Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session G26: Reacting Flows: Experiments I |
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Chair: Mark Short, Los Alamos National Laboratory Room: E146 |
Monday, November 21, 2016 8:00AM - 8:13AM |
G26.00001: Dynamics of Detonation Propagation in Two-Dimensional Curved Geometries Mark Short, James Quirk, Carlos Chiquete, Chad Meyer A detonation is a complex, compressible flow-reaction driven structure consisting of a lead shock wave and subsequent reaction zone in which reactants are converted into products. In condensed-phase explosives, the generated high pressures lead to yielding of confinement, and detonation reaction zone structure becomes multidimensional. The detonation structure and speed is then determined by a complex interaction between streamline divergence, compressibility and reaction. Curved geometries are important for understanding the effects of geometry on the compressible-reactive flow mechanisms of detonation propagation, as it includes elements of shock diffraction, flow divergence and boundary interactions. Here, we study this complex compressible flow evolution in two-dimensional curved geometries, highlighting the relation between the detonation motion and induced curvature of the detonation front. [Preview Abstract] |
Monday, November 21, 2016 8:13AM - 8:26AM |
G26.00002: Body-Fitted Detonation Shock Dynamics and the Pseudo-Reaction-Zone Energy Release Model Chad Meyer, James Quirk, Mark Short, Carlos Chqiuete Programmed-burn methods are a class of models used to propagate a detonation wave, without the high resolution cost associated with a direct numerical simulation. They separate the detonation evolution calculation into two components: timing and energy release. The timing component is usually calculated with a Detonation Shock Dynamics model, a surface evolution representation that relates the normal velocity of the surface $(D_{n})$ to its local curvature. The energy release component must appropriately capture the degree of energy change associated with chemical reaction while simultaneously remaining synchronized with the timing component. The Pseudo-Reaction-Zone (PRZ) model is a reactive burn like energy release model, converting reactants into products, but with a conversion rate that is a function of the DSD surface $D_{n}$ field. As such, it requires the DSD calculation produce smooth $D_{n}$ fields, a challenge in complex geometries. We describe a new body-fitted approach to the Detonation Shock Dynamics calculation which produces the required smooth $D_{n}$ fields, and a method for calibrating the PRZ model such that the rate of energy release remains as synced as possible with the timing component. We show results for slab, rate-stick and arc geometries. [Preview Abstract] |
Monday, November 21, 2016 8:26AM - 8:39AM |
G26.00003: Shock Polar Angles and Confinement Effect on Detonation Propagation Carlos Chiquete, Mark Short, Chad Meyer, James Quirk, John Bdzil In high explosive (HE) engineering applications, the shape of a detonation front is influenced by the density and impedance of the inert material that surrounds the explosive. Where the detonation shock intersects the material boundary, a number of gasdynamic reflection patterns are possible involving shocks, Prandtl-Meyer fans and material interfaces. To leading-order, these reflection patterns can be predicted through a shock polar analysis. For the commonly used Detonation Shock Dynamics (DSD) front surface propagation model, the shape and evolution of the detonation wave is determined by the specification of the surface wave angle at the HE charge-confiner interface. Typically, the shock polar analysis is employed to approximate this necessary ``edge angle" using specified equations of state for the HE-inert pair and a given phase velocity. For engineering applications, we need to evaluate how accurately a shock polar analysis can predict the DSD model edge-angle. We extend previous on this issue examining reactive flow simulations of detonation propagation in a confined HE compared to the predictions of a shock polar analysis. [Preview Abstract] |
Monday, November 21, 2016 8:39AM - 8:52AM |
G26.00004: Effect of fuel stratification on detonation wave propagation Damien Masselot, Romain Fievet, Venkat Raman Rotating detonation engines (RDEs) form a class of pressure-gain combustion systems of higher efficiency compared to conventional gas turbine engines. One of the key features of the design is the injection system, as reactants need to be continuously provided to the detonation wave to sustain its propagation speed. As inhomogeneities in the reactant mixture can perturb the detonation wave front, premixed fuel jet injectors might seem like the most stable solution. However, this introduces the risk of the detonation wave propagating through the injector, causing catastrophic failure. On the other hand, non-premixed fuel injection will tend to quench the detonation wave near the injectors, reducing the likelihood of such failure. Still, the effects of such non-premixing and flow inhomogeneities ahead of a detonation wave have yet to be fully understood and are the object of this study. A 3D channel filled with O$_2$ diluted in an inert gas with circular H$_2$ injectors is simulated as a detonation wave propagates through the system. The impact of key parameters such as injector spacing, injector size, mixture composition and time variations will be discussed. [Preview Abstract] |
Monday, November 21, 2016 8:52AM - 9:05AM |
G26.00005: Fast Hydrogen-Air Flames for Turbulence Driven Deflagration to Detonation Transition Jessica Chambers, Kareem Ahmed Flame acceleration to Detonation produces several combustion modes as the Deflagration-to-Detonation Transition (DDT) is initiated, including fast deflagration, auto-ignition, and quasi-detonation. Shock flame interactions and turbulence levels in the reactant mixture drive rapid flame expansion, formation of a leading shockwave and post-shock conditions. An experimental study to characterize the developing shock and flame front behavior of propagating premixed hydrogen-air flames in a square channel is presented. To produce each flame regime, turbulence levels and flame propagation velocity are controlled using perforated plates in several configurations within the experimental facility. High speed optical diagnostics including Schlieren and Particle Image Velocimetry are used to capture the flow field. In-flow pressure measurements acquired post-shock, detail the dynamic changes that occur in the compressed gas directly ahead of the propagating flame. Emphasis on characterizing the turbulent post-shock environment of the various flame regimes helps identify the optimum conditions to initiate the DDT process. The study aims to further the understanding of complex physical mechanisms that drive transient flame conditions for detonation initiation. [Preview Abstract] |
