Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session G03: Detonations and Explosions |
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Chair: Peter Hamlington, University of Colorado Boulder Room: Georgia World Congress Center B204 |
Monday, November 19, 2018 10:35AM - 10:48AM |
G03.00001: Spontaneous Detonation Initiation in Compressible Isotropic Turbulence Colin Towery, Alexei Poludnenko, Peter Hamlington Theory and computations have shown that local hot spots in highly compressible turbulent reactive mixtures can lead to spontaneous detonation initiation. However, present theory and models are restricted to single hot spots that i) are well-separated from other local maxima in temperature; ii) are formed on timescales comparable to, or shorter than, the chemical induction and acoustic crossing times of the hot spot; and iii) evolve freely in a gas with zero initial velocity fluctuations. In this talk, by contrast, we examine detonation initiation in non-monotonic temperature fields with local maxima that are tightly spaced and evolve over a range of timescales, from an outer scale comparable to the mean induction time to a much shorter inner diffusive timescale. We perform a series of direct numerical simulations of homogeneous isotropic turbulence in reactive gas mixtures that sweep over a range turbulent Mach numbers and test both a thermally-regulated single-step Arrhenius reaction mechanism and a chain-branching-regulated detailed hydrogen-air mechanism. Although we find some evidence of spontaneous detonation initiation due to compressible turbulence, distributions of temperature-gradient magnitudes and wave propagation speeds are inconsistent with previous theory. |
Monday, November 19, 2018 10:48AM - 11:01AM |
G03.00002: Kinetic Effect of Ozone Addition on Deflagration to Detonation Transition of C_{2}H_{2}/O_{2} Mixtures in Microchannels Juan Sepulveda, Aric Rousso, Henry Ha, Timothy Chen, Wenjun Kong, Yiguang Ju The kinetic acceleration of deflagration to detonation transition (DDT) of acetylene/O_{2} mixtures at lean conditions in a 1 mm square microchannel is investigated using ozone addition. Equivalence ratios and ozone concentration were varied to understand the thermal and kinetic impacts, respectively, on DDT transition. The addition of ozone was found to drastically reduce the DDT time and onset distance via kinetic enhancement. The results showed that with a small amount of ozone addition, the DDT time was reduced by up to 77.5%, while only slightly increasing CJ velocities, by 6.7%. Moreover, the addition of 1% ozone extended the DDT limit from equivalence ratio of 0.3 to 0.2. Furthermore, it was observed that ozone addition had a much larger effect on DDT time than the increase of equivalence ratio. The present results suggested that for accelerating DDT, the kinetic effect via ozone addition is much greater than the thermal effect. |
Monday, November 19, 2018 11:01AM - 11:14AM |
G03.00003: Detonation Failure and Reinitiation Across an Inert Gap Kelsey C. Tang Yuk, XiaoCheng Mi, John H. S. Lee, Hoi Dick Ng The critical phenomena of the transmission of a gaseous detonation wave across an inert gap of finite length are computationally simulated in both one and two-dimensions. The system is modeled using the reactive Euler equations with single step Arrhenius kinetics. Downstream from the gap the detonation re-establishes the intrinsic structure corresponding to the mixture's chemical and thermodynamic properties. However, at some critical gap length the detonation fails to be reinitiated downstream. This critical length is characteristic of the reactive mixture and is related to the intrinsic length scale of the detonation. Simulations are performed over a range of reactive mixture conditions to investigate this correlation. In one-dimension the intrinsic length scale is the reaction zone length of the steady Zel'dovich-von Neumann-Döring (ZND) wave. Comparison of results in one and two-dimensions allows further investigation into the importance of cellular dynamics and multidimensional effects on the detonation reinitiation downstream. To this end, correlation with statistically determined dynamic detonation parameters such as cell size and regularity is also considered in two-dimensions. |
Monday, November 19, 2018 11:14AM - 11:27AM |
