function, which is evaluated by the mean and variance of the mixture fraction. The mean state space variables are computed by integrating the instantaneous values, computed by the chemical equilibrium, over the PPDF function.
In this tutorial, a propane combustion problem is simulated using the Presumed Probability Density Function (PPDF) reaction model for unpremixed flames. The problem geometry involves air entering the combustion chamber through three air inlets and propane gas entering through a fuel inlet, as indicated in the introductory Combustion Tutorials section.
The PPDF model assumes that the combustion is mixing-limited and thus represents the state-space variables such as density, temperature and species concentration as a function of mixture fraction and enthalpy. The mixture fraction variable tracks the mixing between the fuel and oxidizer streams. The local subgrid scale mixing between these two streams is represented by a presumed probability density function (PPDF) in the shape of a function, which is evaluated by the mean and variance of the mixture fraction. The mean state space variables are computed by integrating the instantaneous values, computed by the chemical equilibrium, over the PPDF function.
In this tutorial, adiabatic conditions are assumed and as a result enthalpy and the other state space variables can be computed as a function of mixture fraction alone (see the Adiabatic PPDF Equilibrium Model section in the User Guide). For non-adiabatic boundary conditions and/or gas-phase radiation, the Non-Adiabatic PPDF Equilibrium model should be used.