Evolution of flame surface in buoyant and nonbuoyant
turbulent nonpremixed reactions

Said Elghobashi, University
of California, Irvine

The evolution of the stoichiometric mixture
fraction F_{st} isosurface is investigated using
direct numerical simulations of
turbulent nonpremixed reacting flow
with infinite and finite reaction
rates, with or without buoyancy.
After the initial transient, F_{st}
isosurface area
increases monotonically with time;
the rate of increase for the buoyant case
is an order of magnitude higher than that of the
nonbuoyant case.
For the buoyant case, the
Gaussian curvature of the isosurface indicates
the presence of steep ridge-like topology and
the mean reaction rate per unit surface area
is twice that of the nonbuoyant case. The
flame stretch equation:

(1/dA)
d(dA)/dt
= S_{t} + u_{n} grad.n

shows that, for the buoyancy case, the tangential strain rate S

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Last Modified: November 3, 1997