arXiv subjects

J. B. Bell

Publications and source records attributed to J. B. Bell.

38 records · Page 3Linked to original sources

arXiv2004

Direct Numerical Simulations of Type Ia Supernovae Flames II: The Rayleigh-Taylor Instability

A Type Ia supernova explosion likely begins as a nuclear runaway near the center of a carbon-oxygen white dwarf. The outward propagating flame is unstable to the Landau-Darrieus, Rayleigh-Taylor, and Kelvin-Helmholtz instabilities, which serve to accelerate it to a large fraction of the speed of sound. We investigate the Rayleigh-Taylor unstable flame at the transition from the flamelet regime to the distributed-burning regime, around densities of $10^7$ g/cc, through detailed, fully resolved simulations. A low Mach number, adaptive mesh hydrodynamics code is used to achieve the necessary resolution and long time scales. As the density is varied, we see a fundamental change in the character of the burning--at the low end of the density range the Rayleigh-Taylor instability dominates the burning, whereas at the high end the burning suppresses the instability. In all cases, significant acceleration of the flame is observed, limited only by the size of the domain we are able to study. We discuss the implications of these results on the potential for a deflagration to detonation transition.

astro-ph↗

arXiv1999

The Thermal Explosion Revisited

The classical problem of the thermal explosion in a long cylindrical vessel is modified so that only a fraction $\a$ of its wall is ideally thermally conducting while the remaining fraction $1-\a$ is thermally isolated. Partial isolation of the wall naturally reduces the critical radius of the vessel. Most interesting is the case when the structure of the boundary is a periodic one, so that the alternating conductive $\a$ and isolated $1-\a$ parts of the boundary occupy together the segments $2π/N$ ($N$ is the number of segments) of the boundary. A numerical investigation is performed. It is shown that at small $\a$ and large $N$ the critical radius obeys a scaling law with the coefficients depending upon $N$. For large $N$ is obtained that in the central core of the vessel the temperature distribution is axisymmetric. In the boundary layer near the wall having the thickness $\approx 2πr_0/N$ ($r_0$--the radius of the vessel) the temperature distribution varies sharply in the peripheral direction. The temperature distribution in the axisymmetric core at the critical value of the vessel radius is subcritical

math.NA↗