Actuators are transducers that convert an electrical signal to a desired physical quantity. Active flow control actuators modify a flow by providing an electronically controllable disturbance. The field of active flow control has witnessed explosive growth in the variety of actuators, which is a testament to both the importance and challenges associated with actuator design. This review provides a framework for the discussion of actuator specifications, characteristics, selection, design, and classification for aeronautical applications. Actuator fundamentals are discussed, and various popular actuator types used in low-to-moderate speed flows are then described, including fluidic, moving object/surface, and plasma actuators. We attempt to highlight the strengths and inevitable drawbacks of each and highlight potential future research directions.

Actuators for Active Flow Control

Plasma-assisted ignition and combustion

Journal of Physics D: Applied Physics published the first Plasma Roadmap in 2012 consisting of the individual perspectives of 16 leading experts in the various sub-fields of low temperature plasma science and technology. The 2017 Plasma Roadmap is the first update of a planned series of periodic updates of the Plasma Roadmap. The continuously growing interdisciplinary nature of the low temperature plasma field and its equally broad range of applications are making it increasingly difficult to identify major challenges that encompass all of the many sub-fields and applications. This intellectual diversity is ultimately a strength of the field. The current state of the art for the 19 sub-fields addressed in this roadmap demonstrates the enviable track record of the low temperature plasma field in the development of plasmas as an enabling technology for a vast range of technologies that underpin our modern society. At the same time, the many important scientific and technological challenges shared in this roadmap show that the path forward is not only scientifically rich but has the potential to make wide and far reaching contributions to many societal challenges.

/pdf/the-2017-plasma-roadmap-low-temperature-plasma-science-and-1x1mdft0yo.pdf

The 2017 Plasma Roadmap: Low temperature plasma science and technology

Dielectric Barrier Discharges (DBDs) are plasmas generated in configurations with an insulating (dielectric) material between the electrodes which is responsible for a self-pulsing operation. DBDs are a typical example of nonthermal atmospheric or normal pressure gas discharges. Initially used for the generation of ozone, they have opened up many other fields of application. Therefore DBDs are a relevant tool in current plasma technology as well as an object for fundamental studies. Another motivation for further research is the fact, that so-called partial discharges in insulated high voltage systems are special types of DBDs. The breakdown processes, the formation of structures, and the role of surface processes are currently under investigation. This review is intended to give an update to the already existing literature on DBDs considering the research and development within the last two decades. The main principles and different modes of discharge generation are summarized. A collection of known as well as special electrode configurations and reactor designs will be presented. This shall demonstrate the different and broad possibilities, but also the similarities and common aspects of devices for different fields of applications explored within the last years. The main part is devoted to the progress on the investigation of different aspects of breakdown and plasma formation with the focus on single filaments or microdischarges. This includes a summary of the current knowledge on the electrical characterization of filamentary DBDs. In particular, the recent new insights on the elementary volume and surface memory mechanisms in these discharges will be discussed. An outlook for the forthcoming challenges on research and development will be given. Page 1 of 47 AUTHOR SUBMITTED MANUSCRIPT PSST-101368.R1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A cc ep e M nu sc rip t Progress on DBD Sources and Filaments 2

/pdf/dielectric-barrier-discharges-progress-on-plasma-sources-and-47w32a77wl.pdf

Dielectric barrier discharges: progress on plasma sources and on the understanding of regimes and single filaments

: The efficacy of dielectric barrier discharge (DBD) plasmas driven by high voltage (approximately 15 kV) repetitive nanosecond pulses approximately 100 ns FWHM) for flow separation control is investigated experimentally on an airfoil leading edge up to Re=1x106 (62 m/s). Unlike AC-DBDs, the nanosecond pulse driven DBD plasma actuator transfers very little momentum to the neutral air, but generates compression waves similar to localized arc filament plasma actuators. A complex pattern of quasi-planar and spherical compression waves is observed in still air. Measurements suggest that some of these compression waves are generated by discharge filaments that remain fairly reproducible pulse-to-pulse. The device performs as an active trip at high Re pre-stall angles of attack and provides perturbations that generate coherent spanwise vortices at post-stall. These coherent structures entrain freestream momentum thereby reattaching the normally separated flow to the suction surface of the airfoil. Coherent structures are identified at all tested frequencies, but values of F(subponent c, exponent +)=4-6 are most effective for control. Such devices which are believed to function through thermal effects could be an alternative to AC-DBD plasmas that rely on momentum addition.

