Hydrodynamic ejection caused by laser-induced optical breakdown

Wang, Jonathan M.; Buchta, David; Freund, Jonathan B.

doi:10.1017/jfm.2019.1066

Cited by 21 publications

(12 citation statements)

References 61 publications

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“…This detailed understanding of the role of the vortex rings in the mixing and cooling process of the hot gas kernel has wide-ranging implications for momentum transport and passive scalar mixing in plasma-based flow and combustion control techniques. The model can help guide further research on a variety of plasma discharges where the presence of vortex rings has been established [31]- [33].…”

Section: Discussionmentioning

confidence: 99%

Two regime cooling in flow induced by a spark discharge

et al. 2020

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The cooling process associated with the flow induced by a spark plasma discharge generated between a pair of electrodes is measured using stereoscopic particle image velocimetry (S-PIV) and background oriented schlieren (BOS). Density measurements show that the hot gas kernel initially cools fast by convective cooling, followed by a slower cooling process. The cooling rates during the fast regime range from being 2 to 10 times those in the slower regime. An analytical model is developed to relate the cooling observed in the fast regime from BOS, to the total entrainment of cold ambient fluid per unit volume of the hot gas kernel, measured from S-PIV. The model calculates the cooling ratio to characterize the cooling process and shows that the cooling ratio estimated from the density measurements are in close agreement with those calculated from the entrainment. These measurements represent the first ever quantitative density and velocity measurements of the flow induced by a spark discharge and reveal the role of entrainment on the cooling of the hot gas kernel. These results underscore that convective cooling of the hot gas kernel, in the fast regime, leads to approximately 50% of the cooling and occurs within the first millisecond of the induced flow.

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Section: Discussionmentioning

confidence: 99%

Two regime cooling in flow induced by a spark discharge

et al. 2020

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“…This model differs critically from (18) in the prescription of f (x): asymmetry in the geometry of the energy kernel can lead to laser-generated flow that transports hot gas over distances much larger than the initial kernel and impacts the ignition outcome [29,6,33]. Additional details on the laser model, the simulation setup, and ignition dynamics can be found elsewhere [44,46,45].…”

Section: Physical Modelmentioning

confidence: 99%

An integrated heterogeneous computing framework for ensemble simulations of laser-induced ignition

Maeda¹,

Teixeira²,

Wang³

et al. 2022

Preprint

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An integrated computational framework is introduced to study complex engineering systems through physicsbased ensemble simulations on heterogeneous supercomputers. The framework is primarily designed for the quantitative assessment of laser-induced ignition in rocket engines. We develop and combine an implicit programming system, a compressible reacting flow solver, and a data generation/management strategy on a robust and portable platform. We systematically present this framework using test problems on a hybrid CPU/GPU machine. Efficiency, scalability, and accuracy of the solver are comprehensively assessed with canonical unit problems. Ensemble data management and autoencoding are demonstrated using a canonical diffusion flame case. Sensitivity analysis of the ignition of a turbulent, gaseous fuel jet is performed using a simplified, three-dimensional model combustor. Our approach unifies computer science, physics and engineering, and data science to realize a cross-disciplinary workflow. The framework is exascale-oriented and can be considered a benchmark for future computational science studies of real-world systems.

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“…After the shock wave departure, the flow field is comprised of a hot gas kernel and vortex ring(s). The number of vortex rings, their dynamics, and the hot gas kernel evolution depend on the spark generation method [7][8][9][10][11][12][13]. In laser sparks, for instance, a pair of vortex rings of unequal strength and size are induced [8,14], while in sparks generated between conetipped electrodes (pin-to-pin discharges), a pair of two almost identical vortex rings are induced [9][10][11] and in surface discharges, a single vortex ring is formed that propagates away from the discharge surface [12].…”

Section: Introductionmentioning

confidence: 99%

“…In these cases, the strength and dynamics of the vortex ring(s) control the spatial extent and cooling of the hot gas kernel and thus play a critical role in engineering applications. In laser sparks, which are typically used for combustion applications, the vortex ring characteristics control the direction and ejection of the hot gas kernel [8], affecting ignition and flame growth [14]. In pin-to-pin electrical spark discharges, the rings entrain cold ambient gas into the hot kernel to promote rapid cooling/mixing, and this determines the required pulsation frequency of the discharges to utilize the synergetic effect of multiple pulses to optimize ignition systems [15] or to stabilize flames and promote efficient combustion [16][17][18].…”

Section: Introductionmentioning

confidence: 99%

“…Despite the critical role vortex rings play in the flow induced by spark discharges, to the best of our knowledge, there has been no quantitative experimental investigation on the source of this vorticity. Researchers have used computational fluid dynamics (CFD) simulations to study the flow field at early times during the spark induced shock wave, and have suggested that there are two possible sources of vorticity generation, both through a baroclinic effect: (a) vorticity production due to the non-uniformity in the shock strength [3,19,20] and (b) vorticity production due to the interaction of pressure gradients behind the shock wave with the hot gas kernel [7,8,19,[21][22][23]. In laser sparks, the second mechanism has been shown to be the dominant source of vorticity generation because the blast wave expands out of the field of view, depositing vorticity rapidly, while the pressure gradients and expansion waves following the blast wave interact with the low density region from the hot gas kernel for longer periods of time and generate more vorticity than the shock wave.…”

Section: Introductionmentioning

confidence: 99%

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Shock generated vorticity in spark discharges

Singh

Rajendran

Vlachos

et al. 2021

J. Phys. D: Appl. Phys.

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Spark discharges induce a complex flow field consisting of a shock wave at early times (∼1 µs), a pair of vortex rings, and a hot gas kernel. The vortex rings entrain ambient gas into the hot gas kernel and control its cooling and expansion. In this work, we investigate the shock wave's contribution in producing the vortex ring vorticity. We analyze high-speed (700 kHz) schlieren images of the shock wave for a range of electrical energies to measure the shock properties and estimate shock velocity and curvature. These measurements are combined with a model to calculate the vorticity generated. The measurements show that the highest vorticity is generated near the peak shock curvature location, and the shock curvature and strength increase with electrical energy deposited. A comparison of the vorticity estimated from the model to vorticity measurements from stereoscopic particle image velocimetry shows the results to be statistically equivalent. This suggests that the shock curvature and velocity contribute to the vortex rings induced by spark discharges.

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Hydrodynamic ejection caused by laser-induced optical breakdown

Cited by 21 publications

References 61 publications

Two regime cooling in flow induced by a spark discharge

Two regime cooling in flow induced by a spark discharge

An integrated heterogeneous computing framework for ensemble simulations of laser-induced ignition

Shock generated vorticity in spark discharges

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