Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 54, Number 19
Sunday–Tuesday, November 22–24, 2009; Minneapolis, Minnesota
Session EM: Reacting Flows II |
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Chair: Gary Settles, Pennsylvania State University Room: 200B |
Sunday, November 22, 2009 4:15PM - 4:28PM |
EM.00001: Laboratory-scale experiments to determine explosive properties using spherical concentric composite explosives Matthew Biss, Gary Settles Laboratory-scale air-blast experiments using gram-range composite explosive charges are presented. Composite charges consist of a spherical booster charge surrounded by a concentric spherical ``candidate material'' charge in the form of a shell. Air-blast explosive tests are conducted to measure the radius vs. time of the explosively-driven shock wave using digital high-speed shadowgraphy. Profiles of peak shock wave pressure vs. radius are then found using the Rankine-Hugoniot relationship for both the booster alone and the composite charges. Using calculated peak shock wave pressures, a procedure is developed to remove the booster effects from the signature produced by the composite charge, yielding the peak shock wave pressure effect due to the candidate explosive material alone. By this means we demonstrate the ability to properly characterize, at the laboratory scale with a few grams of explosive, insensitive explosive materials that require a booster charge for detonation. This characterization yields TNT equivalence and other useful explosive properties. [Preview Abstract] |
Sunday, November 22, 2009 4:28PM - 4:41PM |
EM.00002: Laboratory-scale blast testing of materials using air-shock loading Forrest Svingala, Matthew Biss, Michael Hargather, Gary Settles The deformation of materials due to near-field explosions is a complex topic with many military and anti-terrorism applications. Typical explosive blast testing is conducted on large ballistic ranges using several kilograms of explosives, at a high cost, and with limited instrumentation. We have developed a range of experimental techniques for performing explosive blast research in the laboratory using gram-range explosive charges. Here we present recent measurements of the deformation of aluminum panels subjected to a range of explosive blast impulses. Through an explosive characterization procedure the blast impulse produced by a charge is known a priori. Our approach then couples the known explosion energy to the aluminum panels via shock wave propagation through the air. Time-resolved three-dimensional motion of the panel surface response is directly measured via stereoscopic high-speed digital image correlation. The data are used to compare material deformation characteristics to explosive loading parameters. These laboratory techniques can be used for validation of computational simulations and to develop high-strain rate material strength models. Ultimately results from these gram-range tests can be scaled to predict full-scale blast response characteristics. [Preview Abstract] |
Sunday, November 22, 2009 4:41PM - 4:54PM |
EM.00003: Planar Laser Induced Fluorescence of Shock Initiated Combustion of a Spherical Density Inhomogeneity Nicholas Haehn, Chris Weber, Jason Oakley, Mark Anderson, Dave Rothamer, Riccardo Bonazza A spherical density inhomogeneity with a stoichiometric mixture of H$_{2}$, O$_{2}$, and a diluent such as Xe is ignited with a planar shock wave. When a heavy bubble, such as Xe, is shock accelerated in a lighter ambient gas, such as Ar, the shock wave at the exterior periphery of the bubble travels faster than the interior transmitted wave, resulting in shock-focusing at the downstream pole of the bubble. The shock wave convergence results in a temperature much higher than the one behind the transmitted shock and auto ignition may occur at this location. For non-point source ignition experiments, the temperature is raised by a second shock acceleration from the planar shock that reflects from the shock tube's end-wall. These experiments shed light on the combustion characteristics under both turbulent and non-turbulent conditions. In addition, results are used for validating hydrodynamic codes with chemical reactions. The experiments are performed at the Wisconsin Shock Tube Laboratory in a 6 m vertical shock tube with a 25.4$\times $25.4 cm$^{2}$ square cross-section. Diagnostics are performed using planar laser induced fluorescence of the OH$^{-}$ molecule present during the combustion process. A Nd:Yag pumped dye laser at a wavelength of 283 nm excites the (1,0) band of the OH$^{-}$ molecule. [Preview Abstract] |
