On the possibility of non-dimensionalizing DDT limits and distances (original) (raw)
Related papers
Detonation Transition in Relatively Short Tubes
30th International Symposium on Shock Waves 1. Springer, Cham. Pages 481-485, 2017
Experimental data and numerical simulations on flame acceleration, shock-flame interaction and deflagration-to-detonation transition mechanism for stoichiometric hydrogen-oxygen mixtures at reduced pressure in relatively short tubes have been analysed. It was shown that the detonation occurs as a result of multiple reflections of precursor shock wave and its interaction with the flame. Adiabatic compression and heating of unreacted gas a front of the flame together with flame surface increase due to the Richtmyer-Meshkov instability provide preconditioning of the DDT process. Several times higher pressure, temperature and reaction rate within a preconditioning zone leads to significant decrease of run-up-distance to DDT in relatively short tubes. Results of the work will provide detailed information on multiple shock - flame interactions leading to the DDT process for numerical code validations.
2011
The problem of the deflagration-to-detonation transition (DDT) and a key role of shock waves, boundary layer and turbulence in the detonation preconditioning process is well known but still not resolved in the combustion theory. The ignition, flame propagation with a flow ahead of the flame, and shock waves generation with turbulent boundary layer behind the shock is the sequence of principal events leading to the deflagration-to-detonation transition in smooth channels [1-3]. As Ya. Zeldovich wrote [4], the turbulence is not only one and even not the major reason of the flame acceleration in smooth channels. Wrinkled flame stretch and non-uniformity of the flow across the channel can be the main reason of flame acceleration leading to DDT. Experimental schlieren photos indicated that location of the transition to detonation always originates somewhere within the shockwave complex, sometimes near the wall in the boundary layer, sometimes in the center of a channel. One of the main p...
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...
Non-dimensionalized distances and limits for the transition of deflagration to detonation
Shock Waves
This experimental work investigates the possibility to non-dimensionalize the limits and the distances of the Deflagration-to-Detonation-Transition process (DDT). The deflagration was ignited using jets of hot gases generated by the impact of a Chapman-Jouguet detonation on a multi-perforated plate. Small holes were uniformly distributed on the plate, over the whole tube section. The tube was 1-m long with square cross-section 40 × 40 mm 2. The reactive mixtures were the stoichiometric compositions of hydrogen, methane and oxygen (1-x)H 2 + x CH 4 + 1 2 (1 + 3 x)O 2 with the composition parameter x ranging from 0 to 1. The initial pressure p 0 was varied from 12 to 35 kPa, and the initial temperature was 294 K. The re-ignition conditions and distances were obtained as functions of x, p 0 and the plate properties. The mean widths of the detonation cells measured at the wall were used to nondimensionalize the DDT distances, the surface of the perforations and the surface of the walls of the plate holes. This non-dimensional DDT distance thus appears to be a concave increasing function of the non-dimensional perforated surface independent of the regularity of the cellular structure. DDT processes are very dependent on the system configuration and the ignition conditions but our analysis suggests that the proper selection of non-dimensional numbers built from the system characteristics can help in anticipating the corresponding DDT limits and distances to a reasonable approximation.
Chapman–Jouguet deflagrations and their transition to detonation
Proceedings of the Combustion Institute, 2017
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.
On the dynamics of multi-dimensional detonation
Journal of Fluid Mechanics, 1996
We present an asymptotic theory for the dynamics of detonation when the radius of curvature of the detonation shock is large compared to the one-dimensional, steady, Chapman-Jouguet (CJ) detonation reaction-zone thickness. The analysis considers additional time-dependence in the slowly varying reaction zone to that considered in previous works. The detonation is assumed to have a sonic point in the reactionzone structure behind the shock, and is referred to as an eigenvalue detonation. A new, iterative method is used to calculate the eigenvalue relation, which ultimately is expressed as an intrinsic, partial differential equation (PDE) for the motion of the shock surface. Two cases are considered for an ideal equation of state. The first corresponds to a model of a condensed-phase explosive, with modest reaction rate sensitivity, and the intrinsic shock surface PDE is a relation between the normal detonation shock velocity, D,, the first normal time derivative of the normal shock velocity, D,,, and the shock curvature, IC. The second case corresponds to a gaseous explosive mixture, with the large reaction rate sensitivity of Arrhenius kinetics, and the intrinsic shock surface PDE is a relation between the normal detonation shock velocity, D,, its first and second normal time derivatives of the normal shock velocity, b,, B,, and the shock curvature, IC, and its first normal time derivative of the curvature, k. For the second case, one obtains a one-dimensional theory of pulsations of plane CJ detonation and a theory that predicts the evolution of self-sustained cellular detonation. Versions of the theory include the limits of near-CJ detonation, and when the normal detonation velocity is significantly below its CJ value. The curvature of the detonation can also be of either sign, corresponding to both diverging and converging geometries.
Flame Acceleration and DDT in a Torus Geometry
Kuznetsov M., Yanez J., Grune J. (2017) Flame Acceleration and DDT in a Torus Geometry. In: Ben-Dor G., Sadot O., Igra O. (eds) 30th International Symposium on Shock Waves 1. Springer, Cham, 2017
A series of combustion experiments in an optically transparent annular channel were carried out with hydrogenoxygen mixtures from 15 to 85 vol.% H2. The complex formed by an oblique shock wave and a subsonic deflagration, only recently observed by the authors in an annular channel is investigated. The ensemble has the notable property of propagating with the Chapman-Jouguet velocity up to 3000 m/s in the circumferential direction being of intrinsic subsonic nature. The structure is discussed in detail utilizing an algebraic approach to provide an insight of the apparently contradictory experimental observation of a deflagration which propagates with its Chapman-Jouguet velocity.
The results of experimental studies during which transition to detonation events occurred are presented. These observations and their interpretation are then discussed, and the conditions for the onset of detonation are described, with particular attention paid to the nature of the deflagration to detonation transition (DDT)phenomena. The resulting implications for predicting detonation evolution using computational fluid dynamic methods in practical applications are also discussed.
Towards non-dimensionalized distances and limits for transition of deflagration to detonation
HAL (Le Centre pour la Communication Scientifique Directe), 2021
This experimental work investigates the possibility to non-dimensionalize the limits and the distances of the Deflagration-to-Detonation-Transition process (DDT). The deflagration was ignited using jets of hot gases generated by the impact of a Chapman-Jouguet detonation on a multi-perforated plate. Small holes were uniformly distributed on the plate, over the whole tube section. The tube was 1-m long with square cross-section 40 × 40 mm 2. The reactive mixtures were the stoichiometric compositions of hydrogen, methane and oxygen (1-x)H 2 + x CH 4 + 1 2 (1 + 3 x)O 2 with the composition parameter x ranging from 0 to 1. The initial pressure p 0 was varied from 12 to 35 kPa, and the initial temperature was 294 K. The re-ignition conditions and distances were obtained as functions of x, p 0 and the plate properties. The mean widths of the detonation cells measured at the wall were used to nondimensionalize the DDT distances, the surface of the perforations and the surface of the walls of the plate holes. This non-dimensional DDT distance thus appears to be a concave increasing function of the non-dimensional perforated surface independent of the regularity of the cellular structure. DDT processes are very dependent on the system configuration and the ignition conditions but our analysis suggests that the proper selection of non-dimensional numbers built from the system characteristics can help in anticipating the corresponding DDT limits and distances to a reasonable approximation.