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We introduce a fluid computational model for the numerical simulation of atmospheric pressure dielectric barrier discharge plasmas. Ion and neutral species are treated with an explicit drift diffusion approach. The Boltzmann relation is used to compute the spatial distribution of electrons as a function of the electrostatic potential and the ionic charge density. This technique, widely used to speed up particle and fluid models for low-pressure conditions, poses several numerical challenges for high-pressure conditions and large electric field values typical of applications involving atmospheric-pressure plasmas. We develop a robust algorithm to solve the non-linear electrostatic Poisson problem arising from the Boltzmann electron approach under AC electric fields based on a charge-conserving iterative computation of the reference electric potential and electron density. We simulate a volumetric reactor in dry air, comparing the results yielded by the proposed method with those obtained when the drift diffusion approach is used for all charged species, including electrons. We show that the proposed methodology retains most of the physical information provided by the reference modeling approach while granting a substantial advantage in terms of computation time.

Atmospheric-pressure plasma treatments for industrial and biomedical applications are often performed using Dielectric Barrier Discharge reactors. Dedicated power supplies are needed to provide the high voltage frequency waveforms to operate these nonlinear and time-dependent loads. Moreover, there is a growing technical need for reliable and reproducible treatments, which require the discharge parameters to be actively controlled. In this work, we illustrate a low-cost power supply topology based on a push-pull converter. We perform experimental measurements on two different reactor topologies (surface and volumetric), showing that open loop operation of the power supply leads to a temperature and average power increase over time. The temperature increases by Delta T-vol similar to 120 degrees C and Delta T-sup similar to 70 degrees C, while the power increases by Delta P-vol similar to 78% and Delta P-sup similar to 60% for the volumetric (40 s) and superficial reactors (120 s), respectively. We discuss how these changes are often unwanted in practical applications. A simplified circuital model of the power supply-reactor system is used to infer the physical relation between the observed reactor thermal behavior and its electrical characteristics. We then show a control strategy for the power supply voltage to ensure constant average power operation of the device based on real-time power measurements on the high voltage side of the power supply and an empirical expression relating the delivered power to the power supply output voltage. These are performed with an Arduino Due microcontroller unit, also used to control the power supply. In a controlled operation the measured power stays within 5% of the reference value for both configurations, reducing the temperature increments to Delta T-vol similar to 80 degrees C and Delta T-sup similar to 44 degrees C, respectively. The obtained results show that the proposed novel control strategy is capable of following the transient temperature behavior, achieving a constant average power operation and subsequently limiting the reactor thermal stress.

Understanding the production mechanisms of ozone and other reactive species in atmospheric pressure dielectric barrier discharges (DBDs) has become increasingly important for the optimization and commercial success of these plasma devices in emerging applications, such as plasma medicine, plasma agriculture, and plasma catalysis. In many of these applications, input power modulation is exploited as a means to maintain a low gas temperature. Although the chemical pathways leading to ozone production/destruction and their strong temperature dependence are relatively well understood, the effect of the on-time duration on the performance of these modulated DBDs remains largely unexplored. In this study, we use electrical and optical diagnostics, as well as computational methods, to assess the performance of a modulated DBD device. The well-established Lissajous method for measuring the power delivered to the discharge is not suitable for modulated DBDs because the transients generated at the beginning of each pulse become increasingly important in short on-time modulated plasmas. It is shown that for the same input power and modulation duty-cycle, shorter on-time pulses result in significantly enhanced ozone production, despite their operation at slightly higher temperatures. The key underpinning mechanism that causes this counter-intuitive observation is the more efficient net generation rate of ozone during the plasma on-time due to the lower accumulation of NO2 in the discharge volume.

This paper presents recent activities covering different plasma fields, from both theoretical and experimental point of views. An overview of the present interests of the scientific community is reported here. Starting from a brief description of the role of collisions in astrophysical plasmas, some fundamental aspects of gas discharges modelling, such as superelastic collisions and the basic concept of vibrational temperature, are discussed. Different plasma sources, as DBD and microwave discharges with their own specific applications, are reported. Edge plasmas in nuclear fusion reactors are investigated, focusing on the cooling mechanisms resulting from nitrogen puffing in the divertor region. Graphic abstract: [Figure not available: see fulltext.].

This paper has the main purpose to assess the influence of nanofillers on the mobility of electrostatic surface charge buildup. Electro Hydro Dynamic actuators were produced and tested at a fixed voltage amplitude and frequency, using different thermoplastic dielectrics, some of which belonging to the family of nano-filled materials. The investigation focuses on the mobility of superficial electrostatic buildup, also experimenting the validity of an alternative high voltage potential measurement technique based on monitoring of multiple embedded electrodes. Results show that nanofillers have a profound effect on electrostatic charge buildup, strongly reducing their mobility.

Current standards base the evaluation of partial discharge (PD) harmfulness on their amplitude and repetition rate. This work shows how, on the contrary, the non conventional environmental conditions introduced by aerospace applications (i.e. low-pressure atmosphere, higher frequency supplies) lead respectively to lower or unchanged PD apparent charges, which are however characterized by different mean energies, hence destructive potential, in a counter intuitive manner.

