Buckmaster Research

Urbana, IL, United States

Buckmaster Research

Urbana, IL, United States

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Buckmaster J.,Buckmaster Research | Jackson T.L.,University of Illinois at Urbana - Champaign | Jackson T.L.,University of Florida
Combustion Theory and Modelling | Year: 2014

We pose the following question: 'Within the context of the classical shrinking-core model for sub-micron aluminium combustion, allowing only for the diffusion of atomic oxygen (no aluminium diffusion), but with two non-classical ingredients (large Knudsen number heat losses to the ambient atmosphere and a fractal reacting surface), are the solutions consistent with four experimental facts and data sets: (i) burn times; (ii) particle temperatures; (iii) maximum temperatures independent of particle size for small Damköhler numbers; and (iv) also for small Damköhler numbers a burn law of the form d1 - ν-t (where d is the particle diameter and ν ~ 0.7 or so)?' In the analysis we first consider a non-fractal model and scale the lengths with (where is the diffusion coefficient and k is the reaction-rate constant) and time with (where ρ- is the aluminium density and co is a characteristic value of the O density within the alumina). Burn times are calculated which follow a linear d-t law for small values of kL/D(L = D/2), the Damköhler number, and a quadratic d2-t law for large values of. Enhanced temperatures (greater than the ambient) arise for small values of with maximum values that are size independent. Since the small Damköhler d-t law does not agree with experimental data, we introduce a fractal concept into the model, as this can generate a burn law of the observed form. However, we then find that the maximum temperature is not independent of particle size. © 2014 Taylor & Francis.


Zhang J.,University of Illinois at Urbana - Champaign | Zhang J.,Florida Institute of Technology | Jackson T.L.,University of Illinois at Urbana - Champaign | Buckmaster J.D.,Buckmaster Research | Freund J.B.,University of Illinois at Urbana - Champaign
Combustion and Flame | Year: 2012

Determining the hazard classification of energetic materials is important for transportation safety and storage concerns. To avoid costly grain redesign and additional testing, a model that adequately predicts the shock sensitivity of energetic materials is required, particularly the outcome of the Naval Ordnance Laboratory Large Scale Gap Test. The goals of this effort are to develop and validate computational tools that predict the shock sensitivity of energetic materials. Specifically, to use our packing code, Rocpack, to generate morphologies of interest for shock sensitivity assessments, and to use our CFD code, RocSDT, to propagate shocks of various strengths through the pack to predict the onset of detonation.Dealing accurately with the material interfaces in this problem is a long-standing challenge, as familiar strategies lead to spurious temperature spikes, and therefore spurious reaction rate spikes. We describe a new strategy, which does not generate spurious spikes, and demonstrate via a number of test problems that numerical convergence can be achieved. We also examine two problems that are stepping stones to a complete simulation; both are planar. In the first, we consider the passage of a shock wave through pure HMX in which a line of hot spots of the kind generated by void collapse are located a short distance behind the shock. When the hot spot spacing is large, the shock remains a shock; when small, transition to detonation occurs. In the second problem we also insert hot spots, but into a matrix of HMX particles and binder. © 2011 The Combustion Institute.


Zhang J.,University of Illinois at Urbana - Champaign | Jackson T.L.,University of Illinois at Urbana - Champaign | Buckmaster J.,Buckmaster Research | Najjar F.,Lawrence Livermore National Laboratory
Journal of Propulsion and Power | Year: 2011

A computational framework is developed to investigate nozzle erosion in solid-propellant rocket motors. The calculations have several novel features. Among these is an accounting of three-dimensional effects, most strikingly for a vectored nozzle but also in the description of the turbulent flow. Also, instead of the hitherto universal strategy of merely solving the nozzle flow with uniform inlet conditions, strategies by which the chamber flow with its nonuniform efflux can be coupled to the nozzle flow while still resolving the nozzle boundary layer are discussed. The chamber flow is approximated by either full motor simulations, which do not resolve the boundary layer, or by an asymptotic strategy valid for slender chambers: one first used in turbulent boundary-layer studies. The manner in which the chamber efflux conditions are used as nozzle inlet conditions is part of the discussion. The results suggest that specifying turbulent rather than uniform inlet conditions can have a significant effect on nozzle erosion. Copyright © 2011 by the American Institute of Aeronautics and Astronautics, Inc.


