Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session A3: Reacting Flows: Detonations, Explosions, and DDTReacting
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Chair: Mark Short, Los Alamos National Laboratory Room: 403 |
Sunday, November 19, 2017 8:00AM - 8:13AM |
A3.00001: Numerical simulations of detonation propagation in gaseous fuel-air mixtures Praveen Honhar, Carolyn Kaplan, Ryan Houim, Elaine Oran Unsteady multidimensional numerical simulations of detonation propagation and survival in mixtures of fuel (hydrogen or methane) diluted with air were carried out with a fully compressible Navier-Stokes solver using a simplified chemical-diffusive model (CDM). The CDM was derived using a genetic algorithm combined with the Nelder-Mead optimization algorithm and reproduces physically correct laminar flame and detonation properties. Cases studied are overdriven detonations propagating through confined mediums, with or without gradients in composition. Results from simulations confirm that the survival of the detonation depends on the channel heights. In addition, the simulations show that the propagation of the detonation waves depends on the steepness in composition gradients. [Preview Abstract] |
Sunday, November 19, 2017 8:13AM - 8:26AM |
A3.00002: Simulations of Flame Acceleration and DDT in Mixture Composition Gradients Weilin Zheng, Carolyn Kaplan, Ryan Houim, Elaine Oran Unsteady, multidimensional, fully compressible numerical simulations of methane-air in an obstructed channel with spatial gradients in equivalence ratios have been carried to determine the effects of the gradients on flame acceleration and transition to detonation. Results for gradients perpendicular to the propagation direction were considered here. A calibrated, optimized chemical-diffusive model that reproduces correct flame and detonation properties for methane-air over a range of equivalence ratios was derived from a combination of a genetic algorithm with a Nelder-Mead optimization scheme. Inhomogeneous mixtures of methane-air resulted in slower flame acceleration and longer distance to DDT. Detonations were more likely to decouple into a flame and a shock under sharper concentration gradients. Detailed analyses of temperature and equivalence ratio illustrated that vertical gradients can greatly affect the formation of hot spots that initiate detonation by changing the strength of leading shock wave and local equivalence ratio near the base of obstacles. [Preview Abstract] |
Sunday, November 19, 2017 8:26AM - 8:39AM |
A3.00003: Mechanism of Gaseous Detonation Propagation Through Reactant Layers Bounded by Inert Gas Ryan Houim Vapor cloud explosions and rotating detonation engines involve the propagation of gaseous detonations through a layer of reactants that is bounded by inert gas. Mechanistic understanding of how detonations propagate stably or fail in these scenarios is incomplete. Numerical simulations were used to investigate mechanisms of gaseous detonation propagation through reactant layers bounded by inert gas. The reactant layer was a stoichiometric mixture of C$_2$H$_4$/O$_2$ at 1 atm and 300K and is 4 detonation cells in height. Cases where the inert gas temperature was 300, 1500, and 3500 K will be discussed. The detonation failed for the 300 K case and propagated marginally for the 1500 K case. Surprisingly, the detonation propagated stably for the 3500 K case. A shock structure forms that involves a detached shock in the inert gas and a series of oblique shocks in the reactants. A small local explosion is triggered when the Mach stem of a detonation cell interacts with the compressed reactants behind one of these oblique shocks. The resulting pressure wave produces a new Mach stem and a new triple point that leads to a stable detonation. Preliminary results on the influence of a deflagration at the inert/reactant interface on the stability of a layered detonation will be discussed. [Preview Abstract] |
Sunday, November 19, 2017 8:39AM - 8:52AM |
A3.00004: Numerical computation of linear instability of detonations Dmitry Kabanov, Aslan Kasimov We propose a method to study linear stability of detonations by direct numerical computation. The linearized governing equations together with the shock-evolution equation are solved in the shock-attached frame using a high-resolution numerical algorithm. The computed results are processed by the Dynamic Mode Decomposition technique to generate dispersion relations. The method is applied to the reactive Euler equations with simple-depletion chemistry as well as more complex multistep chemistry. The results are compared with those known from normal-mode analysis. [Preview Abstract] |
