A 3-D DNS and experimental study of the effect of the recirculating flow pattern inside a reactive kernel produced by nanosecond plasma discharges in a methane-air mixture

Castela, Maria; Stepanyan, Sergey; Fiorina, Benoît; Coussement, Axel; Gicquel, Olivier; Darabiha, Nasser; Laux, Christophe O.

doi:10.1016/j.proci.2016.06.174

Cited by 62 publications

(43 citation statements)

References 30 publications

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“…Similar to Castela et al [13], and in agreement with the measurements performed by Rusterholtz et al [27], we assumed 20 % of the measured energy going into ultrafast heating for all inter-electrode gap cases simulated here. This assumption was supported by the best match of the dynamics observed experimentally (moment of shockwave detachment and propagation, kernel size).…”

Section: Numerical Setupsupporting

confidence: 79%

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: Numerical Setupsupporting

confidence: 79%

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

Dumitrache¹,

Gallant²,

Minesi³

et al. 2019

J. Phys. D: Appl. Phys.

Self Cite

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“…In this scenario, a perfectly symmetric torus will be obtained (with no third lobe observed) since the vortex pair will have equal strength. Such kernel dynamics are sometimes encountered in nanosecond pin-to-pin discharges when the energy is distributed homogenously inside the electrode gap [24,38,39]. Moreover, while the present focus is on NIR laser sparks, the mechanism described here can also be used to explain the hydrodynamics observed in visible and ultra-violet laser induced plasma.…”

Section: Mechanism Of Vorticity Generationmentioning

confidence: 90%

Gas dynamics and vorticity generation in laser-induced breakdown of air

Dumitrache¹,

Yalin²

2020

Opt. Express

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Research has shown that the ignition characteristics of laser induced plasmas in fuel-air mixtures are influenced by the gas dynamics effects induced during the gas breakdown stage. Here, we present numerical modeling of the fluid mechanics induced by breakdown (plasma formation) from a nanosecond near-infrared (NIR) laser pulse in air. The simulations focus on the post-discharge kernel dynamics with the goal of developing a better understanding on how vorticity is generated during the kernel cooling phase. Initial conditions (ICs) of kernel shape, temperature and pressure (corresponding to the end of the laser pulse) are found from experimental Rayleigh scattering data. It is shown that this method for determining ICs is preferred versus use of the Taylor-Sedov blast wave theory as it provides a more accurate description of the starting field. Past experimental observations have revealed that the gas dynamics of nanosecond laser sparks typically lead to the formation of an asymmetric torus with a frontal lobe propagating towards the laser source. We show that the development of the asymmetric torus is governed by strong vorticity generated through baroclinic torque arising from the blast wave that forms at the kernel boundary. Initially, the blast takes the shape of the teardrop kernel but then evolves into a spherical front during the first ~10 µs because the blast wave strength varies along its circumference. This spatial variation leads to a misalignment between the pressure and density gradients and generation of vorticity by baroclinic torque. Ultimately, the observed flow-field is dictated by how the energy was initially deposited around the beam waist during breakdown. As such, one can tailor the aerodynamics induced during the cooling and recombination phase by controlling the energy deposition profile.

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“…Similar mechanisms to those discussed here (in the context of laser ignition) are also responsible for kernel dynamics induced by conventional spark plugs and in nanosecond discharges between electrode pairs. However, in these cases the energy deposition is more symmetric so that two matched vortex rings persist and no third lobe forms 29 – 32 . Finally, Endo et al .…”

Section: Introductionmentioning

confidence: 99%

Control of Early Flame Kernel Growth by Multi-Wavelength Laser Pulses for Enhanced Ignition

Dumitrache

VanOsdol

Limbach

et al. 2017

Sci Rep

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The present contribution examines the impact of plasma dynamics and plasma-driven fluid dynamics on the flame growth of laser ignited mixtures and shows that a new dual-pulse scheme can be used to control the kernel formation process in ways that extend the lean ignition limit. We perform a comparative study between (conventional) single-pulse laser ignition (λ = 1064 nm) and a novel dual-pulse method based on combining an ultraviolet (UV) pre-ionization pulse (λ = 266 nm) with an overlapped near-infrared (NIR) energy addition pulse (λ = 1064 nm). We employ OH* chemiluminescence to visualize the evolution of the early flame kernel. For single-pulse laser ignition at lean conditions, the flame kernel separates through third lobe detachment, corresponding to high strain rates that extinguish the flame. In this work, we investigate the capabilities of the dual-pulse to control the plasma-driven fluid dynamics by adjusting the axial offset of the two focal points. In particular, we find there exists a beam waist offset whereby the resulting vorticity suppresses formation of the third lobe, consequently reducing flame stretch. With this approach, we demonstrate that the dual-pulse method enables reduced flame speeds (at early times), an extended lean limit, increased combustion efficiency, and decreased laser energy requirements.

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A 3-D DNS and experimental study of the effect of the recirculating flow pattern inside a reactive kernel produced by nanosecond plasma discharges in a methane-air mixture

Cited by 62 publications

References 30 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

Gas dynamics and vorticity generation in laser-induced breakdown of air

Control of Early Flame Kernel Growth by Multi-Wavelength Laser Pulses for Enhanced Ignition

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