3 results
Numerical simulations of asymmetric mixing in planar shear flows
- F. F. Grinstein, E. S. Oran, J. P. Boris
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- Journal:
- Journal of Fluid Mechanics / Volume 165 / April 1986
- Published online by Cambridge University Press:
- 21 April 2006, pp. 201-220
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Numerical simulations were performed of the evolution of the Kelvin–Helmholtz instability in planar, free shear layers, resulting from coflow past a splitter plate. The calculations solved the time-dependent inviscid compressible conservation equations. New algorithms were developed and tested for inflow and outflow boundary conditions. Since no turbulence subgrid modelling was included, only the large-scale features of the flow are described. The transition from laminar flow was triggered by transverse pressure gradients and subsequent vorticity fluctuations at the shear layer, near the tip of the splitter plate. The calculations were performed for a range of free-stream velocity ratios and sizes of the chamber enclosing the system. The simulations showed that the resulting mixing layers have more of the faster fluid than the slower fluid entrained in the roll-ups. This effect is in general agreement with the results of recent splitter-plate experiments of Koochesfahani, Dimotakis & Broadwell (1983). The calculated mixing asymmetry is more apparent when the velocity ratio of the two streams is larger, and does not depend significantly on the separation between the walls of the chamber.
14 - Numerical simulations of Type Ia supernovae: deflagrations and detonations
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- By V. N. Gamezo, Laboratory for Computational Physics and Fluid Dynamics, Naval Research Laboratory, Washington, D. C. 20375, USA, E. S. Oran, Laboratory for Computational Physics and Fluid Dynamics, Naval Research Laboratory, Washington, D. C. 20375, USA, A. M. Khokhlov, Laboratory for Computational Physics and Fluid Dynamics, Naval Research Laboratory, Washington, D. C. 20375, USA
- Edited by Peter Höflich, University of Texas, Austin, Pawan Kumar, University of Texas, Austin, J. Craig Wheeler, University of Texas, Austin
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- Book:
- Cosmic Explosions in Three Dimensions
- Published online:
- 11 August 2009
- Print publication:
- 16 December 2004, pp 121-131
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Summary
Abstract
We study a thermonuclear explosion of a carbon-oxygen white dwarf (WD) using a three-dimensional hydrodynamic model with a simplified mechanism for nuclear reactions and energy release. The explosion begins as a deflagration with the flame front highly distorted by the Rayleigh-Taylor instability. Turbulent combustion and convective flows produce an inhomogeneous mixture of burned and unburned materials that extends from the center to about 0.8 of the radius of the expanding WD. At this stage, a detonation is ignited and propagates through the layers of unburned material with the velocity about 12,000 km/s, which is comparable to the expansion velocities induced in outer layers of the WD by the subsonic burning. During the period of detonation propagation, the density of the expanding unreacted material ahead of the shock can decrease by an order of magnitude compared to its value before the detonation started. Because the detonation burns material to different products at different densities, it can create a large-scale asymmetry in composition if it starts far from the WD center. In contrast to the 3-D deflagration model, the 3-D delayed-detonation model of SN Ia explosions does not leave carbon, oxygen, and intermediate-mass elements in central parts of a WD. This removes the key disagreement between simulations and observations, and confirms that the delayed detonation is currently the most promising mechanism for SN Ia explosions.
Introduction
Type Ia supernovae (SNe Ia) [1–10] result from the most powerful thermonuclear explosions in the Universe.
12 - Terrestrial combustion: feedback to the stars
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- By E. S. Oran, Laboratory for Computational Physics and Fluid Dynamics U.S. Naval Research Laboratory Washington, DC 20375 USA
- Edited by Peter Höflich, University of Texas, Austin, Pawan Kumar, University of Texas, Austin, J. Craig Wheeler, University of Texas, Austin
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- Book:
- Cosmic Explosions in Three Dimensions
- Published online:
- 11 August 2009
- Print publication:
- 16 December 2004, pp 100-109
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Summary
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This paper describes how we have used numerical simulations and laboratory combustion experiments to learn about Type Ia thermonuclear supernova explosions. We discuss detonations, deflagrations, and the transition from deflagrations to detonations, and how these relate to exploding white dwarf stars.
Introduction
This paper is for Craig Wheeler (aka Professor J. Craig Wheeler, Captain, ISS Bunbry, often stationed in the Virgo Cluster), who has been a good friend and fellow traveler for many years. Craig is wonderfully enthusiastic, persistently curious, and always asking those painfully “simple” questions for which we have no answers. He has motivated and driven research programs that have brought combustion science to astrophysics.
A cursory study of the multivolume Proceedings of the Combustion Institute shows that combustion can now be loosely defined as the result of fluid dynamics combined with exothermic reactions, and everything this implies. The definition has expanded with the understanding of the controlling phenomena and the range of applications. In the early 1900's, there was combustion and detonation, and the concepts seemed separated. Combustion was defined as oxidation with energy release, with an emphasis on specific chemical reactions. Detonation studies emphasized the fluid dynamics with shocks and explosions. Now these fields have merged and expanded. We now consider exothermic reactions, including the physics, chemistry, structure and dynamics of flames and detonations, including the production products such as pollutants, soot, diamonds, fullerenes, microparticles, and nanoparticles.
The purpose of this paper is to introduce some aspects of combustion and the combustion community to astrophysicists.