Numerical Simulation of the Deflagration-to-Detonation Transition in Inhomogeneous Mixtures

Ettner, F.; Vollmer, Klaus G.; Sattelmayer, Thomas

doi:10.1155/2014/686347

Cited by 91 publications

(36 citation statements)

References 51 publications

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“…It is worth clarifying that the mesh size of 1 mm in the straight tube was sufficiently small to predict the energy release through the detonation process, as reported by Ettner 22 and validated through the comparison with the prior experiments as reported in the following section.…”

Section: Numerical Domainmentioning

confidence: 81%

Multi-stage nozzle-shape optimization for pulsed hydrogen–air detonation combustor

Ornano

Braun

Saracoglu

et al. 2017

Advances in Mechanical Engineering

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Thermal engines based on pressure gain combustion offer new opportunities to generate thrust with enhanced efficiency and relatively simple machinery. The sudden expansion of detonation products from a single-opening tube yields thrust, although this is suboptimal. In this article, we present the complete design optimization strategy for nozzles exposed to detonation pulses, combining unsteady Reynolds-averaged Navier-Stokes solvers with the accurate modeling of the combustion process. The parameterized shape of the nozzle is optimized using a differential evolution algorithm to maximize the force at the nozzle exhaust. The design of experiments begins with a first optimization considering steady-flow conditions, subsequently followed by a refined optimization for transient supersonic flow pulse. Finally, the optimized nozzle performance is assessed in three dimensions with unsteady Reynolds-averaged Navier-Stokes capturing the deflagration-to-detonation transition of a stoichiometric, premixed hydrogen-air mixture. The optimized nozzle can deliver 80% more thrust than a standard detonation tube and about 2% more than the optimized results assuming steady-flow operation. This study proposes a new multi-fidelity approach to optimize the design of nozzles exposed to transient operation, instead of the traditional methods proposed for steady-flow operation.

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Section: Numerical Domainmentioning

confidence: 81%

Multi-stage nozzle-shape optimization for pulsed hydrogen–air detonation combustor

Ornano

Braun

Saracoglu

et al. 2017

Advances in Mechanical Engineering

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“…The hydrogen concentration distribution for the inhomogeneous mixture is shown in Figure 2. It should be noted that, as described by Ettner et al [8], the latter would have an identical homogenous hydrogen mole fraction with the former if it is kept for more than 60s before ignition to allow for hydrogen and air to mix uniformly. Six probe locations for pressure history are set at distances of 0. m, the monotonic increase of flame speed can be observed in experiment.…”

Section: Case Setupmentioning

confidence: 95%

“…Numerical simulations were conducted for the experimental set up of Ettner et al [8] for flame acceleration and DDT in hydrogen-air mixture with concentration gradients in an obstucted channel, which is 5.4 m long and 0.06 m high. Seven obstacles with the blockage ratio 60% (BR=2h/H) were mounted on the top and bottom walls.…”

Section: Case Setupmentioning

confidence: 99%

“…In other words, concentration gradients can result in significantly stronger flame acceleration compared to the homogeneous mixtures. Ettner et al [7,8] …”

Section: Introductionmentioning

confidence: 99%

“…In other words, concentration gradients can result in significantly stronger flame acceleration compared to the homogeneous mixtures. Ettner et al [7,8] developed a density-based code to simulate flame acceleration and DDT process within OpenFOAM® toolbox.…”

Section: Introductionmentioning

confidence: 99%

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Numerical simulation of flame acceleration and deflagration-to-detonation transition in hydrogen-air mixtures with concentration gradients

