Flame acceleration and deflagration-to-detonation transition in narrow channels with thin obstacles

2018 ◽  
Vol 32 (29) ◽  
pp. 1850354 ◽  
Author(s):  
Jin Huang ◽  
Xiangyu Gao ◽  
Cheng Wang
Keyword(s):  
Turbulent Flame ◽  
Narrow Channels ◽  
Flame Acceleration ◽  
Deflagration To Detonation Transition ◽  
Smooth Channel ◽  
Detonation Transition ◽  
Run Up ◽  
Thin Obstacle ◽  
Strong Confinement ◽  
Small Spacing

The entire process of deflagration-to-detonation transition (DDT) in narrow channels with thin obstacle configurations is studied through high-resolution simulations. The results show that the confinement and disturbance of obstacles promote considerably the flame acceleration and DDT. There exist two modes of DDT associating with obstacle spacing S. For small spacing S, the flame acceleration depends on strong confinement and jet flow between obstacles; eventually DDT occurs due to early burning amplified by shocks in front of the flame. However, for large spacing S, the flame acceleration is mainly attributed to turbulence; DDT results from the interaction of reflection shock with turbulent flame. It is found that the run-up distance of DDT in the obstructed channels shortens significantly, as compared with that in the smooth channel.

DEFLAGRATION-TO-DETONATION TRANSITION IN A STRATIFIED SYSTEM “GASEOUS OXYGEN-LIQUID FILM OF N-DECANE”

2020 ◽  
Author(s):  
S. M. FROLOV ◽  
◽  
V. S. AKSENOV ◽  
I. O. SHAMSHIN ◽  
◽  
...  
Keyword(s):  
Liquid Film ◽  
Ignition Source ◽  
Gaseous Oxygen ◽  
Deflagration To Detonation Transition ◽  
Operation Process ◽  
Continuous Detonation ◽  
Smooth Channel ◽  
Detonation Transition ◽  
Run Up ◽  
X 24

Deflagration-to-detonation transition (DDT) in the system “gaseous oxygen- liquid film of n-decane” ' with a weak ignition source was obtained experimentally. In a series of experiments with ignition by an exploding wire that generates a weak primary shock wave (SW) with a Mach number ranging from 1.03 to 1.4, the DDT with the detonation run-up distances 1 to 4 m from the ignition source and run-up time 3 ms to 1.7 s after ignition was observed in a straight smooth channel of rectangular 54 x 24-millimeter cross section, 3 and 6 m in length with one open end. The DDT is obtained for relatively thick films with a thickness of 0. 3-0.5 mm, which corresponds to very high values of the overall fuel-to-oxygen equivalence ratios of 20-40. The registered velocity of the detonation wave (DW) was 1400-1700 m/s. In a number of experiments, a high-velocity quasi-stationary detonation-like combustion front was recorded running at an average velocity of 700-1100 m/s. Its structure includes the leading SW followed by the reaction zone with a time delay of 90 to 190 s. The obtained results are important for the organization of the operation process in advanced continuous-detonation and pulsed-detonation combustors of rocket and air-breathing engines with the supply of liquid fuel in the form of a wall film.

CFD Simulation of Deflagration to Detonation Transition for Nuclear Safety

2014 ◽  
Author(s):  
Eduardo Hwang ◽  
Felipe Porto Ribeiro ◽  
Jian Su
Keyword(s):  
Shock Wave ◽  
Power Plants ◽  
Stokes Equations ◽  
Burning Velocity ◽  
Turbulent Flame ◽  
Flame Acceleration ◽  
Turbulent Flame Speed ◽  
Combustion Models ◽  
Deflagration To Detonation Transition ◽  
Detonation Transition

The present work aims to develop an efficient methodology for evaluating the Deflagration to Detonation Transition (DDT) in accidental scenarios from inherent hydrogen risk in water-cooled NPPs (Nuclear Power Plants). The physical problem is flame acceleration through a confined geometry congested with periodic obstacles, up to formation of a travelling shock wave. The problem was modeled by the Reynolds-averaged Navier-Stokes equations (RANS) with the standard k-ε turbulence model. There are two main combustion models: EDC (Eddy Dissipation Concept) whose equations are the transport equations for chemical species involved; and BVM (Burning Velocity Model) a transport equation for reaction progress (one scalar), to be used with three available turbulent flame speed correlations (Peters, Mueller and Zimont), and a new formulation based on Piston Action of the expanding burnt gas. The present work compared characteristics of these combustion models regarding flame acceleration in the midsize mc043 experiment, in order to apply the proposed combustion model in large scale DDT simulations. Experiment mc043 is consists of igniting a 12-meter long tube with 70 annular obstacles, filled with lean hydrogen-air mixture. The numerical results revealed that the proposed model is superior to BVM model correlations in predicting shock wave formation, and may provide a computationally more efficient option to the EDC model.

scholarly journals Mechanisms and Occurrence of Detonations in Vapor Cloud Explosions

2019 ◽  
Author(s):  
Elaine Oran
Keyword(s):  
Puerto Rico ◽  
Large Scale ◽  
Ignition Source ◽  
Major Conclusion ◽  
Flame Acceleration ◽  
Deflagration To Detonation Transition ◽  
Vapor Cloud ◽  
Detonation Transition ◽  
Accidental Releases ◽  
Large Scale Tests

Not all accidental releases of flammable gases and vapors create explosions. Most releases do not find an ignition source, and of those that do ignite, most of them result in deflagrations that generate low or moderate overpressures. Under some circumstances, however, it is possible for deflagration-to-detonation transition (DDT) to occur, and this can be followed by a propagating detonation that quickly consumes the remaining detonable cloud. In a detonable cloud, a detonation creates the worst accident that can happen. Because detonation overpressures are much higher than those in a deflagration and continue through the entire detonable cloud, the damage from a DDT event is more severe.This paper first provides a brief summary of our knowledge to date of the fundamental mechanisms of flame acceleration and DDT. This information is then contrasted to and combined with evidence of detonations (detonation markers) obtained from large-scale tests and actual large vapor cloud explosions (VCEs), including events at Buncefield (UK), Jaipur (India), CAPECO (Puerto Rico), and Port Hudson (US). The major conclusion from this review is that detonations did occur in prior VCEs in at least part of the VCE accidents. Finally, actions are suggested that could be taken to minimize detonation hazards.

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