Sunday, November 19, 2017 8:52AM - 9:05AM |
A3.00005: Confinement Effect on Detonation Propagation in Condensed-Phase High Explosives Carlos Chiquete, Mark Short, Chad D. Meyer, James J. Quirk In applications that embed condensed-phase high explosives (HEs) in engineering scale geometries, the confining material's density and impedance have a strong influence on the resulting speed and front shape of the detonation wave in the HE. This is due to the post-shock flow divergence induced by the inert material yielding to the intense reaction zone pressures. Here, we systematically investigate this confinement effect on multi-dimensional detonation propagation. Specifically, we use a simplified HE model and stylized 2D planar and axisymmetric geometries. A shock-attached formulation of the reactive Euler equations is adopted and the post-shock flow divergence is mimicked by enforcing a (linear) boundary streamline at a prescribed deflection angle. The steady-state propagation of the wave is examined as a function of this angle including its phase velocity, detonation front pressure and the reaction zone structure. We focus on the transition from subsonic or confined flow along the boundary to supersonic flow when the detonation propagation becomes insensitive to further increases in flow divergence. [Preview Abstract] |
Sunday, November 19, 2017 9:05AM - 9:18AM |
A3.00006: Reflection Patterns Generated by Condensed-Phase Oblique Detonation Interaction with a Rigid Wall Mark Short, Carlos Chiquete, John Bdzil, Chad Meyer We examine numerically the wave reflection patterns generated by a detonation in a condensed phase explosive inclined obliquely but traveling parallel to a rigid wall as a function of incident angle. The problem is motivated by the characterization of detonation-material confiner interactions. We compare the reflection patterns for two detonation models, one where the reaction zone is spatially distributed, and the other where the reaction is instantaneous (a Chapman-Jouguet detonation). For the Chapman-Jouguet model, we compare the results of the computations with an asymptotic study recently conducted by Bdzil and Short (J. Fluid Mech. 2017) for small detonation incident angles. We show that the ability of a spatially distributed reaction energy release to turn flow streamlines has a significant impact on the nature of the observed reflection patterns. The computational approach uses a shock-fit methodology. [Preview Abstract] |
Sunday, November 19, 2017 9:18AM - 9:31AM |
A3.00007: Effects of Injection Scheme on Rotating Detonation Engine Operation Fabian Chacon, James Duvall, Mirko Gamba In this work, we experimentally investigate the operation and performance characteristics of a rotating detonation engine (RDE) operated with different fuel injection schemes and operating conditions. In particular, we investigate the detonation and operation characteristics produced with an axial flow injector configuration and semi-impinging injector configurations. These are compared to the characteristics produced with a canonical radial injection system (AFRL injector). Each type produces a different flowfield and mixture distribution, leading to a different detonation initiation, injector dynamic response, and combustor pressure rise. By using a combination of diagnostics, we quantify the pressure loses and gains in the system, the ability to maintain detonation over a range of operating points, and the coupling between the detonation and the air/fuel feed lines. We particularly focus on how this coupling affects both the stability and the performance of the detonation wave. [Preview Abstract] |
Sunday, November 19, 2017 9:31AM - 9:44AM |
A3.00008: The Physics of Thermo-mechanical Phenomena in Gases David Kassoy, Adam Norris The response of gases to transient, spatially resolved energy addition is quantified mathematically. Non-dimensional describing equations and accompanying parameters are derived and used to characterize the thermo-mechanical physics. The modeling demonstrates that the ratio of the energy addition time scale to the acoustic time scale of the affected volume, and the quantity of energy added to that volume during the former determine the characteristics of the response. Conditions appropriate to classical thermo-acoustics are identified as well as those associated with nearly isobaric and constant volume phenomena. Solutions are presented to describe the consequences of a high activation energy spatially resolved thermal explosion occurring in a reactive gas. [Preview Abstract] |
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