Wang

Wen

2017

International Journal of Hydrogen Energy

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The present study aims to test the capability of our newly developed density-based solver, ExplosionFoam, for flame acceleration (FA) and deflagration-to-detonation transition (DDT) in mixtures with concentration gradients which is of important safety concern. The solver is based on the open source computational fluid dynamics (CFD) platform OpenFOAM® and uses the hydrogen-air single-step chemistry and the corresponding transport coefficients developed by the authors. Numerical simulations have been conducted for the experimental set up of Ettner et al. [7], which involves flame acceleration and DDT in both homogeneous hydrogen-air mixture as well as an inhomogeneous mixture with concentration gradients in an obstucted channel. The predictions demonstrate good quantitative agreement with the experimental measurements in flame tip position, speed and pressure profiles. Qualitatively, the numerical simulations have reproduced well the flame acceleration and DDT phenomena observed in the experiment. The results have revealed that in the computed cases, DDT is induced by the interaction of the precursor inert shock wave with the wall close to high hydrogen concentration rather than with the obstacle. Some vortex pairs appear ahead of the flame due to the interaction between the obstacles and the gas flow caused by combustion-induced expansion, but they soon disappear after the flame passes through them. Hydrogen cannot be completely consumed especially in the fuel rich region. This is of additional safety concern as the unburned hydrogen can be potentially re-ignited once more fresh air is available in an accidental scenario, resulting in subsequent explosions.Keywords: hydrogen safety; flame acceleration; deflagration-to-detonation transition; inhomogeneous hydrogen-air mixture. INTRODUCTIONThe energy landscape is gradually shifting from fossil fuels to alternative renewable energy resources such as solar, wind, hydroelectric, etc. This change is also driven by the need to reduce pollutions from the combustion of fossil fuels, greenhouse effect and acid rain, etc. Hydrogen is seen as a promising clean energy carrier. This in turn requires the associated safety issues to be addressed.The accidental release of hydrogen into confined or semi-confined enclosures can often lead to a flammable hydrogen-air mixture with concentration gradients. Accidental ignition of this mixture could result in flame acceleration and deflagration-to-detonation transition (DDT). This phenomenon was experimentally investigated by Kuznetsov et al. [1,2]. They showed that flame acceleration in mixtures with concentration gradients may be determined by the maximum local hydrogen concentration in semi-confined geometries. Vollmer et al. [3,4] and Boeck et al. [5,6] reported that a strong positive effect of concentration gradients can be found on flame acceleration, especially in a channel without obstructions. In other words, concentration gradients can result in significantly stronger flame acceleration compared to the homogeneous mix...

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Shock Waves and Ablation Dynamics

Takabe

2024

Springer Series in Plasma Science and Technology

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When an intense laser is irradiated on a solid target, the laser energy is absorbed on the surface so that the material becomes plasma to expand into the vacuum region. Through the laser-plasma interaction, the laser energy heats the expanding region spreading by its sound velocity. As the result the expanding region has the temperature ~ 1 keV and the pressure reaches 100 Mbar (10TPa). Since the laser is absorbed near relatively high density (~cut-off density), the plasma can be assumed to be in LTE and hydrodynamic description is acceptable.The surface pressure called ablation pressure drives strong shock waves in the solid material as if the solid is almost gas. The shock wave physics is briefly reviewed to use the Rankin-Hugoniot (RH) relation, although detail studied is needed for the equation of state of the compressed matter. By use of the ablation pressure, it is possible to accelerate a thin material to higher velocity like a rocket propulsion.One dimensional hydrodynamics is reviewed for steady state and time dependent dynamics within the ideal fluid assumption. Deflagration and detonation waves are also explained as jump condition with energy deposition. The laser implosion dynamics is compered between stationary solutions, computational results, and the experimental data. The importance of validation of simulation codes is discussed.

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Numerical Simulation of the Deflagration-to-Detonation Transition in Inhomogeneous Mixtures

Cited by 91 publications

References 51 publications

Multi-stage nozzle-shape optimization for pulsed hydrogen–air detonation combustor

Multi-stage nozzle-shape optimization for pulsed hydrogen–air detonation combustor

Numerical simulation of flame acceleration and deflagration-to-detonation transition in hydrogen-air mixtures with concentration gradients

Shock Waves and Ablation Dynamics

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