In this paper, a multi-stage numerical methodology for the description of the Dielectric Barrier Discharge physics in air is discussed. The behavior of the heavy species is computed using drift-diffusion equations. Electrons are taken into account by solving a non-linear formulation of electrostatics. The physical effects of the steamer discharges are modelled by means of a simplified 0D approach. The model also includes a semi-implicit 0D model for the assessment of the elementary chemical processes occurring in air. The developed methodology is employed for the simulation of a volumetric Dielectric Barrier Discharge reactor. The obtained species number density and surface charge deposition rates and are shown and discussed.

This study presents a novel technique to inactivate coccidian oocysts in an aqueous solution. The technique consists of treating the contaminated liquid by using an atmospher- ic-pressure air dielectric barrier discharge (DBD) plasma in contact with it. Many experiments in several operating conditions were performed. The discharge was supplied by sinusoidal and nanosecond-pulsed voltages with a constant average power of ~7 W in both cases. Biological effects due to the plasma were investigated by performing tests with increasing treatment time. A sudden ~40% drop in the number of survived oocysts was reached in 4 min and a two-fold reduction was detected after 12 min of exposure. No significant differences in the biocidal efficacy were detected between the AC-driven and the nanosecond-pulsed discharge. Chi-squared statistical analysis on the treated samples showed significant statistical difference (with a statistical significance P value parameter less than 0.01) and nonrandomness warranty of the results, opening interesting scenarios for fimire developments.

This paper reports on the effects of a series of fluid-dynamic dielectric barrier discharge plasma actuators on a NACA0015 airfoil at high angle of attack. A set of jet actuators able to produce plasma jets with different directions (vectoring effect) and operated at different on/off duty cycle frequencies are used. The experiments are performed in a wind tunnel facility. The vectorized jet and the transient of the flow induced by unsteady duty cycle operation of each actuator are examined and the effectiveness of the actuator to recover stall condition in the range of Reynolds numbers between 1.0 × 105 and 5.0 × 105 (based on airfoil chord), is investigated. The actuator placed on the leading edge of the airfoil presents the most effective stall recovery. No significant effects can be observed for different orientations of the jet. An increase of the stall recovery is detected when the actuator is operated in unsteady operation mode. Moreover, the frequency of the on/off duty cycle that maximizes the stall recovery is found to be a function of the free stream velocity. This frequency seems to scale with the boundary layer thickness at the position of the actuator. A lift coefficient increase at low free stream velocities appears to linearly depend on the supply voltage.

In this paper a high-voltage sinusoidal power supply controlled by Arduino DUE micro-controller is described. This generator can feed a dielectric barrier discharge (DBD) load with sinusoidal voltages up to 20 kV peak and frequencies in the range 10&ndash, 60 kHz, with a maximum output power of 200 W. Output voltage can be produced either in a continuous mode, or with on/off modulation cycles, according to treatment/application requirements. This power source is equipped with on-board diagnostics used to measure the output voltage and the charge delivered to the load. With a sample frequency of 500 kHz, Arduino DUE allows to evaluate both the high voltage and the average power feeding the discharge without the use of an expensive external measurement setup. Lissajous techniques are utilized to calculate discharge average power in a quasi-real-time manner. When a load is connected to high-voltage terminals, a self-tuning procedure is carried out to obtain the best working frequency. This parameter allows to minimize power-electronic component stress and to maximize generator efficiency.

The main purpose of this work is to evaluate the charge stored in the surface of a volumetric Dielectric Barrier Discharge (DBD) when supplied by a variable voltage waveform. DBD reactors are used in a wide range of industrial applications and can be considered as a model for partial discharges occurring in insulating materials. The knowledge of the amount of charge stored onto the dielectric surface is a key-role parameter to better understand discharge evolution mechanism.

To investigate ozone yield limit in low temperature plasmas, a detailed thermodynamic model is developed to calculate theoretical ozone yield for the first time. Theoretical ozone yield is calculated both from overall reaction and detailed reactions. In the former case, the highest theoretical ozone yield of 1211±2 g kWh−1 is obtained when final gas temperature equals the initial one, and all energy is effectively utilized to synthesize ozone. When final gas temperature is not equal to the initial one, theoretical ozone yield increases with the increase of oxygen admixture ratio and oxygen conversion ratio as well as the decrease of final gas temperature. Theoretical ozone yields are 921.22 g kWh−1 and 487.54 g kWh−1 in pure oxygen and in synthetic air respectively at final gas temperature of 400 K and oxygen conversion ratio of 10%. When detailed reactions and electron energy distribution function is considered, theoretical ozone yield rapidly increases by enhancing reduced field. Oxygen admixture ratio also has non-negligible effects on ozone yield. A higher oxygen admixture ratio leads to higher energy efficiency. The theoretical ozone yields are 238.92 g kWh−1 and 191.14 g kWh−1 in pure oxygen and in synthetic air at reduced field of 300 Td respectively. Graphical abstract: [Figure not available: see fulltext.].

In this study we examine both the effect of changing the applied voltage waveform shape and the modulation on-time on the amount of ozone dissolved within a liquid in a dielectric barrier discharges (DBD) bubble reactor. In this device, the discharge forms at the gas–liquid interface allowing for effective transfer of the plasma effluent into the liquid. To produce different voltage waveforms, a multilevel inverter power supply capable of generating arbitrary waveforms without switching-on and switching-off transients has been used. Of the four waveforms used in the study (sinusoidal, sawtooth, square and short-pulse), the square waveform was found to be the most efficient at producing the highest ozone concentration for a fixed peak voltage and average power. To determine the effect of the modulation on-time, the number of cycles during the on-time were increased from 1 up to 1000, adjusting the off-time accordingly to maintain the same duty cycle. Shorter on-time periods were found to be more efficient. Experimental and computational results indicate that the time between subsequent discharges is critical for increased ozone generation efficacy, as this needs to be long enough for ozone produced in one discharge event to diffuse away from the discharge region before the next discharge event occurs, thereby avoiding its partial destruction in the plasma. This insight provides a valuable criterion for the optimization of DBD reactors used in novel biomedical, agricultural and environmental applications.

