Active flow control is a topic in full expansion due to associated industrial applications of huge importance, particularly for aeronautics. Among all flow control methods, such as the use of mechanical flaps, wall synthetic jets or MEMS, plasma-based devices are very promising. The main advantages of such systems are their robustness, simplicity, low power consumption and ability for real-time control at high frequency. This paper is a review of the worldwide works on this topic, from its origin to the present. It is divided into two main parts. The first one is dedicated to the recent knowledge concerning the electric wind induced by surface non-thermal plasma actuators, acting in air at atmospheric pressure. Typically, it can reach 8 m s−1 at a distance of 0.5 mm from the wall. In the second part, works concerning active airflow control by these plasma actuators are presented. Very efficient results have been obtained for low-velocity subsonic airflows (typically U∞ ≤ 30 m s−1 and Reynolds number of a few 105), and promising results at higher velocities indicate that plasma actuators could be used in aeronautics.

https://iopscience.iop.org/article/10.1088/0022-3727/40/3/S01/pdf

Airflow control by non-thermal plasma actuators

Flow Separation Control by Plasma Actuator with Nanosecond Pulsed-Periodic Discharge

Carbon nanotubes produced in arcs have been found to have the form of multiwalled fullerenes, at least over short lengths. Sintering of the tubes to each other is the predominant source of defects that limit the utility of these otherwise perfect fullerene structures. The use of a water-cooled copper cathode minimized such defects, permitting nanotubes longer than 40 micrometers to be attached to macroscopic electrodes and extracted from the bulk deposit. A detailed mechanism that features the high electric field at (and field-emission from) open nanotube tips exposed to the arc plasma, and consequent positive feedback effects from the neutral gas and plasma, is proposed for tube growth in such arcs.

https://science.sciencemag.org/content/sci/266/5188/1218.full.pdf

Growth and sintering of fullerene nanotubes.

Experimental and theoretical studies were undertaken to investigate the particulatefree secondary flow interaction in the wire-type electrostatic precipitator. The secondary flow generated by the corona discharge is not negligible, and strong flow interactions take place owing to the induced circulatory cells. The calculated numerical results demonstrate close agreement with experiment.

Electrohydrodynamics in an electrostatic precipitator

The electrohydrodynamic (EHD) enhancement mechanism is first outlined in this paper. A comprehensive review of past work on EHD single and two-phase heat transfer, as well as past work in the related area of EHD-induced flow, is then presented. Correlation attempts are also reviewed. Recent experimental results for EHD boiling and condensation in single- and multi-tube heat exchangers are discussed. A description of the possible practical EHD electrode systems for applications in power production cycles and regrigeration is also presented. The research work needed to clarify outstanding questions in EHD and encourage its use in practical systems is discussed.

Electrohydrodynamic enhancement of heat transfer and fluid flow

The corona wind, with a velocity of several meters per second, is caused by applying high electric tension to bring about corona discharge in gases. In this paper the corona wind is experimentally and theoretically analyzed from an electrohydrod ynamical (EHD) standpoint. Experiments have been performed mainly in nitrogen by a two-dimensional electrode arrangement of a fine wire anode and a plate cathode. The voltage-current characteristics of an electrostatic probe indicate that positive ions predominate in the whole space except in an extremely narrow region close to the wire. A theoretical analysis has been conducted based on the model that positive ions produced by ionization near the wire electrode move toward the plate, introducing the bulk convective motion of neutral molecules as the result of collisions of ions and neutral molecules. The electric potential distribution in the space and pressure distribution on the plate calculated numerically agree well with the experimental data. Consequently, it is made clear that the corona wind is caused by the Coulomb force exerted on ions and collisions of ions and neutral molecules of gas.

Akira Yabe

Papers

EHD study of the corona wind between wire and plate electrodes

Heat transfer augmentation around a downward-facing flat plate by non-uniform electric fields