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Partially Premixed Combustion

Created using ANSYS 14.5

Problem Specification

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:

  1. 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). 
  2. 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. 
  3. Analyze the results of the system

combustion model uses a modeling approach that solves transport
equations for one or two conserved scalars and the mixture fractions. Multiple chemical
species, including radicals and intermediate species, may be included in the problem
denition. Their concentrations will be derived from the predicted mixture fraction
distribution.
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, 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

Unknown macro: {latex}

$$

Unknown macro: {Ka}

= { (\nu \epsilon)^

Unknown macro: {1/4}

\over (U_

Unknown macro: {laminar flame speed}

)^2}
$$


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