Charge particles can increase the biocidal efficacy of nonthermal plasmas in indirect treatments. The aim of this study is to increase the amount of free charges produced and delivered by a surface dielectric barrier discharge fluid‐ dynamics actuator. Different linear actuators and supplying conditions have been considered. Actuators were utilized to produce an ionic wind impinging an insulating target surface. Charged particles' distribution over the target was measured with and without a metallic mesh between the actuator and target itself. Linear actuators have proven to be more effective in charge delivery with respect to an annular one previously studied by our research team. A two‐ dimensional electrostatic finite‐element analysis has been carried out to get a better insight into this physical behavior.

In this paper, an investigation on an annular Plasma Synthetic Jet Actuator (PSJA) utilizing a Surface Dielectric Barrier Discharge (SDBD) is reported. The work is focused at an investigation of the electric charges transported by the jet produced by the actuator and deposited on a target. Particularly, an assessment of the various factors that may affect the charge deposit process has been carried out. Experiments have been performed in a controlled environment with different electric configurations. This allowed to evaluate how the humidity rate affects and the dynamics of the electric charge build-up process. It was observed that humidity rate weakly affects the charge deposition, being the most notable effect an increase of the deposition time for higher humidity rate. Moreover, the performances of two different power supply systems, working at different voltage and frequency conditions, were compared. The two supplies have been set up do feed the actuator with the same power, in order to assess which voltage-frequency condition is more efficient at depositing electric charge on the target. It was observed that a higher applied electric field produces higher charge deposition rates.

This paper reports the characterization of a low-power, atmospheric pressure plasma source developed for and successfully tested in applications of plasma medicine. The source produces plasma by ionizing a helium flow containing traces of air. The effluent gas is thus enriched in reactive oxygen and nitrogen species as well as helium metastable excited states. Electrical measurements, Schlieren imaging, OES and various chemical analyses and probes enabled us to fully characterize the plasma source and to determine some fundamental parameters for treating living samples such as the power feeding the discharge, the optimal source to target distance, the maximum exposure time, and to identify the major chemical species responsible for the biological action on exposed living matter.

Annular plasma synthetic jet actuators demonstrated their ability to produce a tubular flow normal to the surface where the dielectric barrier discharge (DBD) is ignited. These fluid-dynamic actuators enhance the delivery of reactive species towards the target to be treated. In these actuators, long life charged particles are generated within the plasma region and then carried on by the induced flow. In this work, the potential distribution induced by charges deposited over an insulating target has been measured. Surface DBD actuators, made with different dielectric materials, have been supplied by different sinusoidal voltages at a constant average power supplying the discharge. Actuators with the exposed electrode connected to both the high voltage potential and grounded have been tested. The charge distribution accumulated on a target surface perpendicular to the flow has been measured at different time intervals with the plasma on. Charges advected by the flow are always positive. The potential distribution on the target surface generated by the charges has been measured. For both configurations, firstly an M-shaped distribution develops and, later on, it becomes bell-shaped. A charge build-up mechanism has been found to be faster when the exposed electrode is connected to the high voltage terminal. The target has been placed at a variable distance from 1 to 5 cm from the actuator surface. At a distance of 5 cm, induced potentials are two times smaller than those with the target at 1 cm. Measurements allow us to estimate a charge flux toward the target on the order of 1011 particles (cm2 s)−1. The results presented in this work show that the presence of charged particles in the jet flow outside the plasma could be an important factor to be accounted for when these plasma actuators are used for treatment purposes (indirect plasma treatment).

In this work ozone concentration in a plane-to-plane Dielectric Barrier Discharge (DBD) reactor has been evaluated both experimentally and numerically. The reactor geometry has been chosen to generate a homogenous discharge. Therefore, simplified approaches for both experiments and numerical simulations have been utilized. The discharge was excited for 20 s in atmospheric-pressure quiescent air by means of a sinusoidal voltage of 15 kV peak at a frequency of 5 kHz in continuous operation. Electrical and optical measurements have been done to estimate the input parameters for the kinetics model. The ozone density within the discharge gap was measured by using the UV absorption method. The optical path travelled by the UV beam inside the reactor gap was estimated by means of Schlieren imaging. Within the time intervals and the dimensions considered, plasma was assumed to be uniform. This assumption was confirmed experimentally by iCCD images of the discharge. Numerical simulations have been performed by means of the zero-dimensional open-source code ZDPlasKin. A set of 622 reactions among 62 chemical species has been implemented, accounting for a 1% water vapour fraction. Reduced electric field, electron density and gas temperature were the input parameters of the code. Ozone density presented a production peak of about 1.3 ⋅ 1017 cm−3 half a second after discharge ignition. A steady state value of 6 ⋅ 1016 cm−3 was reached after a transient of about 12 s. Numerical simulation delivered ozone concentrations in good agreement with experimental data. Graphical abstract: [Figure not available: see fulltext.].

