The Transition to Turbulence of Rayleigh-Taylor Unstable Flames

Details The Transition to Turbulence of Rayleigh-Taylor Unstable Flames The Transition to Turbulence of Rayleigh-Taylor Unstable Flames

Jan 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21730803h&link_type=abstract

American Astronomical Society, AAS Meeting #217, #308.03; Bulletin of the American Astronomical Society, Vol. 43, 2011

Astronomy and Astrophysics

Astronomy

Scientific paper

Part of the uncertainty surrounding the explosion mechanism of Type 1A supernovae is the extent to which the turbulence created by the flame front can speed the flame up. A premixed flame moving against a sufficiently strong gravitational field becomes deformed and creates vorticity. If gravity is strong enough, this vorticity is shed and deposited behind the flame front. We have completed some two-dimensional direct numerical simulations of this shedding process for various values of the gravitational force. If gravity is weak enough, the flame front remains flat and no vorticity is created. If gravity is slightly stronger, the flame front becomes cusped and creates vorticity; long vortices attach to the flame front and extend behind it. For even larger values of gravity, the far end of these vortices becomes unstable and sheds more vortices. For simulations with increased gravity, the position of the shedding instability moves closer to the flame front. Next, the vortex shedding disturbs the flame front, causing the flame to pulsate. These pulsations lose their left/right symmetry and the period of oscillation doubles. For even higher values of gravity, an additional frequency is introduced into the system as the Rayleigh-Taylor instability begins to dominate over burning. Eventually, the pulsations of the flame become quite complex and the interaction between the flame front and the vortices can't be simply described. We have measured the subsequent wrinkling of the flame front by computing its fractal dimension and the energy spectra behind the flame front. Measurements of the fractal dimension suggest that it saturates, implying that any additional speed up of the flame must be due to large-scale stretching or disruption of the flame front. Our simulations were performed at NERSC which is supported by the Department of Energy.

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