Andrea Cristofolini

Charge distribution on the surface of a dielectric barrier discharge actuator for the fluid-dynamic control

The 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 2u2009mm thick dielectric sheet constitutes the DBD actuator. The exposed high voltage electrode has been fed by a 5u2009kHz a.c. electrical signal. Voltage values between 7.5 and 15u2009kVp 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 distr...

Experimental investigation on a vectorized aerodynamic dielectric barrier discharge plasma actuator array

The Electro-Hydro-Dynamics (EHD) interaction, induced in atmospheric pressure still air by a surface dielectric barrier discharge (DBD) actuator, had been experimentally studied. A plasma aerodynamic actuator array, able to produce a vectorized jet, with the induced airflow oriented toward the desired direction, had been developed. The array was constituted by a sequence of single surface DBD actuators with kapton as dielectric material. An ac voltage in the range of 0–6u2009kV peak at 15u2009kHz had been used. The vectorization had been obtained by feeding the upper electrodes with different voltages and by varying the electrical connections. The lower electrodes had been connected either to ground or to the high voltage source, to produce the desired jet orientation and to avoid plasma formation acting in an undesired direction. Voltage and current measurements had been carried out to evaluate waveforms and to estimate the active power delivered to the discharge. Schlieren imaging allowed to visualize the induc...

A plasma aerodynamic actuator supplied by a multilevel generator operating with different voltage waveforms

In this work a high voltage—high frequency generator for the power supply of a dielectric barrier discharge (DBD) plasma actuator for the aerodynamic control obtained by the electro-hydro-dynamic (EHD) interaction is described and tested. The generator can produce different voltage waveforms. The operating frequency is independent of the load characteristics and does not require impedance matching. The peak-to-peak voltage is 30 kV at a frequency up to 20 kHz and time variation rates up to 60 kV μs−1. The performance of the actuator when supplied by several voltage waveforms is investigated. The tests have been performed in still air at atmospheric pressure. Voltage and current time behaviors have been measured. The evaluation of the energy delivered to the actuator allowed the estimation of the periods in which the plasma was ignited. Vibrational and rotational temperatures of the plasma have been estimated through spectroscopic acquisitions. The flow field induced in the region above the surface of the DBD actuator has been studied and the EHD conversion efficiency has been evaluated for the voltage waveforms investigated. The nearly sinusoidal multilevel voltage of the proposed generator and the sinusoidal voltage waveform of a conventional ac generator obtain comparable plasma features, EHD effects, and efficiencies. Inverse saw tooth waveform presents the highest effects and efficiency. The rectangular waveform generates suitable EHD effects but with the lowest efficiency. The voltage waveforms that induce plasmas with higher rotational temperatures are less efficient for the conversion of the electric into kinetic energy.

Wind Tunnel Experiments on a NACA0015 Airfoil Equipped with Vectorizable Dielectric Barrier Discharge Plasma Actuators

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.

Charge distribution on the surface of a dielectric barrier discharge actuator

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.

Development of a Multilevel Plasma Generator for Dielectric Barrier Discharge Actuators

In this work the development and the testing of a high voltage high frequency plasma generator to supply Dielectric Barrier Discharge (DBD) actuators for the aerodynamic control, is reported. The generator can produce a wide set of different voltage waveforms. The peak-to-peak electrical tension is 30 kV at a frequency up to 20 kHz. The operating frequency are independent of the load characteristics and are not subject to requirements on impedance matching. The generator has been tested when supplying a DBD actuator for aerodynamic control based on the Electro-Hydro-Dynamic (EHD) interaction. The tests have been performed in still air. The flow induced in the region above the surface of the actuator has been investigated and the EHD efficiency has been evaluated. The sinusoidal voltage waveform, simulated by the multilevel generator, and the sinusoidal voltage waveform of a conventional generator obtain comparable EHD effects and efficiencies. The sinusoidal and the inverse saw-tooth voltage waveforms show the best efficiencies with regard to the EHD interaction.

Assessment of AC interference caused by transmission lines on buried metallic pipelines using F.E.M.

The focus of this paper is on the implementation and subsequent improvement of a technique for computing AC interference on buried metallic pipelines due to nearby power transmission lines. In order to perform this task, the finite element method (F.E.M.) is employed. After performing a description of the implementation of the classic F.E.M. approach, a hybrid technique designed to reduce the size of the mesh and therefore the computational time is presented. The results obtained with the two approaches are finally compared.

A COMPARISON BETWEEN CARSON'S FORMULAE AND A 2D FEM APPROACH FOR THE EVALUATION OF AC INTERFERENCE CAUSED BY OVERHEAD POWER LINES ON BURIED METALLIC PIPELINES

In this paper, the AC interference produced by an overhead power transmission line on a buried metallic pipeline is estimated using a circuital method based on the well-known Carson’s formulae and a two-dimensional finite element numerical code. The finite element formulation used in this paper implicitly takes into account the mutual inductive coupling between all the considered conductors, and it allows a more detailed analysis in cases where a nonhomogeneous soil is present. The FEM approach includes a procedure which has been developed to enforce that the sum of the currents flowing through the soil, pipeline and eventual overhead ground wire is equal to zero. A case study has been identified, and the results obtained by the two approaches have been compared and discussed.