G03.00004: Effects of activation energy on the instability of oblique detonation surfaces Honghui Teng, Lin Zhou Oblique detonation waves (ODWs) are simulated using the inviscid Euler equations with one-step irreversible Arrhenius chemistry model to study effects of activation energy E_{a} on ODW surface instability. Numerical results demonstrate two types of cellular structures, one is featured by a single group of transverse waves traveling upstream, referred to as LRTW (left-running transverse waves), and the other is featured by additional RRTW (right-running transverse waves). To quantify the two destabilized processes, the first and second instability lengths are defined by the lengths of smooth surface and LRTW surface, respectively. It is found out that when E_{a} increases from 30 to 50, the first length decreases first and then keeps almost constant, while the second length decrease monotonically. By analyzing the flow structure, these variations are attributed into the change of overdriven degree. Generally, high E_{a} makes the surface unstable, but increasing E_{a} between 40 and 50, the overdriven degree increases so makes the surface stable. These two effects are opposite and then the first instability length keeps almost constant in this regime. |
Monday, November 19, 2018 11:27AM - 11:40AM |
G03.00005: Influence of Wall Shape on Steady Two-Dimensional Detonation Propagation Carlos Chiquete, Mark Short, Stephen Voelkel A characteristic path analysis is carried out for two-dimensional steady state flow using an idealized condensed-phase high explosive model for both 2D planar and axisymmetric cylindrical geometries and for both strong and weak confinement scenarios. The calculations use a specialized configuration where a solid wall is deflected to a given angle upon detonation front arrival. The characteristic paths are calculated in the hyperbolic supersonic region of the resulting flow, downstream of the sonic locus, and reveal that characteristics emanating from a supersonic section of the confining wall, for both strong and weak confinement, impinge on the sonic locus which together with the shock front bounds the detonation driving zone (the elliptic flow region which ultimately sets the velocity and front shape of the propagating detonation wave). Additionally, the imposed wall shape in this supersonic region of influence is varied to determine the ultimate effect of this flow feature on the propagation properties of the detonation wave. |
Monday, November 19, 2018 11:40AM - 11:53AM |
G03.00006: The Effect of Subsonic Confiner Flow on Detonation Propagation Mark Short, Carlos Chiquete, James Quirk A detonation consists of a shock wave driven by the gasdynamic evolution induced by chemical energy release following the shock, traveling supersonically relative to the upstream reactant state. In condensed phase explosives, the evolution of the detonation is strongly influenced by the Mach number of the flow in the inert confinement material surrounding the explosive. Typically, the detonation induces an oblique shock in the confiner. Due to the oblique configuration, the flow in the confiner can either be supersonic or subsonic along the material interface, whereas in the explosive the flow along the material interface is subsonic. Supersonic flow in the inert is moderately easy to analyze. Subsonic flow in the inert is harder due to the elliptic nature of the flow. We analyze the influence of subsonic inert flow on the dynamics of the detonation motion. This includes consideration of confiner thickness and material properties. |
Monday, November 19, 2018 11:53AM - 12:06PM |
G03.00007: Modeling Desensitization of Condensed Phase Explosives for Shock-Detonation Interactions Stephen Voelkel, Carlos Chiquete, Scott Jackson, Mark Short |
Monday, November 19, 2018 12:06PM - 12:19PM |
G03.00008: Abstract Withdrawn |
Monday, November 19, 2018 12:19PM - 12:32PM |
G03.00009: Abstract Withdrawn It has been observed that when a gas phase detonation passes through inert particle clouds the detonation can be suppressed or unaffected depending upon the cloud width, particle size and volume loading (Combustion Science and Technology 184, 406-433, 2012). On the other hand, if the particles are reactive (e.g., Aluminum) the heat release from the particle combustion could result in very different results under identical conditions. Here, we use a well established Eulerian-Lagrangian dense particle model to conduct a series of three-dimensional simulations of study the interaction of a steady ethylene/oxygen detonation with a cloud of Aluminum particles. Reduced multi-step, finite-rate kinetics for Aluminum combustion is used and the effects of particle volume fraction, size distribution and cloud width are examined to understand the behavior of the detonation coupling with reacting particles and the associated heat release. |
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