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DNS Studies of Burning Fronts in
Passive-Reactive Diffusion
N.Vladimirova, F.Cattaneo, A.Malagoli, A.Oberman, R.Rosner, O.Ruchayskiy
|
low convection (1.3M mpeg movie) |
high convection (1.2M mpeg movie) |
We study the role of diffusion, heat conduction and turbulent convection in flame acceleration. We consider a simple model for premixed flames. The passive scalars, temperature and concentrations, are advected by a prescribed mean zero divergence-free velocity field, diffuses and reacts according to a nonlinear reaction,
When thermal and material diffusivity are equal (Le=1), the system above reduces to a single equation. In this case, linear g(T)=T corresponds to KPP type reaction. Another common model for reaction is Arrhenius ignition.
Problem 1: Burning in Shear Flow
The reaction term is KPP, and Lewis Number Le = 1.
Problem 2: Burning in Cellular Flow
The flame is propagating in a cellular flow. Depending on the
ratio of cell size (flow length scale) to flame thickness, geometric
optics and diffusive regimes can be observed. Flame acceleration in
the geometrical optics regime is a function of flow velocity only,
while in diffusive regime it also depends on cell size.
The reaction term is KPP, and Lewis Number Le = 1.
Problem 3: Quenching by Shear Flow
The initial band of hot material is distorted by sinusoidal shear.
Reaction term is step function of temperature, so that no burning occur
if temperature is lower than critical. For temperatures higher than
critical burning rate is constant and chosen to make laminar speed
equal to unity.
Problem 4: Quenching by Cellular Flow
The initial band of hot material is distorted by cellular shear.
Reaction term is step function of temperature, so that no burning occur
if temperature is lower than critical. For temperatures higher than
critical burning rate is constant and chosen to make laminar speed
equal to unity.
Problem 5: Quenching at Le > 1
(very preliminary results)