Separation control with nanosecond-pulse-driven dielectric barrier discharge plasma actuators

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

This paper presents a detailed explanation of the physical mechanism of the nanosecond pulsed surface dielectric barrier discharge (SDBD) effect on the flow. Actuator-induced gas velocities show near-zero values for nanosecond pulses. The measurements performed show overheating in the discharge region on fast (? 1??s) thermalization of the plasma input energy. The mean values of such heating of the plasma layer can reach 70?K, 200?K and even 400?K for 7?ns, 12?ns and 50?ns pulse durations, respectively. The emerging shock wave together with the secondary vortex flows disturbs the main flow. The resulting pulsed-periodic disturbance causes an efficient transversal momentum transfer into the boundary layer and further flow attachment to the airfoil surface. Thus, for periodic pulsed nanosecond dielectric barrier discharge, the main mechanism of impact is the energy transfer and heating of the near-surface gas layer. The following pulse-periodic vortex movement stimulates redistribution of the main flow momentum.

https://iopscience.iop.org/article/10.1088/0963-0252/18/3/034015/pdf

SDBD plasma actuator with nanosecond pulse-periodic discharge

Currently, the problem of flow active control by low-temperature plasma is considered to be one of the most booming realms of aerodynamics . The paper presents a results on controlling boundary layer attachment by plasma actuator withhighvoltage pulsed periodic nanosecond excitation. Actuator-induced gas velocities show near-zero values for nanosecond pulses. The measurements performed show overheating in the discharge region at fast (T ? 1?s) thermalization of the plasma inputed energy. The mean values of such heating of the plasma layer can reach 70, 200, and even 400 K for 7-, 12-, and 50-ns pulse durations, respectively. The emerging shock wave together with the secondary vortex flows disturbs the main flow. The resulting pulsed-periodic disturbance causes an efficient transversal momentum transfer into the boundary layer and further flow attachment to the airfoil surface. Thus, for periodic pulsed nanosecond dielectric barrier discharge DBD, the main mechanism of impact is the energy transfer to and heating of the near-surface gas layer. The following pulse-periodic vortex movement stimulates redistribution of the main flow momentum. The experiments performed here have shown high efficiency of the given mechanism to control boundary layer separation, lift and drag force coefficients, and acoustic noise reduction in the Mach number range of 0.05 to 0.85. The design of the SDBD was typical asymmetric plasma actuator with one exposed and one covered electrodes . In our experiments, the exposed electrode was a cathode. The lower covered electrode was an anode. The experiments were carried out on the generator with a pulse length of 12 ns. Two regimes of the generator's operation were used. One was periodic, with a constant frequency of pulses fed onto the discharge gap. The other was burst mode, with impulses fed in bursts. The number of pulses in a burst varied from 1 to 100 with a repetition frequency of 100 kHz, and the time between the bursts being 1-100 ms. The number of pulses in the burst varied to produce constant averaged discharge power for various experimental conditions. The mean power in all burst regimes was equal to 25 W.The electrodes were made of 50 ?m aluminum foil. Their length was 90 cm and their widths were 15 and 10 mm for the lower and upper electrodes, respectively. The dielectric layer consisted of three PVC-films with a total thickness of 240 ?m.

Andrei Nikipelov

Papers

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

SDBD plasma actuator with nanosecond pulse-periodic discharge

Flow separation control by plasma actuator with nanosecond pulse periodic discharge

Acoustic Noise and Flow Separation Control by Plasma Actuator

Boundary Layer Separation Control by Nanosecond Plasma Actuator