Nanosecond Pulsed Plasma Actuator Research Articles

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.

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.

Characteristics of a nanosecond pulsed dielectric barrier plasma actuator with a surface water film

Aircraft icing is one of the most serious hazards for airflight operations. The nanosecond pulsed surface dielectric barrier discharge (NSDBD) plasma actuator is recognized as an extremely promising anti-icing technology. In this paper, a multi-physics coupling simulation is used to study the plasma-discharge characteristics and responses of the air–water flow field generated by an NSDBD plasma actuator with a surface water film. The computational model describes air flows through an NSDBD plasma actuator with a water film at the center of two upper powered electrodes. The multi-physics model is solved using the drift-diffusion and energy-conservation equations for the plasma discharge and the mass, momentum, energy, and concentration equations for the air–water flow. The results show that, at the beginning of the voltage pulse, the surface water film has no effect on the plasma discharge. Then, during the pulse plateau time, the film leads to a longer plasma-discharge time and a larger plasma-discharge region. Furthermore, the film causes the plasma-actuator surface to develop a virtual positive electrode that would otherwise be absent and results in the plasma actuator generating more intense shock waves, higher gas temperatures, and larger heated regions.

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

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

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

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

Flow-Control Characteristics with Nanosecond-Pulse Plasma Actuator for Different Airfoil Shapes

The wind tunnel experiments of separation flow control by a nanosecond-pulse-driven dielectric-barrier-discharge plasma actuator (ns-DBDPA) for three airfoil shapes of NASA-Common-Research-Model (NASA-CRM), Gottingen387, and NACA0015 airfoils were conducted and the results were compared. Aerodynamic forces, surface pressures, and particle image velocimetry images were obtained in the experiments. The results of the aerodynamic force and surface pressure measurements showed that the characteristics of the flow separation control by ns-DBDPA are clearly different depending on the airfoil shape, and particularly the type of stall. NACA0015 exhibited leading-edge stall under the conditions investigated, and ns-DBDPA achieved flow control by producing vortices. NASA-CRM exhibited thin-airfoil stall, and ns-DBDPA increased the maximum lift of the lift curve even after the stall. On the other hand, Gottingen387, which exhibited trailing-edge stall, achieved almost no flow control at any actuator position, actuation frequency, or voltage amplitude. The flow control mechanisms for different types of airfoils are discussed based on the particle image velocimetry measurement results.

Characterization of the single nanosecond pulsed surface dielectric barrier plasma actuator: Geometric and electric effects

AbstractThe influence of the electrode length and the voltage pulses on the discharge characteristics of the surface dielectric barrier discharge actuators were investigated numerically by using the plasma kinetic model. The governing equations including the coupled continuity plasma discharge equation, drift‐diffusion equation, electron energy equation, Poisson's equation, and Navier–Stokes equation were solved in quiescent air at atmospheric pressure. The results show that the shorter pulse rising time results in higher discharge characteristics, more intense discharge, and bigger discharge region. Differently, the compared discharge characteristics for the electrodes with different lengths prove that the length of the powered and ground electrodes has little effect on the surface dielectric barrier discharge driven by nanosecond pulsed voltage.

A Numerical RANS‐Based Model of a Nanosecond Pulsed Plasma Actuator for Flow Control over an Airfoil

AbstractAirfoil stall influences the performance of flight vehicles and remains a challenge for the design of modern aircraft. A Dielectric Barrier Discharge (DBD) device seems to be a promising tool to control the flow over various parts of an aircraft and to suppress separation. A phenomenological model based on dynamic similarity is developed to simulate the control effect of a Nanosecond Dielectric Barrier Discharge (NS‐DBD) actuator. A two‐dimensional numerical simulation considers the response of the flow past a NACA 0015 airfoil at 14° post stall angle of attack and a Reynolds number of 250,000 to pulsed surface heating at the leading edge. The RANS‐based numerical results have been obtained for a baseline simulation (no actuation) and an open‐loop control simulation of the airfoil. A one‐equation local correlation‐based transition model is implemented to capture laminar‐turbulent transition. The numerical results of both the baseline and the actuated case are in good agreement with experiments performed by other authors.

Numerical investigation of nanosecond pulsed plasma actuators for control of shock-wave/boundary-layer separation

This study numerically explores the flow physics associated with nanosecond pulsed plasma actuators that are designed to control shock-wave induced boundary-layer separation in a Mach 2.8 supersonic flow. By using two dielectric barrier surface discharge actuator configurations, parallel and canted with respect to the flow velocity vector, a previous experiment suggested that the actuator worked in two ways to influence the interaction: boundary layer heating and vorticity production. The heating effect was enhanced with the parallel electrode and made the boundary-layer separation stronger, while the canted electrode produced vorticity and suppressed the boundary-layer separation due to the momentum transfer from the core flow. Because the detailed physical processes are still unclear, in this paper a numerical investigation is undertaken with a large eddy simulation and an energy deposition model for the plasma actuation, in which the dielectric barrier discharge produced plasma is approximated as a high temperature region. The flow characteristics without the plasma actuation correspond to the experimental observation, indicating that the numerical method successfully resolves the shock-wave/boundary-layer interaction. With the plasma actuation, complete agreement between the experiment and calculation has not been obtained in the size of the shock-wave/boundary-layer interaction region. Nevertheless, as with the experiment, the calculation successfully demonstrates definite difference between the parallel and canted electrodes: the parallel electrode causes excess heating and increases the strength of the interaction, while the canted electrode leads to a reduction of the interaction strength, with a corresponding thinning of the boundary layer due to the momentum transfer. The counter flow created by the canted actuator plays an important role in the vortex generation, transferring momentum to the boundary layer and, consequently, mitigating the shock induced boundary layer separation.