Plasma synthetic jet actuators (PSJAs) demonstrated their ability to produce a tubular flow normal to the surface where the dielectric barrier discharge (DBD) is ignited. These fluid dynamics actuators enhance the delivery of reactive and charged species toward the target to be treated. In this work, the efficacy of an octagonal PSJA used to indirectly treat Candida guilliermondii, both in agar substrate and in saline solution, was experimentally studied. The inactivation effect of free charges advected by the induced flow has been investigated as well by interposing a metallic mesh between the actuator surface and the treated sample. Therefore, the passage of charges and their migration toward the sample can either be allowed or prevented simply by having the mesh floating or connected to the ground, respectively. A 4 log and a 2 log colony-forming unit (CFU) reduction were observed for agar substrate and saline solution, respectively, at the highest energy dose treatment with the grid grounded. Under the same conditions but with the grid at floating potential, the presence of advected charges gives an additional 1 log CFU. In addition to biological tests, chemical analyses have been carried out to identify the most important modifications produced by the induced flow into treated water. Results presented in this work demonstrate the efficacy of PSJAs in indirect treatment of C. guilliermondii, both on agar substrate and saline solution, and the inactivation properties of free charges advected by this type of fluid dynamics actuator.

In this work several planar dielectric barrier discharge fluid-dynamics actuators have been experimentally investigated. The actuator is made by an electrode pair separated by a dielectric. It is characterized by a planar geometry and it induces a volume force on the gas above it which modifies the fluid-dynamics within the aerodynamic boundary layer. Several actuator geometries, dielectric materials, a.c. supply voltages and supply frequencies have been used. Rotational and vibrational temperatures have been determined by means of spectroscopic measurements. Vibrational temperatures have been found to be one order of magnitude higher than the rotational ones, confirm-ing the non-thermal behavior of the discharge. The translational temperature has been evaluated by thermographic observations of the dielectric surface heated by the plasma. The values of the translational temperature are in a very good agreement with those of the rotational temperature. Electric measurements have been carried out to determine the average power delivered to the discharge and to estimate the average electron number density. In the plasma induced by the discharge above the actuator an average electron density of 4 ÷ 15 · 1017 m-3 has been determined. The gas speed of the induced wall jet has been measured with a Pitot tube. The average power delivered to the electrodes increas-es with a power law of the applied voltage (exponent ≈ 3 ÷ 5) and linearly with the supply frequency. The induced speed increases with the increase of the average power until a plateau is reached. The efficiencies of the different actuators have been compared by evaluating the relation between average power and induced gas speed.

The electrohydrodynamic (EHD) interaction induced in atmospheric air pressure by a surface dielectric barrier discharge (DBD) actuator has been experimentally investigated. Plasma synthetic jet actuators (PSJAs) are DBD actuators able to induce an air stream perpendicular to the actuator surface. These devices can be used in the field of aerodynamics to prevent or induce flow separation, modify the laminar to turbulent transition inside the boundary layer, and stabilize or mix air flows. They can also be used to enhance indirect plasma treatment effects, increasing the reactive species delivery rate onto surfaces and liquids. This can play a major role in plasma processing and chemical kinetics modelling, where often only diffusive mechanisms are considered. This paper reports on the importance that different electrode geometries can have on the performance of different PSJAs. A series of DBD aerodynamic actuators designed to produce perpendicular jets has been fabricated on two-layer printed circuit boards (PCBs). Both linear and annular geometries were considered, testing different upper electrode distances in the linear case and different diameters in the annular one. An AC voltage supplied at a peak of 11.5 kV and a frequency of 5 kHz was used. Lower electrodes were connected to the ground and buried in epoxy resin to avoid undesired plasma generation on the lower actuator surface. Voltage and current measurements were carried out to evaluate the active power delivered to the discharges. Schlieren imaging allowed the induced jets to be visualized and gave an estimate of their evolution and geometry. Pitot tube measurements were performed to obtain the velocity profiles of the PSJAs and to estimate the mechanical power delivered to the fluid. The optimal values of the inter-electrode distance and diameter were found in order to maximize jet velocity, mechanical power or efficiency. Annular geometries were found to achieve the best performance.

A high-voltage high-frequency single-phase arbitrary waveform voltage generator able to supply a wide range of plasma reactors is proposed in this paper. The generator structure is based on the cascaded H-bridge multilevel topology, including 24 H-bridge basic modules with the capability of 49 output voltage levels. The individual H-bridge dc supply (600V) is provided by a flyback converter fed by a low-voltage (12V) dc battery. In this way, the input isolation of the ±14.4kV maximum output voltage is realized in a simple and effective manner, and a portable device is obtained. The multilevel generator has been tested by supplying a dielectric barrier discharge (DBD) fluid-dynamic plasma actuator with different voltage waveforms, pointing out a wide and interesting set of results in terms of output plasma currents, and a first comparison has been carried out with respect to a conventional AC sinusoidal generator. A simplified circuit model has been introduced for the DBD plasma actuator, and the whole system has been numerically implemented by Simulink of Matlab. The simulation results are in good agreement with the experiments.

