supersonic flow speed uZ ∼ 1600 m s−1. Such a high energy efficiency of the generator allows us to consider this concept of the generator as promising for energy generation and flow control.

Plasma-assisted deflagration to detonation transition in a microchannel with fast-frame imaging and hybrid fs/ps coherent anti-Stokes Raman scattering measurements

This study examines kinetic enhancement by nanosecond dielectric barrier discharge (ns-DBD) plasma on fuel-lean, Φ = 0.7, dimethyl ether (DME), oxygen (O2), and argon (Ar) premixture during deflagration to detonation transition (DDT) experiments in a microchannel. Nonequilibrium plasma produces active species and radicals as well as fast and slow heating of a mixture to promote ignition due to energetic electrons, ions, and electronic and vibrational excitations. Experiments are conducted to examine the influence of the plasma discharge on the premixture and on the resultant deflagration to detonation transition (DDT) onset time and distance through the use of high-speed imaging and one-dimensional, two-beam, femtosecond/picosecond, coherent anti-Stokes Raman scattering (CARS). A high-speed camera is used to trace the time histories of flame front position and velocity and to identify the dynamics and onset of DDT. The results show that plasma discharge can nonlinearly affect the onset time and distance of DDT. It is shown that a small number of plasma discharge pulses prior to ignition result in reduced DDT onset time and distance by 60% and 40%, respectively, when compared to the results without pre-excitation by ns discharges. The results also show that an increase of number of the plasma discharge pulses results in an extended DDT onset time and distance of 224% and 94%, respectively. Time history of the deflagration wave speed of DME and the analysis of ignition timescale under the choking condition of the burned gas of the deflagration wave suggest low temperature ignition may play a role for DME near the isobaric choking condition of the burned gas and the DDT. Plasma-induced low temperature oxidation of the reactive mixture is assessed via the CO2 to O2 ratio as measured through fs/ps CARS during the gas excitation in discharges. CARS measurements also confirm negligible vibrational and rotational heating of the gas by discharge. The present experiments demonstrate the ability of nonequilibrium plasma to alter the chemistry of DME/O2/Ar premixtures in order to control DDT for applications in advanced propulsion engines.

Thermal effects on the performance of a nanosecond dielectric barrier discharge plasma actuator at low air pressure

The thermal effects of a pulsed nanosecond dielectric barrier discharge plasma actuator (NSDBD) with varying pulse voltages and pulse repetitive frequencies under different air pressures ranging from 0.1 to 1 bar are studied experimentally. By observing discharge features with a charge-coupled device camera, the transition from a filamentary discharge mode to a diffuse mode with decreasing air pressure is described. The filamentary streamers extend along the radius direction, forming a thicker yet more stable and uniform plasma region due to the increasing ionized volume yielded by the decreasing air pressure to maintain the high values of the reduced electric field. The spatiotemporal temperature distribution on the surface is captured by an infrared camera, indicating that the heated surface can be divided into three typical regions with different features. Because gas heating is generated in the quenching process of excited molecules, the maximum temperature increase on the surface occurs in the plasma region and attenuates downstream. The surface temperature increase is primarily caused by heat convection from the residual heat in plasma and the heat generated by the dielectric losses. The results of heat flux on the surface suggest that the rising applied voltage may not increase the heat flux in a moderate air pressure ranging from 0.6 to 0.8 bar. Different discharge modes and discharge parameters exhibit markedly different thermal performances. Also, the Schlieren technique and the pressure sensor are used to visualize the induced shock wave, estimate the thermal expansion region, and measure the overpressure strength. The results of the overpressure strength at different air pressures are similar to the thermal features, which highlights the strong influence of the discharge mode on the thermal effect of NSDBD plasma actuators.

