Deflagration-to-detonation transition in narrow channels: hydraulic resistance versus flame folding (original) (raw)
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On the Transition from Deflagration to Detonation in Narrow Channels
Mathematical Modelling of Natural Phenomena, 2007
A numerical study of a two-dimensional model for premixed gas combustion in a narrow, semi-infinite channel with no-slip boundary condition is performed. The work is motivated by recent theoretical advances revealing the major role of hydraulic resistance in deflagration-to-detonation transition, one of the central yet still inadequately understood phenomena of gaseous combustion. The work is a continuation and extension of recently reported results over non-isothermal boundary conditions, wider channels, and lower incipient flame velocities, closer to those of real life explosives.
Combustion Science and Technology, 2017
The entire process of deflagration-to-detonation transition (DDT) is studied through direct numerical simulations in narrow channels. Calculations with adiabatic and heat-loss boundaries are conducted to investigate the effect of heat loss to walls on flame acceleration and DDT. The numerical results show that heat loss reduces the flame acceleration rate and delays the occurrence of DDT. In the adiabatic channel, flame acceleration is caused mainly by viscosity friction with walls; ultra-fast flame in boundary layers plays a key role in the occurrence of DD. However, in the channel with heat loss the growth of the pressure pulse and the interaction of the leading shock with the boundary layers are weakened. Ultra-fast flame cannot be formed at the boundary layer in front of the flame surface and the occurrence of DDT is attributed to early burning in front of the flame.
Jurnal Teknologi, 2013
Due to complicated and rapid process, deflagration-to-detonation transition (DDT) becomes one of the major challenges in combustion theory where the exact mechanism is still poorly understood. Theoretically, the presence of obstacle may disturb flame propagation and hence make the DDT predictions more complex. Thus a comprehensive study is required to acknowledge DDT performance precisely. Lacking of information in literature causes the prediction of the transition period is still uncertain. In contrast, appropriate estimation of the DDT event is crucial for explosion safety. Thus, this present paper discusses the effect of obstacle on prediction transition deflagration to detonation event in pipeline system in order to apply an effective protection and safety systems to prevent and mitigate the gas explosion in industries. In addition the effect of bending on flame acceleration and explosion development would also be explored.
Flame acceleration in channels with obstacles in the deflagration-to-detonation transition
Combustion and Flame, 2010
It was demonstrated recently in Bychkov et al., Phys. Rev. Lett. 101 (2008) 164501, that the physical mechanism of flame acceleration in channels with obstacles is qualitatively different from the classical Shelkin mechanism. The new mechanism is much stronger, and is independent of the Reynolds number. The present study provides details of the theory and numerical modeling of the flame acceleration. It is shown theoretically and computationally that flame acceleration progresses noticeably faster in the axisymmetric cylindrical geometry as compared to the planar one, and that the acceleration rate reduces with increasing initial Mach number and thereby the gas compressibility. Furthermore, the velocity of the accelerating flame saturates to a constant value that is supersonic with respect to the wall. The saturation state can be correlated to the Chapman-Jouguet deflagration as well as the fast flames observed in experiments. The possibility of transition from deflagration to detonation in the obstructed channels is demonstrated. arXiv:1211.0655v1 [physics.flu-dyn]
Autoignition due to hydraulic resistance and deflagration-to-detonation transition
Combustion and Flame, 2008
A further development of the friction-based concept of the deflagration-to-detonation transition is presented. Employing Zeldovich's quasi-one-dimensional formulation for combustion in hydraulically resisted flows, the autoignition of the unburned gas subjected to the friction-induced precompression and preheating is assessed. It is shown that autoignition, triggering the transition, is readily attainable for quite realistic parameters.
Effects of hydraulic resistance and heat losses on detonability and flammability limits
Combustion Theory and Modelling, 2004
This paper presents an analysis of a one-dimensional combustion model capable of describing both deflagrations and detonations. Incorporating volumetric terms to account for hydraulic and thermal losses, the quenching diameters, below which each type of combustion wave cannot propagate, are calculated. The main conclusion is that, as expected, detonations have larger quenching diameters than deflagrations for sufficiently high activation energies. However, the opposite result is found for relatively low activation energies.
