Effects of Obstacle Separation Distance on Gas Explosions: The Influence of Obstacle Blockage Ratio

Na’inna, Abdulmajid M.; Phylaktou, Herodotos N.; Andrews, Gordon E.

doi:10.1016/j.proeng.2014.10.439

Cited by 47 publications

(11 citation statements)

References 44 publications

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“…It is an important topic because DDT must be prevented in many cases [1,2] and optimized for specific applications [3][4][5]. DDT may be initiated by a number of different mechanisms that have been seen in both experiments and computations [6][7][8][9][10][11][12][13][14][15]. Not all of these mechanisms, or the interplay among them, are fully understood.…”

Section: Introductionmentioning

confidence: 99%

“…The effect of obstacles, often characterized by a blockage ratio (br, or the obstacle height divided by the channel height), on flame acceleration and DDT has been investigated experimentally [14,15] and numerically [21]. Gamezo et al [21] noted the competing effects of high blockage ratios: larger obstacles promote non-uniform flow, which leads to fast flame acceleration and they also weaken shocks diffracting over large obstacles.…”

Section: Introductionmentioning

confidence: 99%

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Shock transition to detonation in channels with obstacles

Goodwin

Houim

Oran

2017

Proceedings of the Combustion Institute

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Multidimensional numerical simulations of an unconfined, homogeneous, chemically reactive gas were used to study interactions leading to deflagration-to-detonation transition (DDT). The configuration studied was a long rectangular channel with regularly spaced obstacles containing a stoichiometric mixture of ethylene and oxygen, initially at atmospheric conditions and ignited in a corner with a small flame. The compressible reactive Navier-Stokes equations were solved by a high-order numerical algorithm on a locally adapting mesh. The initial laminar flame develops into a turbulent flame with the creation of shocks, shock-flame interactions, shock-boundary layer interactions, and a host of fluid and chemical-fluid instabilities. The final result may be eventual deflagration-to-detonation transition (DDT). Here two types of simulations are described, one with DDT occurring in a gradient of reactivity, which is common in the channels with higher obstacles, and another in which DDT arises from energy focusing as shocks converge. For the latter case, the rate of energy deposition necessary to initiate a detonation in the unburned gas is analyzed using a control volume analysis.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Shock transition to detonation in channels with obstacles

Goodwin

Houim

Oran

2017

Proceedings of the Combustion Institute

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“…The effect of obstacles, often characterized by a blockage ratio (br, or the obstacle height divided by the channel height), on flame acceleration and DDT has been investigated numerically [21] and experimentally [14,15]. Gamezo et al [21] noted the competing effects of high blockage ratios: larger obstacles promote nonuniform flow, which leads to rapid flame acceleration, and they also weaken shocks diffracting over large obstacles.…”

mentioning

confidence: 99%

Effect of decreasing blockage ratio on DDT in small channels with obstacles

Goodwin

Houim

Oran

2016

Combustion and Flame

111

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Multidimensional numerical simulations of an unconfined, homogeneous, chemically reactive gas were used to catalog interactions leading to the deflagration-to-detonation transition (DDT). The configuration studied was an infinitely long rectangular channel with regularly spaced obstacles containing a stoichiometric mixture of ethylene and oxygen, initially at atmospheric conditions and ignited in a corner with a small flame. The channel height is kept constant at 3200 µm and obstacle heights varied from 2560 µm to 160 µm to decrease the blockage ratio (br) from 0.8 to 0.05. The compressible reactive Navier-Stokes equations were solved by a high-order numerical algorithm on a locally adapting grid.The initially laminar flame develops into a turbulent flame with the creation of shocks, shock-flame interactions, shock-boundary layer interactions, a host of fluid and chemical-fluid instabilities, and DDT.Several different DDT mechanisms are observed as the br is reduced. For br in the range of 0.5 to 0.35, the shocks in the unburned material diffract over the obstacles and reflect against the channel wall, forming Mach stems that increase in strength with every obstacle traversed. Eventually, the Mach stem strength is sufficient for the unburned mixture to detonate after it reflects from an obstacle. For br outside of this range, DDT may occur either through Mach-stem reflection or through direct initiation due to shock focusing. Stochasticity of the turbulence leading to DDT in channels with low br is considered.

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“…In turbulent explosions, the maximum burning rate, and therefore the highest rate of pressure generation for a given vent size, will occur at the position of maximum turbulence intensity. It has been shown (Baines & Peterson, 1951;Na'inna et al, 2014), that the turbulence intensity increases downstream of an obstacle array until it reaches a maximum value some distance after it, and it then begins to decay at an approximately steady rate over a relatively long distance. Consequently, if a flame front is propagating towards a series of obstacle arrays, the maximum flame speed, and hence overpressure, might be generated if the arrays were separated by the 'critical' distance; that is, each successive array is located just downstream of the position of maximum turbulence intensity, so that it receives the flame front at its peak speed, and thereby, it generates the maximum possible turbulence intensity downstream, so that the peak flame speed is received by the next obstacle, and so on.…”

Section: Effect Of Area Blockage and Pitchmentioning

confidence: 99%

The effect of vent size and congestion in large-scale vented natural gas/air explosions

Tomlin

Johnson

Cronin

et al. 2015

Journal of Loss Prevention in the Process Industries

103

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A typical building consists of a number of rooms; often with windows of different size and failure pressure and obstructions in the form of furniture and décor, separated by partition walls with interconnecting doorways. Consequently, the maximum pressure developed in a gas explosion would be dependent upon the individual characteristics of the building. In this research, a large-scale experimental programme has been undertaken at the DNV GL Spadeadam Test Site to determine the effects of vent size and congestion on vented gas explosions. Thirtyeight stoichiometric natural gas/air explosions were carried out in a 182 m 3 explosion chamber of L/D = 2 and K A = 1, 2, 4 and 9. Congestion was varied by placing a number of 180 mm diameter polyethylene pipes within the explosion chamber, providing a volume congestion between 0 and 5% and cross-sectional area blockages ranging between 0 and 40%. The series of tests produced peak explosion overpressures of between 70 mbar and 3.7 bar with corresponding maximum flame speeds in the range 35 -395 m/s at a distance of 7 m from the ignition point. The experiments demonstrated that it is possible to generate overpressures greater than 200 mbar with volume blockages of as little as 0.57%, if there is not sufficient outflow through the inadvertent venting process. The size and failure pressure of potential vent openings, and the degree of congestion within a building, are key factors in whether or not a building will sustain structural damage following a gas explosion. Given that the average volume blockage in a room in a UK inhabited building is in the order of 17%, it is clear that without the use of large windows of low failure pressure, buildings will continue to be susceptible to significant structural damage during an accidental gas explosion.

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Effects of Obstacle Separation Distance on Gas Explosions: The Influence of Obstacle Blockage Ratio

Cited by 47 publications

References 44 publications

Shock transition to detonation in channels with obstacles

Shock transition to detonation in channels with obstacles

Effect of decreasing blockage ratio on DDT in small channels with obstacles

The effect of vent size and congestion in large-scale vented natural gas/air explosions

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