Investigation of flow separation control over airfoil using nanosecond pulsed plasma actuator

A detailed investigation of flow separation control over a stalled NACA 0015 airfoil model using pulsed nanosecond dielectric barrier discharge (NS-DBD) plasma actuator is conducted through combined large eddy simulation (LES), dynamic mode decomposition (DMD) and experimental particle image velocimetry (PIV) measurement possibly for the first time. Airfoil flow at chord-based Reynolds number (Re) of Re = 6.3 × 104 is considered. It is found that the interplay of the residual heat due to the nanosecond plasma discharge with external flow causes the generation of vortices through the baroclinic and vortex dilation mechanisms and finally promotes the formation of large-scale vortical structures that dominate the early-stage evolution of the flow control process. One of the most important findings of this work is that the flow control mechanisms are not universal but depend on the forcing frequencies of plasma actuation, and are categorized into three different types. Meanwhile, three-dimensional DMD analysis of LES datasets is performed and the output of modal analysis helps provide more physical insights into flow control and determine the optimum forcing frequency. Depending on the value of forcing frequency, the global or local resonance of the forced flow with the periodic plasma actuation occurs. The plasma forcing at any frequencies in the range 1≤F+≤20 produces pronounced flow control authority except for that at F+=20. Moreover, the optimum forcing frequency is identified and its relationship with the inherent characteristic frequencies of the baseline flow is established based on DMD analysis. It is found that the most favorable control effect is achieved when the plasma excitation frequency is high and very close to the characteristic frequency of the separated shear layer in the unforced baseline flow.

Examination of OH and H2O2 production by uniform and non-uniform modes of dielectric barrier discharge in He/air mixture

In this work we have carried out a parametrical study of hydroxyl radical (OH) generation in nanosecond dielectric barrier discharge (DBD) in He/air mixture using a laser-induced fluorescence approach. The foci of the study are the investigation of differences between uniform and non-uniform modes of the discharges and the difference in production of OH and H2O2 Nanosecond-time scale imaging of the discharge shows transition from streamer to diffuse mode when applied electric field to the discharge gap approaches ∼90 kV cm−1. The results show that both OH production in the gas phase and downstream H2O2 delivery rates to liquid depend on the discharge mode operation and are respectively 30% and 3 times higher for the non-uniform DBD compared to the diffuse discharge.

Advances in Pulsed Power Mineral Processing Technologies

In Russia and globally, pulsed power technologies have been proposed based on the conversion of energy into a short-pulsed form and exposing geomaterials (minerals, rocks, and ores) to strictly dosed high-power pulsed electric and magnetic fields, beams of charged particles, microwave radiation, neutrons and X-ray quanta, and low-temperature plasma flows. Such pulsed energy impacts are promising methods for the pretreatment of refractory mineral feeds (refractory ores and concentration products) to increase the disintegration, softening, and liberation performance of finely disseminated mineral complexes, as well as the contrast between the physicochemical and process properties of mineral components. In this paper, we briefly review the scientific foundations of the effect of both high-power nanosecond electromagnetic pulses (HPEMP) and dielectric barrier discharge (DBD) in air on semiconductor ore minerals (sulfides, rare metals minerals) and rock-forming dielectric minerals. The underlying mechanisms of mineral intergrowth disintegration and changes in the structural and chemical states of the mineral surface when exposed to HPEMP and DBD irradiation are discussed. The high performance and potential limitations of pulsed energy impact and low-temperature plasma produced by DBD treatment of geomaterials are discussed in terms of the directional change in the process properties of the minerals to improve the concentration performance of refractory minerals and ores.

Numerical Study of Stream-wise and Span-wise Nanosecond DBD Plasma Actuators Effects on Supersonic Flow Separation

The current paper aimed to investigate the primary control mechanism of various Nanosecond Dielectric Barrier Discharge (NS-DBD) plasma actuators on the Shock Wave/Boundary Layer Interaction (SWBLI). For this purpose, the effects of the NS-DBD actuator have been investigated on an M=2.8 supersonic flow numerically. The Reynolds Averaged Navier-Stokes (RANS) equations and SST turbulence model were used as the governing equations to simulate the supersonic flow characteristics. The numerical simulation of the baseline flow (without plasma actuator) was verified using an investigation on wall pressure distribution and the size of SWBLI. Then, NS-DBD phenomenological model based on the energy deposition model in accordance with experimental data was applied to the baseline simulation. Moreover, various stream-wise and span-wise NS-DBD plasma actuator models were used to investigate the actuator effects on the studied flow’s low-density separation zone. Comparing the numerical results of the stream-wise and span-wise actuations revealed that both actuator types cause a momentum transferred to the flow, consequently decreasing the SWBLI region’s size and the boundary layer’s thickness. The results showed that the presence of the NS-DBD actuator increased the local temperature of flow over the insulated electrode. In this regard, a stream-wise NS-DBD actuator with a length of 90 mm upstream of the SWBLI increased the separation flow velocity by 33.7% and decreased the length of the separation region by 5 mm. Also, in this case, after 170 microseconds from the start of actuation, the size of SWBLI decreased by 4.2 mm. Therefore, it can be concluded that the stream-wise type of actuation was more effective in reducing the flow separation and SWBLI size than the span-wise type due to vortex generation into the inlet flow and suppressing the SWBLI region. The proposed NS-DBD actuators were mainly capable of applying the momentum to the boundary layer and reducing the velocity of separated flow in the SWBLI zone. The micro shock wave propagation through the flow associated with the NS-DBD discharge of the actuators can produce more effective high-speed flow control.

