Implementation of large scale shadowgraphy in hydrogen explosion phenomena

Dennis, Kadeem; Maley, Logan; Liang, Zhe; Radulescu, Matei I.

doi:10.1016/j.ijhydene.2014.05.002

Cited by 11 publications

(5 citation statements)

References 5 publications

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“…1. A large-scale Edgerton shadowgraph technique [17] was implemented using a 2-m by 2-m retro-reflective screen using a high speed camera and a Xenon arc continuous light source [18]. A row of cylindrical obstacles of 16-mm-diameter were placed at the entrance of the visual section of the shock tube to allow for visualization of the fast flames established downstream.…”

Section: Methodsmentioning

confidence: 99%

Chapman–Jouguet deflagrations and their transition to detonation

Saif

Wang

Pękalski

et al. 2017

Proceedings of the Combustion Institute

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We study experimentally fast flames and their transition to detonation in mixtures of methane, ethane, ethylene, acetylene, and propane mixtures with oxygen. Following the interaction of a detonation wave with a column of cylinders of varying blockage ratio, the experiments demonstrate that the fast flames established are Chapman-Jouguet deflagrations, in excellent agreement with the self-similar model of Radulescu et al. [1]. The experiments indicate that these Chapman-Jouguet deflagrations dynamically restructure and amplify into fewer stronger modes until the eventual transition to detonation. The transition length to a self-sustained detonation was found to correlate very well with the mixtures' sensitivity to temperature fluctuations, reflected by the χ parameter introduced by Radulescu, which is the product of the non-dimensional activation energy E a /RT and the ratio of chemical induction to reaction time t i /t r . Correlation of the measured DDT lengths determined that the relevant characteristic time scale from chemical kinetics controlling DDT is the energy release or excitation time t r . Correlations with the cell size also capture the dependence of the DDT length on χ for fixed blockage ratios.

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Section: Methodsmentioning

confidence: 99%

Chapman–Jouguet deflagrations and their transition to detonation

Saif

Wang

Pękalski

et al. 2017

Proceedings of the Combustion Institute

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“…Explosions, gunshots, and harsh environments are natural subjects for study by the Edgerton retroreflective shadowgraph technique [73,[130][131][132][133][134][135]. It has also found application inside the test sections of large high-speed wind tunnels [46,136,137].…”

Section: Retroreflective Shadowgraphymentioning

confidence: 99%

A review of recent developments in schlieren and shadowgraph techniques

Settles¹,

Hargather

2017

Meas. Sci. Technol.

328

154

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Schlieren and shadowgraph techniques are used around the world for imaging and measuring phenomena in transparent media. These optical methods originated long ago in parallel with telescopes and microscopes, and although it might seem that little new could be expected of them on the timescale of 15 years, in fact several important things have happened that are reviewed here. The digital revolution has had a transformative effect, replacing clumsy photographic film methods with excellent-though expensive-high-speed video cameras, making digital correlation and processing of shadow and schlieren images routine, and providing an entirely-new synthetic schlieren technique that has attracted a lot of attention: background-oriented schlieren or BOS. Several aspects of modern schlieren and shadowgraphy depend upon laptop-scale computer processing of images using an imagecapable language such as MATLAB ™. BOS, shock-wave tracking, schlieren velocimetry, synthetic streak-schlieren, and straightforward quantitative density measurements in 2D flows are all recent developments empowered by this digital and computational capability.

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“…The visualization of the detonation wave front evolution in the diverging channels was performed using a large-scale shadowgraph system described by Dennis et al (2014). A high speed Phantom V1210 camera was used for visualization.…”

Section: Methodsmentioning

confidence: 99%

Dynamics of detonations with a constant mean flow divergence

Radulescu

Borzou

2018

J. Fluid Mech.

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An exponential horn geometry is introduced in order to establish cellular detonations with a constant mean lateral mass divergence, propagating at quasi-steady speeds below the Chapman-Jouguet value. The experiments were conducted in 2C 2 H 2 +5O 2 +21Ar and C 3 H 8 +5O 2 . Numerical simulations were also performed for weakly unstable cellular detonations to test the validity of the exponential horn geometry. The experiments and simulations demonstrated that such quasi-steady state detonations can be realized, hence permitting to obtain the relations between the detonation speed and mean lateral flow divergence for cellular detonations in an unambiguous manner. The experimentally obtained speed (D) dependencies on divergence (K) were compared with the predictions for steady detonations with lateral flow divergence obtained with the real thermochemical data of the mixtures. For the 2C 2 H 2 +5O 2 +21Ar system, reasonable agreement was found between the experiments and steady wave prediction, particularly for the critical divergence leading to failure. Observations of the reaction zone structure in these detonations indicated that all the gas reacted very close to the front, as the transverse waves were reactive. The experiments obtained in the much more unstable detonations in C 3 H 8 +5O 2 showed significant differences between the experimentally derived D(K) curve and the prediction of steady wave propagation. The latter was found to significantly under-predict the detonability of cellular detonations. The transverse waves in this mixture were found to be non-reactive, hence permitting to shed off non-reacted pockets, which burn via turbulent flames on their surface. It is believed that the large differences between experiment and the inviscid model in this class of cellular structures is due to the importance of diffusive processes in the burn-out of the non-reacted pockets. The empirical tuning of a global one step chemical model to describe the macro-scale kinetics in cellular detonations revealed that the effective activation energy was lower by 14% in 2C 2 H 2 +5O 2 +21Ar and 54% in the more unstable C 3 H 8 +5O 2 system. This confirms previous observations that diffusive processes in highly unstable detonations are responsible for reducing the thermal ignition character of the gases processed by the detonation front. † Email address for correspondence: matei@uottawa.ca arXiv:1606.05323v2 [physics.flu-dyn]

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Implementation of large scale shadowgraphy in hydrogen explosion phenomena

Cited by 11 publications

References 5 publications

Chapman–Jouguet deflagrations and their transition to detonation

Chapman–Jouguet deflagrations and their transition to detonation

A review of recent developments in schlieren and shadowgraph techniques

Dynamics of detonations with a constant mean flow divergence

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