1,408 research outputs found
Active flow control by using plasma actuators
No full textActive 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
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 investigation on the energy transfer in a DBD plasma actuator for airflow control
No full textDetermination of the velocity profile in a DBD plasma flow by means of Schlieren imaging
No full textIn this work a dielectric barrier discharge fluid dynamic actuator has been experimentally investigated. A planar electrode pair separated by a dielectric constitutes the actuator. Four a.c. supply voltages at a fixed frequency have been utilized in order to generate different fluid dynamic regimes in still air. The visualization of the hot wall jet generated by the Electro Hydro Dynamic interaction has been achieved by using Schlieren diagnostics technique. Pitot velocity profiles have been obtained at several distances from the upper electrode. Along the same lines the integral of the pixel intensities of the Schlieren image has been calculated. The obtained function matches, with good agreement, with the Pitot velocity profile for all the distances in all the supply conditions
Experimental Activities on the MHD Interaction in a Hypersonic Argon and Nitrogen Flows
No full textThis paper reports the experimental activities on MHD flow control carried out in Italy in the framework of few research projects. Experiments has been carried out in argon and nitrogen hypersonic flows. In the experiments reported, sharp and blunt bodies has been investigated at Mach 6 and Mach 15. Some detail of the experiments performed in CIRA Ghibli hypersonic facility are given. In Ghibli, the MHD interaction around a blunt body in a nitrogen flow has been investigated. The criteria utilized to define the proper test conditions and to design and realize the model are here described. 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
Experimental determination and numerical evaluation under simplifying assumptions of the ozone concentration in an atmospheric-pressure air DBD plasma
No full textAbstract: 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 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 the charge distribution in a DBD plasma actuator surface for airflow control
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