Control of supersonic compression corner flow using a plasma actuator

The control performance of a pulsed nanosecond dielectric barrier discharge (NSDBD) plasma actuator with varying pulse voltages and locations on a supersonic compression corner is studied using experiments and numerical simulations. The compression corner with a flat plate length of 60 mm and a ramp angle of 10° under laminar flow separation is experimentally investigated in a Ludwieg wind tunnel under a unit Reynolds number of 7.8 × 106 m−1 and Mach number of 4. The plasma actuators are placed either upstream or downstream of the separation point, extending in the spanwise direction. The Schlieren technique is used to visualize the shock wave interaction and estimate the propagation speed of the induced shock by the plasma actuator. For the numerical simulations, a one-zone inhomogeneous phenomenological plasma model is adopted to predict key discharge parameters and simulate the fast-heating region. The results show that the reduction of separation bubble length is up to 17% and 45%, respectively, in the cases of upstream and downstream of the separation point under a high applied voltage of 50 kV. The evolution of the flow structures is examined to reveal the underlying control mechanism. The results indicate that the high-speed external fluid is entrained into the original separation region after NSDBD activation upstream of the separation point, resulting in flow reattachment upstream of the corner. The entrained fluid with high momentum compels the main separation to move downstream, accompanied by the fragmentation of the original shear layer. Furthermore, the suppression of the separation region is more effective when the plasma actuator is installed close to the separation region and in the first 200 μs during one pulse, providing a good suggestion for the actuation frequency and installed location.

Electrical Parameters of Nanosecond Dielectric Barrier Discharges (nsDBD)

In this study, an electrical device is proposed to generate plasmas in the nanosecond dielectric barrier discharge (nsDBD) configuration and to measure the electrical parameters of the discharge over a large bandwidth. Electrical parameters were experimentally determined using a common dielectric barrier discharge equivalent circuit extended here to high frequencies. An efficient synchronization procedure based on a comparison to circuit simulation results was proposed. Discharge current pulses with rise times less than 1 ns and amplitudes up to 50 A were measured. The energy deposited into the plasma and the discharge resistance were determined as a function of time. In addition, circuit simulations support the experimental approach. The nsDBD was accurately modeled by a resistance of the plasma channel following a Rompe and Weizel law in series with resistance for the discharge spreading along the dielectric surface and a sheath capacitance.

Supersonic compressor cascade flow control using plasma actuation at low Reynolds number

To control the supersonic compressor cascade flow at low Reynolds numbers, this paper describes the use of nanosecond dielectric barrier discharge (NS-DBD) plasma actuation for flow control, and presents the results of large-eddy simulations conducted to investigate the corresponding flow control effects. NS-DBD plasma actuation on both the blade pressure surface and suction surface induces a distorted flow structure (DFS) within the blade passage. In the case of NS-DBD plasma actuation on the blade pressure surface, the influence of the DFS on the flow is suppressed by a shock wave. Even so, the DFS can still trigger the instability in the shear layer between the separated flow and the mainstream flow. Shock-wave-induced large-scale flow separation on the blade pressure surface is then suppressed, and the overall total pressure loss of the blade passage is reduced by 7.4%, despite the increased shock wave loss from the reduced flow blockage within the blade passage. In the case of NS-DBD plasma actuation on the blade suction surface, the DFS is less effective in suppressing the shock-wave-induced small-scale flow separation on the blade suction surface. However, the DFS on the blade suction surface enhances the shock wave oscillations within the blade passage, and this suppresses the flow separation on the blade pressure surface.