Buckmaster J.,Buckmaster Research | Jackson T.L.,University of Illinois at Urbana - Champaign | Jackson T.L.,IllinoisRocstar, LLC
Combustion Theory and Modelling | Year: 2013

We revisit the shrinking-core model of sub-micron aluminum combustion with particular attention to the mass flux balance at the reaction front which necessarily leads to a displacement velocity of the alumina shell surrounding the liquid aluminum. For the planar problem this displacement simply leads to an equal displacement of the entire alumina layer, and therefore a straightforward mathematical framework can be constructed. In this way we are able to construct a single curve which defines the burn time for arbitrary values of the diffusion coefficient of O atoms, the reaction rate, the characteristic length of the combustion field, and the O atom mass concentration within the alumina provided that it is much smaller than the aluminum density. This demonstrates a transition between a 'd2-t' law for fast chemistry and a 'd-t' law for slow chemistry. For the spherical geometry, the one of physical interest, the outward displacement velocity creates not a simple displacement, but a stress field which, when examined within the framework of linear elasticity, strongly suggests the creation of internal cracking. We note that if the molten aluminum is pushed into these cracks by the high internal pressure characteristic of the stress field, its surface, where reaction occurs, could be fractal in nature and affect the fundamental nature of the burning law. Indeed, if this ingredient is added to the planar model, a single curve for the burn time can again be derived, and this describes a transition from a 'd2-t' law to a 'dν-t' law, where 0<ν<1. © 2013 Copyright Taylor and Francis Group, LLC.


Jackson T.L.,University of Illinois at Urbana - Champaign | Hooks D.E.,Los Alamos National Laboratory | Buckmaster J.,Buckmaster Research
Propellants, Explosives, Pyrotechnics | Year: 2011

In this article, we present a strategy for packing realistic crystals, critical for mesoscale simulations, and predictions. The current packing code uses a dynamic algorithm, with crystal shapes represented by level sets, to create appropriate packs of the microstructure for an energetic material. Crystal shapes include the nitramines HMX, RDX, PETN, and CL20. Two series of packs are considered: a bidisperse pack with size ratio 1:0.3 and a polydisperse pack. We also construct equivalent packs of spheres for comparison purposes. Higher-order statistics are computed and compared. We show that the second-order statistics are essentially independent of particle shape when the packing fraction is held constant. The second-order statistics do, however, depend on the polydispersity. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Grant
Agency: Department of Defense | Branch: Air Force | Program: STTR | Phase: Phase II | Award Amount: 750.00K | Year: 2010

Determining the hazard classification of new propellant formulations is important for transportation safety and storage concerns. To avoid costly grain redesign and additional testing, a model that adequately predicts the shock sensitivity, including the outcome of the Naval Ordnance Laboratory Large Scale Gap Test, of modern solid propellants is required. The goals of this proposal are to develop and validate computational tools that predict the shock sensitivity of solid propellant formulations. In particular, we plan to (i) use our packing code, Rocpack, to generate morphologies of interest for shock sensitivity assessments, (ii) modify our CFD code to include appropriate chemistry models, (iii) modify our CFD code to propagate shocks of various strengths through the pack to predict the onset of detonation. In Phase I, we made key steps toward these objectives. We also plan to carry out an experimental program to validate the numerical solvers. BENEFIT: Determining the hazard classification of new propellant and explosive formulations is important for transportation, safety, and storage concerns. To avoid costly grain redesign and additional testing, a model that adequately predicts the shock sensitivity, including the outcome of the Naval Ordnance Laboratory Large Scale Gap Test, of modern solid propellants is required. This information will be of great value to solid rocket manufacturers, to large gun manufacturers, and their customers in the U.S. Department of Defense


Jackson T.L.,University of Florida | Buckmaster J.D.,Buckmaster Research | Zhang J.,Florida Institute of Technology | Anderson M.J.,IllinoisRocstar, LLC
Combustion Theory and Modelling | Year: 2015

We examine a pore in an energetic material whose collapse following the passage of a strong genesis shock wave, the subsequent ignition of reactive gases within it produced by pyrolysis at the pore boundary, and the emission of shock waves as a consequence of this ignition, can lead to a detonation. The interest in such a problem arises from the interest in knowing the sensitivity and therefore the safe-handling protocol of energetic materials. We follow the initial pore collapse, before melting occurs, using rational analytical strategies, but to describe the later stages, with full coupling between the physics in the condensate and those in the pore cavity, we describe a numerical strategy. The results provide a description of the power deposition into the energetic material and lead to a power deposition model for the macro-scale, one that encompasses a number of pores. For suitable parameter choices, shock waves generated by the pores interact to form a detonation upstream of the genesis shock. © 2015, Taylor & Francis.


Buckmaster J.D.,Buckmaster Research
Combustion Theory and Modelling | Year: 2015

We examine the problem of sub-micron aluminium drop combustion when both O diffusion and Al diffusion occur. During the unsteady evolution of the combustion field the oxide that is generated has the form of a shell whose inner surface encloses an aluminium bath and whose outer surface is exposed to an air bath. The diffusing atoms can react at these surface baths and also, in principle, between themselves in the interior of the oxide. However, the mass concentrations of the atoms are small so that the interior collisions necessary for this reaction are negligible.With this important simplification we are able to define a model that leads to an analytical discussion. For small Damköhler numbers (of which there are two, one defined by the O atoms the other by the Al atoms) the relative values of the bath reaction rates determine the proportion of oxide accretion on the outer surface to accretion on the inner surface. For large Damköhler numbers the relative values of the diffusion coefficients play the same role. © 2015 Taylor & Francis.

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