1,721,012 research outputs found
Effect of the charge surface distribution on the flow field induced by a dielectric barrier discharge actuator
No full textThe Electro-Hydro-Dynamics (EHD) interaction induced by a surface dielectric barrier discharge
in the aerodynamic boundary layer at one atmosphere still air has been investigated. Three
different geometrical configurations of the actuator have been utilized. In the first configuration, an
electrode pair separated by a 2mm dielectric sheet has been used. The second and the third
configurations have been obtained by adding a third electrode on the upper side of the dielectric
surface. This electrode has been placed downstream of the upper electrode and has been connected
to ground or has been left floating. Three different dielectric materials have been utilized. The high
voltage upper electrode was fed by an a.c. electric tension. Measurements of the dielectric surface
potential generated by the charge deposition have been done. The discharge has been switched off
after positive and negative phases of the plasma current (the current phase was characterized by a
positive or a negative value, respectively). The measurements have been carried out after both
phases. The charge distribution strongly depended on the switching off phase and was heavily
affected by the geometrical configuration. A remarkable decrease of the charge deposited on the
dielectric surface has been detected when the third electrode was connected to ground. Velocity
profiles were obtained by using a Pitot probe. They showed that the presence of 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. Imaging of the plasma has been
done to evaluate the discharge structure and the extension of the plasma in the configurations
investigated
Experimental and Numerical Investigation on the Electro Hydro Dynamic Interaction generated by a Dielectric Barrier Discharge
No full textA 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
Plasma Parameters and Electromagnetic Forces Induced by the MHD Interaction in an Hypersonic Argon Flow Experiment
No full textThis work proposes an experimental analysis on the magneto hydro dynamic (MHD) interaction induced by a magnetic test body immersed into a hypersonic argon flow. The characteristic plasma
parameters are measured. They are related to the voltages arising in the Hall direction and to the variation of the fluid dynamic properties induced by the interaction. The tests have been performed in a hypersonic wind tunnel at Mach 6 and Mach 15. The plasma parameters are measured in the stagnation region in front of the nozzle of the wind tunnel and in the free stream region at the nozzle exit. The test body has a conical shape with the cone axis in the gas flow direction and the cone vertex against the flow. It is placed at the nozzle exit and is equipped with three permanent magnets. In the configuration adopted, the Faraday current flows in a closed loop completely immersed into
the plasma of the shock layer. The electric field and the pressure variation due to MHD interaction have been measured on the test body walls. Microwave adsorption measurements have been used for the determination of the electron number density and the electron collision frequency. Continuum recombination radiation and line radiation emissions have been detected. The electron temperature has been determined by means of the spectroscopic data by using different methods. The electron number density has been also determined by means of the Stark broadening of H(alfa) and the H(beta) lines. Optical imaging has been utilized to visualize the pattern of the electric current distribution in the
shock layer around the test body. The experiments show a considerable effect of the electromagnetic forces produced by the MHD interaction acting on the plasma flow around the test body. A
comparison of the experimental data with simulation results shows a good agreement
Charge distribution on the surface of a dielectric barrier discharge actuator for the fluid-dynamic control
No full textThe electric potential distribution induced on the surface of an aerodynamic plasma actuator, operating by means of a surface dielectric barrier discharge (DBD), has been studied both numerically and experimentally. Three actuators made with three different dielectric materials (Teflon, Plexiglas, and glass) have been used. The geometric configuration of the three actuators is the same one. An electrode pair separated by a 2mm thick dielectric sheet constitutes the DBD actuator. The exposed high voltage electrode has been fed by a 5 kHz a.c. electrical signal. Voltage values between 7.5 and 15 kVp have been used. Measurements of the distribution of the electrical potential in the dielectric surface, generated by the charge deposited on it, have been done. Numerical simulations allowed to evaluating the charge distribution on the dielectric surface. The discharge has been switched off after positive and negative plasma currents. The measurements have been carried out after both phases. The potential distribution is always positive. The charge build up takes place several centimeters downstream of the upper electrode for an extension broader than that of the plasma on the dielectric surface. The charge distribution strongly depends on the switching off phase and is heavily affected by the dielectric material. In order to evaluate the discharge structure and the extension of the plasma, images have been taken also
Experimental and Numerical Investigation on a DBD Actuator for Airflow Control, Paper AIAA 2011-3912
No full textA surface dielectric barrier discharge (DBD) actuator has been experimentally investi-gated. 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
Experimental Activities on the MHD Interaction in a Hypersonic Air Flow Around a Blunt Body
No full textThis 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
Influence of the On-time on the Ozone Production in Pulsed Dielectric Barrier Discharges
Full text linkUnderstanding 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
Experimental Investigations on a Hypersonic Nitrogen Flow for Magneto Fluid Dynamic Interaction around a Blunt Body
No full textThis paper is focused on the plasma diagnostics utilized for the characterization of a hypersonic nitrogen flow. The nitrogen flow has been utilized for a test campaign on Magneto Fluid Dynamics interaction in the frame of the ASI (Italian Space Agency) funded project CAST (Advanced Aerothermodynamic Configurations for Space Transport). Microwave absorption measurements have been performed in plasma free jet conditions in order to determine the electron number density of the plasma flow. Further investigations have been performed utilizing a LIF measurement technique
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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