Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Early Stages of Flame Propagation in Tubes with No-slip Walls and the
  Mechanism of Tulip Flame Formation   The early stages of flames propagation in tubes with no-slip walls and the
inversion of the flame front from a convex shape directed towards unburned gas
to a concave shape with a cusp directed to the burned gas, known as a tulip
flame, was investigated for closed and half-open tubes by solving the fully
compressible reactive Navier-Stokes equations with a one-step Arrhenius
chemical model for the highly reactive hydrogen/air and slowly reacting
methane/air mixtures. The development of the tulip flame in hydrogen/air
obtained in simulations with a one-step Arrhenius model was compared with
simulations using a detailed chemical model. It is shown that the inversion of
the flame front and the onset of the tulip flame occurs due to rarefaction
waves generated by the decelerating flame when its surface was reduced due to
extinguishing of the rear parts of the flame skirt at the sidewalls. The
rarefaction waves reduce the flow velocity ahead of the flame, creating an
uneven velocity profile, which facilitate the flame front inversion. In the
case of a flame propagating in a tube with both ends closed, the compression
wave reflected from the tube end opposite to the ignition end, also contribute
to the inversion of the flame front. In the case of fast flames and a
relatively short tube with both closed ends, the rarefaction waves may invert
the flow velocities in the unburned gas towards the propagating flame. The
tulip flame formation mechanism is a purely gas-dynamic phenomenon not
associated with flame instabilities or vortex motion, in agreement with the
conclusion obtained in recent experimental studies [1].

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The categories of this paper are: dg-ga
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The categories of this paper are: astro-ph
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The categories of this paper are: math-ph
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The categories of this paper are: atom-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: quant-ph
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The categories of this paper are: hep-ex
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The categories of this paper are: nucl-ex
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The categories of this paper are: chem-ph
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The categories of this paper are: adap-org
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The categories of this paper are: cs
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The categories of this paper are: cond-mat
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The categories of this paper are: supr-con
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The categories of this paper are: comp-gas
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The categories of this paper are: bayes-an
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The categories of this paper are: q-alg