Physics Letters A 373 (2009) 501–510, 2009
The Letter presents analytical, numerical and experimental studies of the mechanism underlying the deflagration-to-detonation transition (DDT). Insight into how, when, and where DDT occurs is obtained by analyzing analytically and by means of multidimensional numerical simulations dynamics of a flame accelerating in a tube with no-slip walls. It is shown that the deflagration-to-detonation transition exhibits three separate stages of evolution corroborating majority experimental observations. During the first stage flame accelerates and generates shocks far ahead of the flame front. During the second stage the flame slows down, shocks are formed in the immediate proximity of the flame front and the preheated zone ahead of the flame front is created. The third stage is self-restructuring of the steep temperature profile within the flame, formation of a reactivity gradient and the actual formation of the detonation wave itself. The mechanism for the detonation wave formation, given an appropriate formation of the preheated zone, seems to be universal and involves a reactivity gradient formed from the initially steep flame temperature profile in the presence of the preheated zone. The developed theory and numerical simulations are found to be well consistent with extensive experiments of the DDT in hydrogen–oxygen and ethylene–oxygen mixtures in tubes with smooth and rough walls.
Deflagration-to-detonation transition in highly reactive combustible mixtures
Acta Astronautica, 2010
The paper presents experimental, theoretical, and numerical studies of deflagration-to-detonation transition (DDT) in highly reactive hydrogen–oxygen and ethylene–oxygen mixtures. Two-dimensional reactive Navier–Stokes equations for a hydrogen–oxygen gaseous mixture including the effects of viscosity, thermal conduction, molecular diffusion, and a detailed chemical reaction mechanism are solved numerically. It is found that mechanism of DDT is entirely determined by the features of the flame acceleration in tubes with no-slip walls. The experiments and computations show three distinct stages of the process: (1) the flame accelerates exponentially producing shock waves far ahead from the flame, (2) the flame acceleration decreases and shocks are formed directly on the flame surface, and (3) the final third stage of the actual transition to a detonation. During the second stage a compressed and heated pocket of unreacted gas adjacent ahead to the flame—the preheat zone is forming and the compressed unreacted mixture entering the flame produces large amplitude pressure pulse. The increase of pressure enhances reaction rate and due to a positive feedback between the pressure peak and the reaction the pressure peak grows exponentially, steepens into a strong shock that is coupled with the reaction zone forming the overdriven detonation wave. The proposed new physical mechanism of DDT highlights the features of flame acceleration in tubes with no-slip walls, which is the key factor of the DDT origin.
2021
The theoretical finding of the Sanal-flow-choking [PMCID: PMC7267099] and streamtube flow choking (V.R.Sanal Kumar et al., Physics of Fluids, Vol.33, No.3, 2021, DOI: 10.1063/5.0040440) are methodological advancements in predicting the deflagration-to-detonation-transition (DDT) in the real-world-fluid flows (continuum/non-continuum) with credibility. Herein, we provide a proof of the concept of the Sanal-flow-choking and streamtube-flow-choking causing DDT in wallbounded and free-external flows. Once the streamlines compacted, the considerable pressure difference attains inside the streamtube and the flow gets accelerated to the constricted region for satisfying the continuity condition set by the conservation law of nature. If the shape of the streamtube in the internal/external flow is similar to the convergent-divergent (CD) duct the phenomenon of the Sanal-flow-choking and supersonic flow development occurs at a criticaltotal-to-static pressure ratio (CPR) in yocto to yotta sca...
Gas Compression Moderates Flame Acceleration in Deflagration-to-Detonation Transition
Combustion Science and Technology, 2012
The effect of gas compression at the developed stages of flame acceleration in smooth-wall and obstructed channels is studied. We demonstrate analytically that gas compression moderates the acceleration rate and perform numerical simulations within the problem of flame transition to detonation. It is shown that flame acceleration undergoes three distinctive stages: 1) initial exponential acceleration in the incompressible regime, 2) moderation of the acceleration process due to gas compression, so that the exponential acceleration state goes over to a much slower one, 3) eventual saturation to a steady (or statistically-steady) high-speed deflagration velocity, which may be correlated with the Chapman-Jouguet deflagration speed. The possibility of deflagration-to-detonation transition is demonstrated. *vitaliy.bychkov@physics.umu.se