Monday, November 21, 2016 9:05AM - 9:18AM |
G26.00006: Experimental Study on Dynamics of 2H$_{\mathrm{2}}$/O$_{\mathrm{2}}$/2Ar Detonations with a Constant Mass Divergence Qiang Xiao, Jiaxin Chang, Maxime La Fleche, Matei I. Radulescu Very recently, Borzou and Radulescu (2016) formulated a novel solution allowing for an easy and precise quantification of loss effects during detonation propagation involving an exponentially shaped channel. ~They found that the detonation dynamics departed from the ZND model predictions, particularly for very unstable detonations. ~The question arises if the ZND model can predict the dynamics of much less unstable mixtures, in spite of the presence of a cellular structure. ~The present study focuses on a more stable mixture of 2H$_{\mathrm{2}}$/O$_{\mathrm{2}}$/2Ar with better known reaction kinetics.~The results obtained experimentally for the velocity deficit in terms of the amount of mass divergence were found in excellent agreement with the predictions made with the ZND model, in spite of the detonation reaction zone being organized in strong cellular structures with reactive transverse waves. ~ [Preview Abstract] |
Monday, November 21, 2016 9:18AM - 9:31AM |
G26.00007: Acquisition of high-fidelity flyer characteristics using PDV and streak imaging Joseph Olles, Ryan Wixom, J. Patrick Ball, Graham Kosiba Acquisition of experimental flight characteristics of electrically driven flyers (EDFs) is important in understanding the flyer's role in initiating detonator explosives. The velocity throughout a plastic flyer's flight was measured, as well as the magnitude and duration of the impulse while impacting an acrylic window. Despite the small size, thickness, and large accelerations of the EDFs, diagnostic techniques now have the temporal and spatially fidelity to measure validation-quality flyer characteristics. Using multipoint photonic Doppler velocimetry (PDV) in conjunction with streak imaging through a fiber array the velocity profile, bow shock (air cushion), time of impact, flyer shape at impact, and shock duration were measured. Shock physics simulations were then compared to this high fidelity data as a means of validating equations of state. Through the combination of experiments and simulations we can achieve a greater fundamental understanding of the energy transfer from the EDF to the energetic material prior to initiation. [Preview Abstract] |
Monday, November 21, 2016 9:31AM - 9:44AM |
G26.00008: Analysis of Porous Media as Inlet Concept for Rotating Detonation Engines Kevin Grogan, Matthias Ihme Rotating detonation engines combust reactive gas mixtures with a high-speed, annularly-propagating detonation wave, which provides many advantages including a stagnation pressure gain and a compact, lightweight design. However, the optimal design of the inlet to the combustion chamber inlet is a moot topic since improper design can significantly reduce detonability and increase pressure losses. The highly diffusive properties of porous media could make it an ideal material to prevent the flashback of the detonation wave and therefore, allow the inlet gas to be premixed. Motivated by this potential, this work employs simulation to evaluate the application of porous media to the inlet of a rotating detonation engine as a novel means to stabilize a detonation wave while reducing the pressure losses incurred by non-ideal mixing strategies. [Preview Abstract] |
(Author Not Attending)
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G26.00009: NOx Emissions from a Rotating Detonation-wave Engine. Kazhikathra Kailasanath, Douglas Schwer Rotating detonation-wave engines (RDE) are a form of continuous detonation-wave engines. They potentially provide further gains in performance than an intermittent or pulsed detonation--wave engine (PDE). The overall flow field in an idealized RDE, primarily consisting of two concentric cylinders, has been discussed in previous meetings. Because of the high pressures involved and the lack of adequate reaction mechanisms for this regime, previous simulations have typically used simplified chemistry models. However, understanding the exhaust species concentrations in propulsion devices is important for both performance considerations as well as estimating pollutant emissions. Progress towards addressing this need will be discussed in this talk. In this approach, an induction parameter model is used for simulating the detonation but a more detailed finite-chemistry model including NOx chemistry is used in the expansion flow region, where the pressures are lower and the uncertainties in the chemistry model are greatly reduced. Results show that overall radical concentrations in the exhaust flow are substantially lower than from earlier predictions with simplified models. Results to date show that NOx emissions are not a problem for the RDE due to the short residence times and the nature of the flow field. Furthermore, simulations show that the amount of NOx can be further reduced by tailoring the fluid dynamics within the RDE. [Preview Abstract] |
Monday, November 21, 2016 9:57AM - 10:10AM |
G26.00010: A stabilization mechanism for the low-velocity gaseous detonations with losses Aslan Kasimov, Aliou Sow, Roman Semenko Using the reactive Euler equations, we investigate numerically the nonlinear stability of steady-state one-dimensional gaseous detonations in the presence of both momentum and heat losses. Our results point to a possible stabilization mechanism for the low-velocity detonations in such systems. The mechanism stems from the existence of a one-parameter family of steady-state solutions found in Semenko et al. \textit{Shock Waves}, 26(2), 141-160, 2016. [Preview Abstract] |
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