On the boundary flow using pulsed nanosecond DBD plasma actuators

Our previous studies in quiescent air environment [Z. J. Zhao et al., AIAA J. 53(5) (2015) 1336; J. G. Zheng et al., Phys. Fluids 26(3) (2014) 036102] reveal experimentally and numerically that the shock wave generated by the nanosecond pulsed plasma is fundamentally a microblast wave. The shock-induced burst perturbations (overpressure and induced velocity) are found to be restricted to a very narrow region (about 1 mm) behind the shock front and last only for a few microseconds. These results indicate that the pulsed nanosecond dielectric barrier discharge (DBD) plasma actuator has stronger local effects in time and spatial domain. In this paper, we further investigate the effects of pulsed plasma on the boundary layer flow over a flat plate. The present investigation reveals that the nanosecond pulsed plasma actuator generates intense perturbations and tends to promote the laminar boundary over a flat plate to turbulent flow. The heat effect after the pulsed plasma discharge was observed in the external flow, lasting a few milliseconds for a single pulse and reaching a quasi-stable state for multi-pulses.

A note on supersonic flow control with nanosecond plasma actuator

A concept study on supersonic flow control using nanosecond pulsed plasma actuator is conducted by means of numerical simulation. The nanosecond plasma discharge is characterized by the generation of a micro-shock wave in ambient air and a residual heat in the discharge volume arising from the rapid heating of near-surface gas by the quick discharge. The residual heat has been found to be essential for the flow separation control over aerodynamic bodies like airfoil and backward-facing step. In this study, novel experiment is designed to utilize the other flow feature from discharge, i.e., instant shock wave, to control supersonic flow through shock-shock interaction. Both bow shock in front of a blunt body and attached shock anchored at the tip of supersonic projectile are manipulated via the discharged-induced shock wave in an appropriate manner. It is observed that drag on the blunt body is reduced appreciably. Meanwhile, a lateral force on sharp-edged projectile is produced, which can steer the body and give it an effective angle of attack. This opens a promising possibility for extending the applicability of this flow control technique in supersonic flow regime.

Control of Shock-Wave/Boundary-Layer Interaction Using Nanosecond-Pulsed Plasma Actuators

Nanosecond-pulsed surface dielectric barrier discharge plasma actuators are used to control shock-wave/boundary-layer interactions. Characterization of the separation region without plasma actuation is conducted to understand the interaction based on measurements of pressure distribution, schlieren imaging, and velocimetry by the femtosecond laser electronic excitation tagging technique. The results show a weak separation due to the interaction. Three types of plasma actuators are applied to control the separation. Schlieren images are taken by a high-speed camera to evaluate the magnitude of the interaction. It is shown that the plasma actuators affect the flow in two different ways: heat generation in the boundary layer, and generation of vorticity near the surface. When the first effect is dominant, the shock-wave/boundary-layer interaction becomes stronger and the size of the separation bubble increases. If the vorticity generation prevails, it suppresses the separation due to the momentum transfer from the main flow to the boundary layer. The experimental results of the three actuator’s geometries provide the design guidelines for nanosecond-pulse-driven electrodes to control the interaction. An optimal actuation frequency is found through an investigation of the frequency response of the flow.

Nanosecond-Pulsed Dielectric Barrier Discharge Plasma Actuator for Airflow Control Along an NACA0015 Airfoil at High Reynolds Number

The goal of the present experimental study is to investigate the ability of a surface nanosecond pulsed dielectric barrier discharge plasma actuator, located at the leading edge of the airfoil, to delay flow separation along the suction side of an NACA0015 airfoil inclined at 13.5°, using a particle image velocimetry system. The free-stream velocity is equal to U <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> = 40 m/s, giving a chord-based Reynolds number of R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ec</sub> = 1.33×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> . At such conditions, the baseline flow separation occurs at about 50% of chord. On the one hand, the results show that the separation location moves progressively toward the trailing edge when the high-voltage frequency Fpulse is increased, up to 85% of chord at 1630 Hz (reduced frequency F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pulse</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> = 10.6), which is due to the increase of the injected electrical power with F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pulse</sub> (from 8 mW/cm at 40 Hz to 290 mW/cm at 1630 Hz). On the other hand, the use of a burst-modulated actuation (with a constant electrical power consumption equal to 145 mW/cm) does not produce the same behavior. At the lowest and highest frequencies (16 and 408 Hz, corresponding to the reduced frequencies of 0.1 and 2.65, respectively), the separation is delayed to about 60% of chord, while the most effective actuation is observed at F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">burst</sub> = 80 Hz (F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">burst</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> = 0.53) with a separation delaying to 83% of chord.