The research on nanofluids has shown important improvements of the electrical performance, but so far the attention has only been focused on their use in transformers. The target of this work is to understand if nanofluids can be applied as insulators for power electronics modules, where the major stresses are caused by square waves or PWM voltages. Breakdown events in non-uniform field conditions and different voltage configurations have been deeply investigated revealing the effects of space charge mechanisms. While for DC fields the nanofluids contribution is positive, a completely different conclusion can be evinced from sinusoidal and square waves, where the situation even worsens at higher frequencies. Schlieren images of breakdown events seem to confirm the postulated hypotheses.

Surface dielectric barrier discharges (S-DBDs) have received renewed attention in recent years for their potential application in emerging biomedical, environmental and agricultural applications. In most of these applications, the plasma is not in direct contact with the substrate being treated and the transport of reactive species from the plasma to the substrate is typically assumed to be controlled by diffusion. Here, we demonstrate that generally this is not the case and that electrohydrodynamic (EHD) forces can produce jets that enhance the delivery of these species, thereby influencing the efficacy of the S-DBD device. In particular, we have studied the degradation of potassium indigotrisulfonate solutions exposed to S-DBDs generated in devices with annular electrodes of diameters varying between 10 mm and 50 mm. All the devices were driven at constant linear power density (watts per cm of plasma length) and although local plasma properties remained the same in all the devices, a three-fold efficacy enhancement was observed for devices of diameter ∼30 mm due to EHD effects.

Active flow control has recently received an increasing attention since it allows to directly manipulate the flow-field around a surface only when it is effectively requested. Aerodynamic plasma actuators supplied by a dielectric barrier discharge (DBD) can be used for this purpose. Usually, sinusoidal voltages in the range 5–50 kV peak and frequencies between 1 and 100 kHz are utilized to ignite this plasma typology. The surface discharge produced by these devices is able to tangentially accelerate the flow field by means of the electrohydrodynamic (EHD) interaction. DBDs generate non-thermal plasmas characterized by low input energies and limited temperature increments. Plasma actuators can be easily designed by following the shape of the aerodynamic body and can be used over heat-sensitive surfaces. These aerodynamic devices have demonstrated to produce boundary layer modifications with induced speeds up to 10 m/s. Their use over airfoils, flaps, and blades have shown the possibility to delay the transition between laminar to turbulent regime, to prevent flow separation enhancing lift and reducing drag. Moreover, the adoption of these actuators over landing gears and trailing edges may induce a noise reduction effect. Dielectric materials, electrodes configuration, and supplying waveforms are most relevant parameters to be considered to enhance actuator performance. On a parallel plane, on/off actuation strategy is a key point in the use of these devices when utilized over aerodynamic surfaces impinged within an external flow.

A new bench-top reactor employing a streamer discharge in air was developed and tested for potential use in an advanced oxidation stage in water treatment processes. The complex heterogeneous system and the ensuing chemical processes were characterized using an integrated approach to map the morphology of the plasma/gas/liquid interface, identify the plasma short-lived excited species, determine the oxidants in solution and monitor the organic pollutants degradation. Three model pollutants were used in these experiments, rhodamine B, phenol and metolachlor. The first two are common standards used to evaluate the performance of advanced oxidation processes. Metolachlor is a widely used herbicide listed among the most important recalcitrant emerging organic pollutants. Energy efficiency, kinetics and products of our tests show a good performance of the reactor. Specifically, mineralization appears feasible also in the case of metolachlor.

The magnetohydrodynamics interaction around a conical test body in a hypersonic argon flow is experimentally investigated. The hypersonic flow is realized in the high-enthalpy arc-heated wind tunnel of Alta Societa per Azioni (S.p.A.) (Pisa, Italy) at Mach 6. The aim of experimental activity is to produce an experimental data base to be used for the validation of numerical codes for the analysis of the magnetohydrodynamics interaction. The magnetohydrodynamics interaction is obtained in the shock layer of the conical test body at the exit of the hypersonic nozzle. The electrical configuration realized allows one to enhance the effect of the magnetohydrodynamics interaction on the plasma parameters. This is done using the Hall field to generate the magnetohydrodynamics interaction and by short-circuiting the Faraday current inside the plasma of the shock layer. The magnetic flux density is produced by an array of three magnets located in the test body. Tests are performed at three different stagnation pressures. Fluid-dynamic, electrical, and optical observations have been done. The experiment showed a considerable effect of the magnetohydrodynamics interaction on the values of the quantities measured.

— The MHD interaction around a conical test body in a hypersonic argon flow was experimentally investigated. The aim of the experiment was to produce a data base to be used for the validation of numerical codes for the analysis and the simulation of the magneto-fluid dynamics in hypersonic flows. In these ex-periments the flow was obtained in the high-enthalpy arc-heated hypersonic wind tunnel – HEAT - of Alta (Pisa-Italy). Speeds at Mach 6 were reached. In the present experiment the flow and the plasma characteristics have been determined. The MHD interac-tion was obtained in the shock layer of a conical test body placed at the exit of the hypersonic nozzle. The realized electrical con-figuration allowed to enhance the effect of the MHD interaction on the plasma parameters. This was done by utilizing the Hall field to generate the MHD interaction and by short-circuiting the Faraday current inside the plasma of the shock layer. The mag-netic flux density was produced by an array of three magnets located in the test body. Test runs were performed at three differ-ent stagnation pressures. Fluid-dynamic, electrical and optical observations have been done. The experiment showed a large effect of the MHD interaction on the values of the measured quan-tities. In order to have a test body entirely contained in the region where a uniform hypersonic flow has been measured, a test body of smaller sizes has been constructed and tested. The results ob-tained in this case confirm the results of the tests with the larger body.

