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Pre-Analysis & Start-Up
In this tutorial, you will learn how to set up and solve a turbulent reactive flow - particularly, a partially premixed combustion case, in which there are both premixed and non premixed conditions. You will:
- Use the probability density function (PDF) method to track the mixture fraction and modeling the chemistry in the system (used for non-premixed, mixing combustion cases).
- Learn the appropriate inputs and solver techniques using the turbulent Zimont Flame Speed model to close the turbulent quantities, typically used for premixed combustion cases.
- Analyze the results of the system
The non-premixed combustion model solves transport equations for conserved scalars and mixture fractions. The amounts of chemical species present are derived from the predicted mixture fraction distribution, present in the precomputed PDF tables. These tables are generated by knowing the species that can be present, as well as the inflow conditions and properties of the mixture.
For the premixed combustion component which will be solved at simulation runtime, the Zimont turbulent flame speed model includes the laminar flame speed (which determines the chemistry of the system) and the flame front evolution due to turbulence. The assumption to use this model is that the turbulence lengthscale in the flame is smaller than the flame thickness (Karlovitz number Ka > 1) where
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{include: FLUENT Google Analytics} {include: Partially Premixed Combustion - Panel} h1. Pre-Analysis & Start-Up \\ In this tutorial, you will learn how to set up and solve a turbulent reactive flow - particularly, a partially premixed combustion case, in which there are both premixed and non premixed conditions. You will: # Use the probability density function (PDF) method to track the mixture fraction and modeling the chemistry in the system (used for non-premixed, mixing combustion cases). # Learn the appropriate inputs and solver techniques using the turbulent Zimont Flame Speed model to close the turbulent quantities, typically used for premixed combustion cases. # Analyze the results of the system The non-premixed combustion model solves transport equations for conserved scalars and mixture fractions. The amounts of chemical species present are derived from the predicted mixture fraction distribution, present in the precomputed PDF tables. These tables are generated by knowing the species that can be present, as well as the inflow conditions and properties of the mixture. For the premixed combustion component which will be solved at simulation runtime, the Zimont turbulent flame speed model includes the laminar flame speed (which determines the chemistry of the system) and the flame front evolution due to turbulence. The assumption to use this model is that the turbulence lengthscale in the flame is smaller than the flame thickness (Karlovitz number Ka > 1) where {latex} $$ {Ka} = { (\nu \epsilon)^{1/4} \over (U_{laminar flame speed})^2} $$ {latex} |
Combining
...
these
...
two
...
models
...
is
...
straightforward.
...
The
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reaction
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progress
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variable
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c
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is
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used
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to
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track
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the
...
location
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of
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the
...
flame,
...
called
...
the
...
flame
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front.
...
Before
...
(to
...
the
...
left
...
of)
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the
...
flame
...
front
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at
...
c=0,
...
the
...
mixture
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is
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unburnt,
...
and
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the
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mass
...
fractions
...
and
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other
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variables
...
are
...
computed
...
using
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mixture
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the
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precomputed
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mixture
...
fraction
...
PDFs.
...
Inside
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the
...
flame,
...
a
...
combination
...
of
...
the
...
two
...
models
...
is
...
used.
...
In
...
the
...
burnt
...
area
...
(to
...
the
...
right
...
of
...
the
...
flame
...
at
...
c=1),
...
the
...
equilibrium
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mixture
...
fraction
...
is
...
computed.
...
This
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method
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is
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typically
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limited
...
to
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combustion
...
systems
...
that
...
only
...
contain
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2
...
inflow
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streams.
...
Using
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swirl
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conditions
...
on
...
one
...
of
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the
...
streams
...
is
...
useful
...
as
...
it
...
promotes
...
mixing
...
of
...
the
...
two
...
streams;
...
reducing
...
problems
...
with
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flame
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initialization
...
and
...
extinction.
...
The
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turbulence
...
model
...
that
...
will
...
be
...
used
...
is
...
the
...
2
...
equation
...
k-ε
...
model,
...
described
...
in
...
detail
...
in
...
the
...
Turbulent
...
Jet
...
tutorial
...
pre-analysis.
...
...