Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session A26: Reacting Flows I: Detonation |
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Chair: J. Philip Drummond, NASA Langley Room: 321 |
Sunday, November 24, 2013 8:00AM - 8:13AM |
A26.00001: What Zeldovich did not tell us about spontaneous reaction wave propagation David R. Kassoy Zeldovich (Comb. Flame, \underline {39}, 211-214, 1980) describes a conceptual model for a ``spontaneous reaction wave'' propagating down an initially imposed negative temperature gradient in a reactive gas. The concept is based on a sequence of constant volume thermal explosions in neighboring reactant particles of lower and lower temperature \textbf{where the interaction between the particles is neglected}. This restriction prevents nonlinear gasdynamical evolution arising from the response of a compressible gas to localized, transient thermal power addition. Gu et al. (Comb. Flame, \underline {133}, 63-74, 2003) employ a nondimensional temperature gradient parameter (actually the inverse Mach number of the propagating front) to distinguished between computationally determined diverse modes of reaction front propagation arising from spherical hot spots with imposed initial negative temperature gradients in a motionless, constant pressure gas. Two questions arise from these formulations: 1. Under what conditions can such an initial state arise? 2. Can the nondimensional parameter as used by Gu et. al. be derived from a fully compressible reactive gasdynamical formulation of their problem? These questions are addressed by employing thermomechanical principles described by Kassoy (J.Eng. Math, \underline {68}, 249 -262, 2010). [Preview Abstract] |
Sunday, November 24, 2013 8:13AM - 8:26AM |
A26.00002: Pulsed Detonation Operation of an Axial Turbine David Munday, Andrew St. George, Robert Driscoll, Ephraim Gutmark A detonation is by its nature a more thermodynamically efficient combustion mode than deflagration. Several attempts are underway to integrate detonating combustion into turbomachines in order to realize the increased efficiency available, save resources and reduce emissions. One approach to this challenge is to employ pulsed detonations as from pulsed detonation engines (PDEs) and use the pulsed outflow to drive a turbine. The difficulty with this approach is that turbines, especially the more efficient axial turbines suffer in efficiency when their inflow is pulsed. At present there is not even a commonly acknowledged turbine efficiency measure which works reasonably for a pulsed input. The present work investigates the efficiency of an axial turbine with pulsed flow. Initial tests are performed with non-combusting flow in order to study the influence of pulsation on the turbine performance. This cold flow will admit a broader range of instrumentation which can be inserted within the turbine. This allows time-resolved measure of the flow angles which have a pronounced effect on the turbine performance. Later tests with detonating inflow yield global measures and these are compared to the non-combusting results. Work sponsored by Innovative Scientific Solutions, Inc. [Preview Abstract] |
Sunday, November 24, 2013 8:26AM - 8:39AM |
A26.00003: On the development of Hydrogen-air detonations Christopher Romick, Tariq Aslam, Joseph Powers The development and propagation of Hydrogen-air detonations is examined. An initially quiescent stoichiometric mixture at $298.15~K$ and $1~atm$ is initialized using a hot spot similar in character to a spark. Several two-dimensional channel widths are examined to obtain greater insight into the effect that no-slip walls have on the formation process of the detonation. To model the phenomena, the compressive, reactive Navier-Stokes equations using detailed kinetics are used with multicomponent diffusion including Soret and DuFour effects. A chemical mechanism composed of $19$ reversible reactions, containing $9$ species and $3$ elements is used for the kinetics model. The use of detailed kinetics gives rise to multiple length scales; to predict the full richness of the unsteady behavior of a detonation, all these scales must be resolved. Resolving the finest and larger scales is accomplished using the Wavelet Adaptive Multiresolution Representation (WAMR) technique. This adaptive mesh refinement technique has a high compression ratio of the number of points needed to accurately represent the flow versus an uniform grid. The time to the initial thermal explosion is examined for the various channel widths. Additionally, the long time sustainability of the detonation is studied. [Preview Abstract] |
Sunday, November 24, 2013 8:39AM - 8:52AM |
A26.00004: Analytical and Computational Study of Flame Acceleration due to Wall Friction in Combustion Tubes and Channels Berk Demirgok, V'yacheslav Akkerman Deflagration-to-detonation transition constitutes one of the fundamental problems within the studies of reacting flows. It occurs when a subsonic flamefront accelerates, with velocity jump by several orders of magnitude. According to the Shelkin model, the key element of the process is wall friction at non-slip walls, driving a flow of the fresh pre-mixture to be non-uniform, leading to a positive flame-flow feedback and thereby flame acceleration. We perform analytical and computational study of the phenomenon, with very good agreement between them in the domain of intrinsic accuracy of the theory. Theory assumes large Reynolds number (Re) and thermal expansion as well as plane-parallel flow ahead of flamefront. Simulations are performed for complete set of combustion and hydrodynamic equations. Analytical and computational results are also validated by recent experiments on ethylene-oxygen combustion. It is proven realistic flames with a large density drop at the front accelerate in a self-sustained manner and may initiate detonation in a sufficiently long tube. Before this event, the flame shape and the velocity profile remain self-similar. Acceleration rate grows with thermal expansion in the burning process but decreases with Re related to flame propagation. [Preview Abstract] |