none 13 si In this contribution, a poly(butylene succinate)-based copolymer containing thioether linkages (P(BS85BTDG15)) has been synthesized and characterized from the molecular, thermal and mechanical point of view. The results have been compared to the parent homopolymer. Films obtained both by PBS and P(BS85BTDG15) have been subjected to surface modification by means of non-thermal plasma surface treatment and the effect on physic/mechanical properties has been considered. Hydrolytic degradation rate under physiological conditions and in vitro biocompatibility of treated and non-treated polymeric films have been also investigated. The introduction of thioether linkages and the plasma etching enhanced the polymer surface wettability, thus resulting in an increased hydrolytic degradation rate. On the other hand, bulk properties were not significantly affected. Biocompatibility assays highlighted the absence of potentially cytotoxic products into the culture medium and proved that the investigated polymeric films can support cell adhesion and proliferation. mixed Fabbri, Martina; Gigli, Matteo; Costa, Michela; Govoni, Marco; Seri, Paolo; Lotti, Nadia; Giordano, Emanuele; Munari, Andrea; Gamberini, Rita; Rimini, Bianca; Neretti, Gabriele; Cristofolini, Andrea; Borghi, Carlo A Fabbri, Martina; Gigli, Matteo; Costa, Michela; Govoni, Marco; Seri, Paolo; Lotti, Nadia; Giordano, Emanuele; Munari, Andrea; Gamberini, Rita; Rimini, Bianca; Neretti, Gabriele; Cristofolini, Andrea; Borghi, Carlo A

A surface dielectric barrier discharge (DBD) actuator has been experimentally investigated. An electrode pair separated by a dielectric sheet constitutes the actuator. Two types of dielectric materials and several a.c. supply conditions have been utilized to generate a surface dielectric barrier discharge with different characteristics. An Electro Hydro Dynamics (EHD) interaction was induced into still air and several fluid-dynamic regimes were obtained. Using electric and fluid dynamics measurements, the energy transfer mechanisms caused by the EHD interaction have been investigated. The visualization of the plasma boundary layer during the discharge ignition phase, characterized by hot vortexes, and during the steady regime has been obtained by means of Schlieren diagnostics technique. Vortex morphology and propagation velocities for both actuator types at all supply conditions have been evaluated. Pitot velocity profiles have been taken in the steady regime operation at several distances along a line perpendicular to the actuator surface. Along this line and as a function of the position the integral of the pixel intensities of the Schlieren image has been calculated. The function obtained matches with a good agreement the Pitot velocity profile for all distances and in all the supply conditions investigated. Numerical simulations were performed to validate theoretically this result. The calculations confirm the relationship between flow velocity distribution in the boundary layer and the gas density distribution.

In this work several plane dielectric barrier discharge actuators had been experimentally investigated. Each actuator is constituted by a planar electrode pair separated by a dielectric. Several actuator geometries, dielectric materials, and a.c. supply voltages and frequencies have been utilized. Rotational and vibrational temperatures have been appraised through spectroscopic measurements. Translational temperatures have been evaluated by thermographic investigations, and the fluid speed has been obtained by using a Pitot tube. Electric measurements have been performed to determine the average power and the electron number density. All these parameters have been correlated to evaluate the best configuration and operating conditions for the considered actuators.

A high-voltage high-frequency arbitrary waveform voltage generator able to supply a wide range of plasma reactors is proposed in this paper. The generator structure is based on the cascaded H-bridge multilevel topology, including 24 H-bridge basic modules with the capability of 49 output voltage levels. The individual H-bridge dc supply (600V) is provided by a flyback converter fed by a low-voltage (12V) dc battery. In this way, the input isolation of the ±15kV maximum output voltage is realized in a simple and effective manner, and a portable device is obtained. The generator has been tested by supplying a DBD plasma actuator with different voltage waveforms, up to 20 kHz, pointing out a wide and interesting set of results in terms of output plasma currents.

This work reports an experimental investigation performed in wind tunnel facility on a NACA0015 airfoil equipped with a set of vectorizable fluid-dynamic DBD plasma actuators. The ability of the actuators to recover the stall condition with free stream velocities in the range 5-23 m/s has been investigated. The discharge has been generated by feeding the actuators with a sinusoidal voltage waveform with a frequency of 15 kHz and voltages up to 7.5 kV peak. The actuator positioned on the leading edge exhibits highest ability in the stall recovery. Unsteady actuation obtained by alternatively switching on and off the discharge is more effective in the stall recovery when compared with a steady actuation. The frequency that optimizes the stall recovery has been found to be a function of the velocity with the power of 1.5. This result leads to the determination of a constant Strouhal number if the boundary layer thickness is used as characteristic length. Finally the lift coefficient, obtained when the plasma actuator has been turned on, has been found to be a linear function of the applied voltage.