Comparative study on high-voltage nanosecond pulses and dielectric barrier discharge effects on surface morphology and physico-chemical properties of natural pyrrhotite

In this paper we used analytical electron microscopy, potentiometric titration (electrode potential), sorption and flotation measurements and other methods to study changes in the surface morphology, electrochemical, and physicochemical properties of the natural pyrrhotite exposed to nonthermal action of the repetitive nanosecond high-power electromagnetic pulses and low-temperature plasma of dielectric barrier discharge in air at atmospheric pressure. As a result of exposure to high-voltage nanosecond pulses, a sharp shift in the electrode potential of pyrrhotite to the region of negative values caused a decrease in the sorption of the anionic collector on the mineral, a decrease in the hydrophobicity of the surface and flotation of the mineral was due to an increase in the content of oxidized ferric iron on the mineral surface. Dielectric barrier discharge treatment caused the shift of the electrode potential to the region of negative values (–60 mV) in the range of pH 9.7-12, which causes the effect of a decrease in the sorption and flotation activity of pyrrhotite. The advantages of using the short-term (10-30 seconds) energy impacts for structural and chemical modification of the surface and physicochemical properties of sulfide minerals of iron are shown.

Effects of massive electromagnetic pulses on the structural and chemical properties and leaching efficiency of eudialyte concentrate

Scanning electron microscopy (SEM) and infrared spectroscopy (IR) were used to study the influence of high-power nanosecond electromagnetic pulses (HPEMP) and dielectric barrier discharges (DBD) in air at the atmospheric pressure on the structural and chemical properties of eudialyte. The spectral data analysis has shown that highintensity electric fields initiate mineral surface fracturing due to the weakening and/or breaking of bonds in the structural fragments of the mineral framework (presumably, Si10O27, and Si9MO30). According to the SEM data, HPEMPs cause sample surface strength reduction with the formation of new surface reliefs in the range from parallel (texp = 30 s) to polygonal fractured shapes (texp = 60 and 90 s), depending on the electromagnetic pulse exposure time texp. Eudialyte grain micromorphology after the treatment under DBD conditions is distinctively characterized by the presence of imprints of electrical current breakdown microchannels of up to 3–4 μm, with practically no microcracks or other defects occurring on the mineral surface. The intensifying effect of high-power electromagnetic pulses on the process of eudialyte concentrate acid leaching has been experimentally established. Zirconium recovery into the pregnant solution is improved by 3.4 to 4.3 % through HPEMP pretreatment and by 4.0 % through DBD exposure, with the total recovery of rare earth elements increasing by 1.1 to 1.7 %.This work was financially supported by the Ministry of Science and Higher Education of the Russian Federation, project No. 13.1902.21.0018 (agreement No. 075-15-2020-802).

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.

Compressor Airfoil Separation Control Using Nanosecond Plasma Actuation at Low Reynolds Number

Flow control effects of three types of nanosecond (NS) dielectric barrier discharge (DBD) plasma actuations in suppressing the flow separation of a compressor airfoil at low Reynolds number are investigated using large-Eddy simulation. It has been found that the NS DBD plasma actuation can effectively suppress the flow separation and two mechanisms behind the flow control effect have been uncovered. First, the NS DBD plasma actuation can induce distorted flow structure (DFS) within the flowfield, and the induced DFS of plasma actuations located upstream of the flow separation zone can bring the Kelvin–Helmholtz instability of the shear layer between mainstream flow and separated flow froward to the separation point. Then, a large-scale spanwise vortex, which promotes the mixing of the main flow and the separated flow, is induced within the flow separation zone, thus resulting in suppression of the flow separation. Second, the plasma actuation located at the blade leading edge can improve the momentum of the laminar boundary layer, owing to the propagations of compressive waves as well as DFS along the blade surface. The plasma actuation located within the separation zone fails to suppress the boundary-layer flow separation effectively because the induced DFS cannot influence the shear layer between mainstream flow and separated flow.