Sunday, November 24, 2013 8:52AM - 9:05AM |
A26.00005: Spontaneous Deflagration-to-Detonation Transition in Thermonuclear Supernovae Alexei Poludnenko, Vadim Gamezo, Elaine Oran We present the analysis of the spontaneous deflagration-to-detonation transition (DDT) in turbulent thermonuclear flames in Type Ia supernovae - explosions of degenerate white dwarf stars in binary stellar systems. We show results of first-principles numerical calculations that are used to develop and validate a subgrid-scale model for predicting the onset of DDT in full-star calculations. We also discuss detailed properties of laminar thermonuclear deflagrations for compositions and densities, at which DDT is expected to occur. [Preview Abstract] |
Sunday, November 24, 2013 9:05AM - 9:18AM |
A26.00006: Boundary Layer Effects on Ignition in a Shock-Tube System Kevin Grogan, Matthias Ihme Direct numerical simulations (DNS) of an argon-diluted hydrogen/oxygen mixture are performed to study the weak and strong ignition regimes in a shock-tube system. An adaptive mesh-refinement (AMR) algorithm is used to resolve physically relevant features such as the viscous boundary layer, the shock bifurcation region, and the ignition kernels. The simulations employ a second-order accurate, nonlinear, hyperbolic equation solver that is modified to include a finite-rate kinetic mechanism, and detailed mass, thermal, and viscous diffusion transport properties. Detailed two- and three-dimensional simulations are performed to investigate effects of viscous heating, shock bifurcation, and thermo-viscous boundary layer on the ignition behavior. The locations of the ignition kernels for various post-reflected-shock conditions are studied as well as the ignition sensitivity due to the choice of thermal boundary conditions. These detailed simulations are analyzed, and correlations between observed weak and strong ignitions are compared to the ignition criterion that was proposed by Meyer and Oppenheim. [Preview Abstract] |
Sunday, November 24, 2013 9:18AM - 9:31AM |
A26.00007: Nonlinear evolution equation for 1-D pulsating detonations with Fickett's model for reactive compressible flow, Influence of $\chi$ Andre Bellerive, Justin Tang, Matei Radulescu 1-D Asymptotic analysis on Fickett's model for reactive compressible flow, i.e Burgers' equation with an added reactive term. The model's simplicity is useful to identify the mechanisms that control the detonation stability. An induction-reaction, two-step, chain-branching reaction model is used. We assume a slowed time evolution based on the particle transit through the induction zone. The equation is derived for a high activation energy and a larger exothermic reaction layer than induction layer. The evolution equation is second order in time in the shock front velocity perturbation. The equation yields both stable and unstable solutions, the unstable solutions lead to high amplitude limit-cycles. The results show the stability boundary to be the activation energy times the ratio of induction time to reaction time, $\chi |
Sunday, November 24, 2013 9:31AM - 9:44AM |
A26.00008: On the role of unreacted pockets in unstable detonation waves Jonathan Regele Pockets of unreacted fluid surrounded by combustion products form and react behind unstable detonation waves. It is unclear how the pockets interact with the detonation front and whether or not their reaction helps sustain detonation propagation. With the wide range of scales present in unstable detonations, unreasonable computational resources are required to perform direct numerical simulations that capture the complex interactions between diffusion, turbulence, and autoignition. In order to develop a basic understanding of what role these pockets may play, a simplified acoustic timescale analysis of unreacted pockets is performed to classify the behavior regimes. This classification is used to interpret experimental data and determine if the reaction of these pockets is isobaric and can be neglected or if compression or even shock waves are created. The generation of compression or shock waves suggests that these pockets may play a role in sustaining the detonation wave. [Preview Abstract] |
Sunday, November 24, 2013 9:44AM - 9:57AM |
A26.00009: A qualitative model for detonation with losses Aslan Kasimov, Luiz Faria Burgers equation with a nonlocal forcing is capable of qualitatively reproducing many dynamical characteristics of unstable detonations. We extend previous work on the model to account for generic energy losses. A new approach is proposed for solving the nonlinear eigenvalue problem associated with the steady (or quasi-steady) detonation speed. The method eliminates difficulties associated with the sonic-point singularity and allows for easy and accurate numerical solution of the problem. We explore the role of curvature or friction in the stability of a steady detonation solution and contrast our results with analogous results in the reactive Euler equations. [Preview Abstract] |
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