Jet regime of the afterspark channel decay

Leonov, Sergey B.; Isaenkov, Yuri I.; Firsov, A. A.; Nothnagel, S. L.; Gimelshein, S. F.; Shneider, Mikhail N.

doi:10.1063/1.3429675

Cited by 25 publications

(11 citation statements)

References 20 publications

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“…In reality, the discharge kernel is not perfectly axisymmetric for large gaps. Moreover, the existence of Rayleigh-Taylor instabilities into the gas at later times break the kernel symmetry [37]. Nonetheless, the main dynamics are captured in both scenarios and the code predicts well the transition from a torus to a diffusive kernel as the inter-electrode gap is increased.…”

Section: B Numerical Modelingmentioning

confidence: 83%

Hydrodynamic regimes induced by nanosecond pulsed discharges in air: mechanism of vorticity generation

Dumitrache¹,

Gallant²,

Minesi³

et al. 2019

J. Phys. D: Appl. Phys.

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The mechanisms controlling the hydrodynamic effects induced by nanosecond pulsed discharges applied between two pin electrodes in air at atmospheric conditions are investigated experimentally and numerically. A cylindrical plasma kernel is formed between the electrodes during the discharge. After the discharge, schlieren images show that the cylindrical kernel evolves in different ways depending on the gap distance: (1) for short gap distances (), the cylindrical kernel collapses to form a torus-like structure. In this case, the flow field presents a significant source of vorticity; (2) for larger gaps (), the kernel retains its initial cylindrical shape and cools down primarily through heat diffusion. The objective of this work is to understand the mechanisms leading to the formation of these two hydrodynamic regimes. To this end, simulations were performed and compared with the experimental schlieren images. It is shown that the main source of vorticity is the baroclinic torque caused by the cylindrical blast wave that follows the fast energy addition during the discharge. Finally, a criterion is given to predict the occurrence of the two hydrodynamic regimes. This criterion is then validated against experimental results from the literature.

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Section: B Numerical Modelingmentioning

confidence: 83%

Hydrodynamic regimes induced by nanosecond pulsed discharges in air: mechanism of vorticity generation

Dumitrache¹,

Gallant²,

Minesi³

et al. 2019

J. Phys. D: Appl. Phys.

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“…The processes mentioned above are well illustrated in refs. [139,143]. Note that no jets are observed at short inter-electrode gaps d < 10 mm and when the peak power is lower than 10 MW.…”

Section: Turbulent Decay Of Pulsed Discharge Channelmentioning

confidence: 95%

“…The physical mechanism of development of this instability was considered in [139,143]: the fast cooling of the axial zone leads to the decrease of the gas pressure that leads to the reverse motion of the gas. Such a motion is unstable due to the Rayleigh-Taylor mechanism [138,143]. An estimate of the instability development time t ≈ 100 µs agrees well with the value observed experimentally.…”

Section: Turbulent Decay Of Pulsed Discharge Channelmentioning

confidence: 99%

Electrically Driven Supersonic Combustion

Leonov

2018

Energies

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This manuscript reviews published works related to plasma assistance in supersonic combustion; focusing on mixing enhancement, ignition and flameholding. A special attention is paid for studies, which the author participated in person. The Introduction discusses general trends in plasma-assisted combustion and, specifically, work involving supersonic conditions. In Section 2, the emphasis is placed on different approaches to plasma application for fuel ignition and flame stabilization. Several schemes of plasma-based actuators for supersonic combustion have been tested for flameholding purposes at flow conditions where self-ignition of the fuel/air mixture is not realizable due to low air temperatures. Comparing schemes indicates an obvious benefit of plasma generation in-situ, in the mixing layer of air and fuel. In Section 3, the problem of mixing enhancement using a plasma-based technique is considered. The mechanisms of interaction are discussed from the viewpoint of triggering gasdynamic instabilities promoting the kinematic stretching of the fuel-air interface. Section 4 is related to the description of transitional processes and combustion instabilities observed in plasma-assisted high-speed combustion. The dynamics of ignition and flame extinction are explored. It is shown that the characteristic time for reignition can be as short as 10 ms. Two types of flame instability were described which are related to the evolution of a separation zone and thermoacoustic oscillations, with characteristic times 10 ms and 1 ms correspondingly.

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“…The physical mechanism of this instability was considered in [38,41]: cooling of the axial zone leads to the pressure decrease with sequential gas reverse movement. Such a movement is unstable owing to the Rayleigh-Taylor mechanism [34,41]. The estimation of the instability development time t ≈ 100 µs appears in a good agreement with the experimentally observed value.…”

Section: Mixing Enhancement Experimentsmentioning

confidence: 99%

“…The analysis of experimental data taken in ambient air and in high-speed flow returns a not obvious result concerning the size of disturbed zone: its value is several times bigger than it should be in accordance with laminar or turbulent diffusion mechanisms [40][41][42]. This happens because of generation of intensive lateral jets on the last stage of expansion followed by fast turbulization of the gas in significant volume, comparable to the gap distance, as is shown in figure 9c.…”

Section: Mixing Enhancement Experimentsmentioning

confidence: 99%

Plasma-enhanced mixing and flameholding in supersonic flow

Firsov

Savelkin

Yarantsev

et al. 2015

Phil. Trans. R. Soc. A.

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The results of experimental study of plasma-based mixing, ignition and flameholding in a supersonic model combustor are presented in the paper. The model combustor has a length of 600 mm and cross section of 72 mm width and 60 mm height. The fuel is directly injected into supersonic airflow (Mach number M = 2, static pressure P st = 160-250 Torr) through wall orifices. Two series of tests are focused on flameholding and mixing correspondingly. In the first series, the near-surface quasi-DC electrical discharge is generated by flush-mounted electrodes at electrical power deposition of W pl = 3-24 kW. The scope includes parametric study of ignition and flame front dynamics, and comparison of three schemes of plasma generation: the first and the second layouts examine the location of plasma generators upstream and downstream from the fuel injectors. The third pattern follows a novel approach of combined mixing/ignition technique, where the electrical discharge distributes along the fuel jet. The last pattern demonstrates a significant advantage in terms of flameholding limit. In the second series of tests, a long discharge of submicrosecond duration is generated across the flow and along the fuel jet. A gasdynamic instability of thermal cavity developed after a deposition of high-power density in a thin plasma filament promotes the air-fuel mixing. The technique studied in this work has weighty potential for high-speed combustion applications, including cold start/restart of scramjet engines and support of transition regime in dual-mode scramjet and at offdesign operation.

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Jet regime of the afterspark channel decay

Cited by 25 publications

References 20 publications

Hydrodynamic regimes induced by nanosecond pulsed discharges in air: mechanism of vorticity generation

Hydrodynamic regimes induced by nanosecond pulsed discharges in air: mechanism of vorticity generation

Electrically Driven Supersonic Combustion

Plasma-enhanced mixing and flameholding in supersonic flow

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