Induced Velocity and Density Gradients due to Nanosecond Plasma Actuation

An experimental and numerical investigation is presented on the effects due to the energy deposition induced by a nanosecond pulsed dielectric barrier discharge plasma actuator on a flat-plate boundary layer. High magnification rate particle image velocimetry was used in a phase-locked arrangement to resolve the velocity field after actuation. The parameters investigated were the orientation of the actuator with respect to the flow direction and the energy input. The backcurrent shunt technique was employed to monitor the high-voltage pulse and to calculate the energy input. Results indicate that effects induced by this type of plasma actuator are strongly dependent on the orientation of the actuator with respect to the direction of the flow. When the covered high-voltage electrode is in the upstream position, a region of decelerated flow is observed in the vicinity of the actuator. On the other hand, when the covered high-voltage electrode is in downstream position, a region of accelerated flow is observed, highlighting the presence of a weak directional body force in addition to the thermal energy deposition typically associated with nanosecond plasma actuation. The thermal energy deposition is responsible for considerable density gradients, which are calculated using the compressible continuity equation on the measured velocity fields. Calculations show good qualitative agreement with experimental schlieren imaging. In general, nanosecond pulsed dielectric barrier discharge plasma actuators appear to induce a combination of thermal effects manifested as density/viscosity gradients and momentum effects manifested as weak directional body forces.

The study of flow separation control by a nanosecond pulse discharge actuator

The basic dynamic characteristic of a nanosecond (NS) pulse discharge actuator in still air is investigated, which introduces viscid and inviscid effects to the flow, namely, heated air and pressure waves, respectively. The efficacy of a dielectric barrier discharge plasma actuator driven by a nanosecond pulse for active flow separation control is investigated experimentally on a NASA SC(2)-0712 aerofoil at Re=0.5×106 (25m/s). The pressure distribution on the aerofoil surface is measured, and the result indicates that the separation is well controlled at a high angle of attack. The PIV test result shows that the forcing frequency selectively affects the flow over the aerofoil, and a higher forcing frequency has a better influence on the leading edge shear layer. Schlieren imaging experiments at Re=0.1×106 (5m/s) show that the main disturbance factor for the nanosecond pulse plasma actuator is the heating effect, which changes the local temperature and density and induces several vortex structures. The vortex structures entrain the outer high-momentum fluid into the shear layer, thereby strengthening the mixing of the shear layer with the main flow and delaying separation or even reattaching a separated flow. The research reveals the major disturbance factor introduced by NS discharge applied to flow separation control. Furthermore, the spatiotemporal disturbance process induced by the pulse discharge is investigated.

Aerodynamic performance enhancement of a flying wing using nanosecond pulsed DBD plasma actuator

Experimental investigation of aerodynamic control on a 35° swept flying wing by means of nanosecond dielectric barrier discharge (NS-DBD) plasma was carried out at subsonic flow speed of 20–40m/s, corresponding to Reynolds number of 3.1×105–6.2×105. In control condition, the plasma actuator was installed symmetrically on the leading edge of the wing. Lift coefficient, drag coefficient, lift-to-drag ratio and pitching moment coefficient were tested with and without control for a range of angles of attack. The tested results indicate that an increase of 14.5% in maximum lift coefficient, a decrease of 34.2% in drag coefficient, an increase of 22.4% in maximum lift-to-drag ratio and an increase of 2° at stall angle of attack could be achieved compared with the baseline case. The effects of pulsed frequency, amplitude and chord Reynolds number were also investigated. And the results revealed that control efficiency demonstrated strong dependence on pulsed frequency. Moreover, the results of pitching moment coefficient indicated that the breakdown of leading edge vortices could be delayed by plasma actuator at low pulsed frequencies.

Leading-Edge Separation Control Using Alternating-Current and Nanosecond-Pulse Plasma Actuators

Wind-tunnel experiments were conducted to quantify the effectiveness of ac and nanosecond-pulse single dielectric barrier discharge plasma actuators to suppress leading-edge stall on a NASA Energy Efficient Transport airfoil at Mach numbers up to 0.4 and chord Reynolds numbers up to . The airfoil model was designed to have a removable leading edge to accommodate two different leading-edge plasma-actuator designs, either with a thick ceramic or a thin Kapton dielectric layer. The exposed electrode for both plasma actuators was located at the leading edge of the airfoil. The covered electrode for both was on the suction side of the leading edge. The model was mounted on stages that measured the lift and drag forces and the pitching moment about the quarter-chord location. Both steady and unsteady ac plasma-actuator operation were examined. By its nature, the nanosecond-pulse plasma actuator only operates in unsteady operation. The optimal unsteady frequencies with regard to lift, lift to drag, and pitch moment for both actuators were examined. Although operating on different principles, both plasma-actuator approaches were able to increase the maximum lift coefficient and stall angle of attack for the full range of Mach numbers. Mach number scaling of the ac actuator lift enhancement is presented.