In this work a low-temperature plasma source for the generation of plasma activated water (PAW) is developed and characterized. The plasma reactor was operated by means of an atmospheric-pressure air dielectric barrier discharge (DBD). The plasma generated is in contact with the water surface and is able to chemically activate the liquid medium. Electrodes were supplied by both sinusoidal and nanosecond-pulsed voltage waveforms. Treatment times were varied from 2 to 12 min to increase the energy dose released to the water by the DBD plasma. The physics of the discharge was studied by means of electrical, spectroscopic and imaging diagnostics. The interaction between the plasma and the liquid was investigated as well. Temperature and composition of the treated water were detected. Images of the discharges showed a filamentary behaviour in the sinusoidal case and a more homogeneous behaviour in the nanosecond-pulsed one. The images and the electrical measurements allowed to evaluate an average electron number density of about 4 × 1019 and 6 × 1017 m-3 for the sinusoidal and nanosecond-pulsed discharges respectively. Electron temperatures in the range of 2.1÷2.6 eV were measured by using spectroscopic diagnostics. Rotational temperatures in the range of 318-475 K were estimated by fitting synthetic spectra with the measured ones. Water temperature and pH level did not change significantly after the exposure to the DBD plasma. The production of ozone and hydrogen peroxide within the water was enhanced by increasing the plasma treatment time and the energy dose. Numerical simulations of the nanosecond-pulsed discharge were performed by using a self-consistent coupling of state-to-state kinetics of the air mixture with the Boltzmann equation of free electron kinetics. Temporal evolution of the electron energy distribution function shows departure from the Maxwellian distribution especially during the afterglow phase of the discharge. When limited deviations from Maxwellian distribution were observed, calculated electron temperature is in good agreement with the one measured by means of spectroscopic diagnostics. Computed temporal evolution of the energy delivered to the discharge is comparable with the one obtained from electrical measurements. The electrical discharges supplied by both voltage waveforms produce plasma activated water with negligible thermal effects and pH variations.

Summary form only given. The paper considers the charge deposited on the surface of a plasma dielectric barrier discharge (DBD) actuator. The actuator is utilized to induce the electro-hydro-dynamic (EHD) interaction in the aerodynamic boundary layer of one atmosphere air [1,2]. The effect on the EHD interaction of the charge distribution on the actuator surface is studied both experimentally and numerically.

This paper deals with the measurements performed to characterize the jet produced by the plasma wind tunnel SCIROCCO. The measurements are aimed to determine the vibrational temperature and the electron density of the plasma flow. A numerical rebuilding of the expansion trough the nozzle has then been performed. The work is part of an experimental activity funded by the European Space Agency and by the Italian Space Agency in the framework of a conjunct research project on the MHD interaction in an unseeded hypersonic air flow.

The operation of a surface dielectric barrier discharge actuator for airflow control has been experimentally investigated. The actuator is constituted by an electrode pair separated by a dielectric Teflon sheet. Several ac supply conditions have been utilized. An electrohydrodynamics interaction was induced in still air, and several fluid-dynamic regimes were obtained. Visualization of the plasma boundary layer during the discharge ignition phase and during the steady state regime was obtained by utilizing a Schlieren diagnostic technique. The vortex morphology and propagation velocities at all supply conditions utilized have been evaluated. Velocity profiles perpendicular to the actuator surface, obtained from Pitot tube measurements, and line intensity profiles, determined by means of Schlieren imaging, have been determined for the steady regime operation. The integral along a line perpendicular to the actuator surface of the light intensity of the Schlieren image has been calculated. The profile obtained is in good agreement with the Pitot velocity profile in all the supply conditions investigated. Numerical simulations were also performed. The calculations confirm the relation between the flow velocity distribution in the boundary layer and the gas density distribution, which is the cause of the Schlieren image.

This summary paper is related to the experimental investigation on the magneto fluid dynamic interaction around a blunt test body immersed into a hypersonic unseeded air flow. The experiments have been carried out in the CIRA owned plasma wind tunnel SCIROCCO. Two test conditions have been utilized for the experiments, with a total pressure of 2.5 and 2.3 bar respectively and a total specific enthalpy of 16 and 12.1 MJ/kg, and the air flow accelerated in the nozzle up to Mach 10. The magnetic induction field is generated by an electromagnet enclosed in the test article, and can reach a 0.8 T maximum value in the interaction region. The numerical rebuilding of the experimental data was carried out on a restricted set of experimental conditions. Two different CIRA codes have been used, CAST and EMC3NS. The two codes, whose structure is generally similar, are different is some modeling aspects. Their results compared with experimental data have been analyzed and critically compared. The work has been conjunctly funded by the European Space Agency and The Italian Space Agency. © 2012 the authors.

The Electro-Hydro-Dynamics (EHD) interaction, induced by a dielectric barrier discharge (DBD) in the aerodynamic boundary layer induced in a one atmosphere still air, has been studied both numerically and experimentally. Three different geometrical actuator configurations have been used. The first one is constituted by an electrode pair separated by a 2 mm dielectric teflon sheet. The second and the third configuration have been obtained by adding a third electrode on the upper dielectric surface. This electrode has been placed downstream of the upper electrode and has been connected to the ground or has been left floating. The high voltage electrode has been fed by an a.c. electrical signal. Measurements of the dielectric surface potential generated by the charge deposition have been obtained by using an electrostatic voltmeter. Numerical simulations allowed to determine the charge distribution on the dielectric surface. The discharge has been switched off after positive and negative values of the plasma current. The measurements have been carried out after both phases. Surface potential distributions show that the charge build up takes place several centimeters downstream the upper electrode after the end of the plasma extension. The charge distribution strongly depends on the switching off phase and is heavily affected by the geometrical configuration. Velocity profiles are obtained by using a Pitot probe. They show that the third electrode limits the fluid dynamics performance of the actuator. A relation between the charge surface distribution and the EHD interaction phenomenon has been found. Images of the plasma have been taken to evaluate the discharge structure and the extension of the plasma in the different geometrical configurations studied.