Sunday, November 22, 2009 4:54PM - 5:07PM |
EM.00004: Modeling Unit Cell interactions for the Microstructure of a Heterogeneous Explosive: Detonation Diffraction Past an Inert Sphere D. Scott Stewart, John B. Bdzil We describe an approach to model multi-phase blast explosive, which is primarily condensed y volume with inert embedded particles. The asymptotic theory of detonation shock dynamics governs the detonation shock propagation in the explosive. The detonation shock moves at a normal speed that depends on the shock curvature. The shock angle with the particle boundary is also prescribed. We describe theory to predict the behavior of a collection of such detonation shock/particle interactions in the larger aggregate. A unit cell problem, of a detonation shock diffracting over a sphere, is analyzed by analytical and numerical means. The properties of an ensemble of such unit cell problems are discussed with implications for the macroscopic limiting behavior of the heterogeneous explosive. [Preview Abstract] |
Sunday, November 22, 2009 5:07PM - 5:20PM |
EM.00005: Axisymmetric Shock-Attached Frame Detonation Simulations Brian Taylor, Aslan Kasimov, D. Scott Stewart We present a method of simulating one-dimensional axisymmetric detonations governed by the reactive Euler equations in a reference frame moving with the shock surface. We use this methodology to verify relations between normal detonation speed, $D_n$, and curvature, ($\kappa$), as predicted by Detonation Shock Dynamics (DSD), an asymptotic theory derived in the limit of slowly varying, weakly curved detonations. Our simulations demonstrate the previously theorized instability of certain regions of $D_n$-$\kappa$ solutions with multiple turning points, which result in rapid transition to strong detonation or failure of the reaction front. It is also shown that the shock-attached frame method can be used to obtain $D_n$-$\kappa$ relations that satisfy the complete reactive Euler equations without restrictions to small curvature or near Chapman-Jouguet detonation speeds. [Preview Abstract] |
Sunday, November 22, 2009 5:20PM - 5:33PM |
EM.00006: Explosive, Spatially Distributed, Time Resolved Thermal Energy Deposition into a Finite Gas Volume David R. Kassoy Add thermal energy quickly to a finite volume of gas. Kaboom!! How much? How fast? An asymptotics-based analysis of the Navier-Stokes equations is used to study the response of a finite gas volume (length scale R') to spatially distributed, time resolved energy deposition per unit mass (characterized by q$_{R}$') on a specific time scale (t$_{H}$') short compared to the initial acoustic time of the volume (t$_{A}$'=R'/a$_{0}$'), where a$_{0}$'=$\surd \gamma $R'T$_{0}$ is the initial acoustic speed) such that t$_{H}$'/ t$_{A}$'=$\varepsilon <<$1. The initial state is described by (T$_{0}$',p$_{0}$',$\rho _{0}$'), and speed zero. The energy deposition is related to the initial internal energy by q$_{R}$'= [a$_{0}$']$^{2}$/$\alpha $ where $\alpha \le $1, compatible with a characteristic temperature rise in the heated spot $\Delta $T'/T$_{0}$'=O(1/$\alpha )$. Ephemeral inertial confinement prevails when $\varepsilon ^{2}<<\alpha <<$1, characterized by pressure rising with temperature because the density change and internal Mach number are both very small. Alternatively, when the energy addition reaches a critically large amount, $\alpha =\varepsilon ^{2}$, the heat addition process is fully compressible and the internal Mach number reaches sonic values. One can apply these scaling concepts to explain the spontaneous appearance of hot spots observed in detonation initiation processes and the associated gasdynamic wave generation [Preview Abstract] |
Sunday, November 22, 2009 5:33PM - 5:46PM |
EM.00007: A two-phase micromorphic model for compressible granular materials Samuel Paolucci, Weiming Li, Joseph Powers We introduce a new two-phase continuum model for compressible granular material based on micromorphic theory and treat it as a two-phase mixture with inner structure. By taking an appropriate number of moments of the local micro scale balance equations, the average phase balance equations result from a systematic averaging procedure. In addition to equations for mass, momentum and energy, the balance equations also include evolution equations for microinertia and microspin tensors. The latter equations combine to yield a general form of a compaction equation when the material is assumed to be isotropic. When non-linear and inertial effects are neglected, the generalized compaction equation reduces to that originally proposed by Bear and Nunziato. We use the generalized compaction equation to numerically model a mixture of granular high explosive and interstitial gas. One-dimensional shock tube and piston-driven solutions are presented and compared with experimental results and other known solutions. [Preview Abstract] |
