Partially Premixed Combustion Composition PDF Transport

Description

Partially Premixed Combustion and Composition PDF Transport, ANSYS Fluent CFD Training

The present problem simulates combustion in a combustion chamber by ANSYS Fluent software. In the present case, it is assumed that there are three different inlet boundaries, one for pure air, another for a mixture of fuel and air, and the other one for the pilot, where the combusted flow enters to provide the activation energy for the main combustion.

The geometry of the present model is two-dimensional and has been designed using Design Modeler software. We do the meshing of the present model with ANSYS Meshing software. The mesh type is Structured, and the element number is 2352.

This CFD project is the 9th episode of the Combustion Training Course.

Combustion Methodology

The present project is composed of three different phases. In the first stage, a Partially Premixed Combustion model has used to obtain an initial solution of the flow and combustion. Non-Adiabatic energy treatment, along with a Chemical Equilibrium model, is used to model the combustion process.

A PDF table is generated to store data related to changes in temperature, the density of the mixture, and different chemical species mass fractions prior to simulation to be used during the main calculations. Also, the Zimont model has been used for the turbulent flame speed model.

In the second phase, the Composition PDF Transport is enabled to continue the simulation. A Chemkin Mechanism in which detailed reactions and multiple chemical species exist is added to Fluent.

ISAT table, along with Chemistry agglomeration, is used to tabulate the detailed kinetics and reduce the high computational cost regarding the modeling of the detailed chemistry. Using chemistry agglomeration will increase the simulation speed but comes with the penalty of increased error.

Finally, when the second stage of simulation is finished, the chemistry agglomeration model is disabled. Meanwhile, the ISAT table, filled in the second stage, continues to be used to obtain the final accurate solution.

Also, the Energy equation is On to calculate the changes in temperature due to the combustion process, and the Viscous is set as the Standard k-epsilon model.

Combustion Conclusion

After the simulation process was finished, contours such as temperature, velocity, different species’ mass fractions, and streamlines were obtained. As shown in the temperature contour, the temperature has clearly increased in the chamber, indicating that the combustion has taken place.