A surface dielectric barrier discharge (DBD) actuator has been experimentally investigated. An electrode pair separated by a dielectric sheet constitutes the actuator. Two types of dielectric materials and several a.c. supply conditions have been utilized to generate a surface dielectric barrier discharge with different characteristics. An Electro Hydro Dynamics (EHD) interaction was induced into still air and several fluid-dynamic regimes were obtained. Using electric and fluid dynamics measurements, the energy transfer mechanisms caused by the EHD interaction have been investigated. The visualization of the plasma boundary layer during the discharge ignition phase, characterized by hot vortexes, and during the steady regime has been obtained by means of Schlieren diagnostics technique. Vortex morphology and propagation velocities for both actuator types at all supply conditions have been evaluated. Pitot velocity profiles have been taken in the steady regime operation at several distances along a line perpendicular to the actuator surface. Along this line and as a function of the position the integral of the pixel intensities of the Schlieren image has been calculated. The function obtained matches with a good agreement the Pitot velocity profile for all distances and in all the supply conditions investigated. Numerical simulations were performed to validate theoretically this result. The calculations confirm the relationship between flow velocity distribution in the boundary layer and the gas density distribution.

An advanced flow control experiment, concerning magnetohydrodynamics (MHD) interaction over a blunt body, has been designed by Alta, CIRA and Department of Electrical Engineering (DIE) of University of Bologna and to be realized in CIRA's plasma wind tunnel "Scirocco" under a technology research program (TRP) funded by the European Space Agency (ESA). This work is a further step of the researches performed during the last decade by Alta and DIE in the field of MHD interaction. This experimental campaign foresees the employment of a 50 kW electromagnet, enclosed into an insulated blunt-shaped metallic TPS convectively cooled and electrically insulated by a ceramic coating. The test article has been designed for an air flow with nominal stagnation conditions of p0=2 bar and h0=22 MJ/kg, but several other conditions are planned to be investigated. The aim of the experimental campaign, along with a better understanding of the physical phenomena occurring within an highly ionized shock layer with an applied magnetic field, is the comparison of the collected data with the numerical predictions of CFD codes developed by CIRA. © 2011 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

This paper deals with the design of an experiment devoted to MHD flow control, to be performed in CIRA GHIBLI hypersonic facility. The criteria utilized to define the proper test conditions and to design and realize the model are here described. The expansion in the nozzle has been investigated through numerical simulations in order to have a preliminary estimate of the ionization degree and of the heat fluxes over the test article. Moreover, an MFD code has been used in order to calculate the expected interaction effect, under the assumption of low Rem. The same procedure has been utilized for the design of an MHD test to be performed in the CIRA SCIROCCO facility .

This paper gives an overview of the experimental work on the MHD-hypersonic flow interaction, carried out in the High Enthalpy Arc Heated hypersonic wind Tunnel of Alta, Pisa, Italy, in cooperation with the Department of Electrical Engineering of the University of Bologna, under the support of The European Space Agency and the Italian Space Agency. The aim of the experiment was to produce a database to be used for the validation of numerical codes for the analysis and the simulation of the agnetofluid-dynamic interaction in hypersonic flows. In order to do this a grat attention has been dedicated to the diagnostics and mainly to those which can deliver experimental data to be compared with numerical results. In the experiments reported sharp and blunt bodies have been investigated at Mach 6 and Mach 15. The experiments have shown large effect of the MHD interaction at each of the experimental conditions investigated.

This paper describes the results of an experimental investigation on the effect of the MHD interaction in the plasma of the shock layer above a test body immersed into a hypersonic Argon flow. The hypersonic flow was obtained by means of the high-enthalpy arc-heated wind tunnel of Alta SpA at Mach 6 and Mach 15. An extensive activity was carried out in order to quantitatively characterize the weakly ionized free stream, for pressures in the range between 0.5 and 1.5 bar. Two different models, with embedded high strength magnets have been utilised: a sharp cone and a truncated-cone blunt body. The models are equipped with surface pressure measurement devices and electrostatic probes. Two geometrically identical, non magnetic models were used to compare results with and without MHD interaction. This paper will describe the experimental setup, the characterization activity, and the test campaign results. A short critical analysis on the obtained results will be also present including comparison with the past experiments conducted in Alta by the same team.

DBD plasma actuators driven by repetitive nanosecond pulses added to low frequency bias voltage are studied, and parametric results of plasma-induced thrust versus voltage profile parameters are presented. The results of the thrust measurements agree with schlieren visualization results obtained earlier and indicate that dielectric surface charge plays a major role in the thrust. Direct measurements of the dielectric surface potential and its dynamics show that charge builds up at the dielectric surface and extends far downstream of the plasma. For a sinusoidal voltage waveform, the dielectric surface charges positively. With the voltage waveform consisting of nanosecond pulses superimposed on a dc bias, the sign of the dielectric surface charge is the same as the sign (polarity) of the bias voltage. Based on the surface charge measurements, a modified configuration of DBD plasma actuator is proposed. Preliminary experiments show its effectiveness at relatively low voltages. Variations of the permittivity of dielectric with temperature and frequency were also considered in relation to their role in DBD actuator performance.