Sunday, November 22, 2009 5:46PM - 5:59PM |
EM.00008: Combined Space and Time Adaptivity Using the WAMR/G-Scheme Method Zachary Zikoski, Samuel Paolucci, Mauro Valorani Adaptive methods in CFD allow for savings in execution time by reducing the number of unknowns solved for at each computational step. The Wavelet Adaptive Multiresolution Representation (WAMR) provides spatial adaptivity which automatically supplies grid resolution based on the local demands of the solution itself. Likewise, the G-Scheme framework applies a similar capability in time. A system of ODEs can be ordered and separated into subsets of ``fast'' or near-equilibrium modes, ``slow'' or frozen modes, and ``active'' intermediate modes. Only the active modes are integrated, with asymptotics accounting for the contributions of the slow and fast dynamics. The pairing of spatial adaptivity using the WAMR method and temporal adaptivity using the G-Scheme allows for a substantial reduction in space-time degrees of freedom needed. The combined WAMR/G-scheme method is applied to several problems including reactive, compressible flow simulations. [Preview Abstract] |
Sunday, November 22, 2009 5:59PM - 6:12PM |
EM.00009: Simulations of Reacting Flow using Spectral Deferred Corrections Candace Gilet, Ann Almgren, John Bell, Marcus Day, Mike Lijewski, Michael Minion Numerical simulations of reacting flows frequently require capturing advection, diffusion, and reaction processes, which can have time scales that differ widely. When a fully explicit method is used the time step is controlled by the fastest process. This can result in calculations requiring so many time steps that the computational cost becomes prohibitively large. Fully implicit methods allow a larger time step, but require the simultaneous solution of (typically nonlinear) equations, again leading to restrictively high computational costs. Operator slitting methods allow for the use of a mix of implicit and explicit methods; however the splitting errors can be so large that prohibitively small time steps are still needed. An alternative to operator splitting is a class of methods called Spectral Deferred Corrections (SDC). The idea behind SDC methods is to represent temporal evolution of the system as an integral in time and develop algorithms that iteratively couple the different physical processes, thus reducing the splitting error. This work explores the use of SDC methodology in two-dimensional simulations of reacting flows with realistic chemistry. The results from simulations using SDC are presented and their performance is compared with that of Strang splitting. [Preview Abstract] |
Sunday, November 22, 2009 6:12PM - 6:25PM |
EM.00010: Modeling non-unity Lewis number effects in premixed flames Guillaume Blanquart, Ed Knudsen, Heinz Pitsch The combustion of hydrogen in Low Swirl Burners (LSB) is considered as an alternative for power production for it is characterized by low emissions and high efficiency. However, lean hydrogen premixed flames are subject to thermo-diffusive instabilities induced by the large diffusivity of hydrogen. The numerical modeling of these flows remain challenging for the transition of small scale instabilities into large scale turbulent structures cannot be modeled by conventional theories. In this work, a model is presented for the simulation of premixed flames with non-unity Lewis number fuels. This model relies on the Levelset/Progress variable approach which was found perfectly suited for the modeling of premixed flames with close to unity Lewis number fuels such as methane. Combined with the solution of an additional transport equation for mixture fraction, this model is formulated and validated in simple 1D laminar premixed flames. The model is found to capture accurately global quantities such as burning velocity and flame thickness as well as mixture fraction fluctuations. Then, this model is applied in Large Eddy Simulation (LES) of a Low Swirl Burner of $\rm H_2$/Air ($\phi=0.4$). The simulation shows the formation of a strongly wrinkled flame with local extinction. The results obtained with this new formulation show significant improvement when compared with experimental measurements. [Preview Abstract] |
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