Setting Simulation Conditions and Controls

In this section, you set the initial conditions, boundary conditions, solver settings, and stopping criteria.

Set the initial conditions for the start of the calculation: temperature, species mass fraction, the turbulence specification method, and the axial velocity of the gas.

Expand the Continua > Physics 1 > Initial Conditions node and set the following properties:


Node	Property	Setting
Species Mass Fraction	Value	O2, 0.233
Species Mass Fraction	Value	N2, 0.767
Static Temperature	Value	293K
Turbulence Specification	Method	K + Epsilon
Turbulent Dissipation Rate	Value	50000 m²/s³
Turbulent Kinetic Energy	Value	30 J/kg
Velocity	Value	[0.9, 0.0] m/s

Set the boundary conditions for the inlets, outer boundary, and outlet boundary. For the outer and outlet boundaries, you set the backflow conditions to the extrapolation method, which extrapolates the flow direction from the interior of the domain. This case requires extrapolation because the flow is not necessarily normal to the boundary.

Expand the Regions > fluid > Boundaries node.

Edit the inlet-1 > Physics Values node and set the following properties:


Node	Property	Setting
Species Mass Fraction	Value	CH4, 0.1563
		O2, 0.1965
		N2, 0.6472
Static Temperature	Value	293 K
Turbulence Intensity	Value	0.1
Turbulent Viscosity Ratio	Value	100
Velocity Magnitude	Value	49.6 m/s

Edit the inlet-2 > Physics Values node and set the following properties:


Node	Property	Setting
Species Mass Fraction	Value	H2O, 0.095
		CO2, 0.117
		O2, 0.054
		N2, 0.734
Static Temperature	Value	1880 K
Turbulence Intensity	Value	0.1
Turbulent Viscosity Ratio	Value	100
Velocity Magnitude	Value	11.4 m/s

Edit the inlet-3 > Physics Values node and set the following properties:


Node	Property	Setting
Species Mass Fraction	Value	O2, 0.233
Species Mass Fraction	Value	N2, 0.767
Static Temperature	Value	293 K
Turbulence Intensity	Value	0.1
Turbulent Viscosity Ratio	Value	100
Velocity Magnitude	Value	0.9 m/s

Select the outer > Physics Conditions > Backflow Specification node and set Direction to Extrapolated.

Edit the outer > Physics Values node and set the following properties:


Node	Property	Setting
Species Mass Fraction	Value	O2, 0.233
Species Mass Fraction	Value	N2, 0.767
Static Temperature	Value	293 K

Right-click the outer node, select Copy, then right-click the outlet node and select Paste.
This action copies the settings from the outer node to the outlet node.

The default under-relaxation factors for the flow, species, energy, and turbulence equations are suitable. To ensure that the two solutions remain synchronized, it is important that the under-relaxation factors for the species and energy equations are the same.

Select the Stopping Criteria > Maximum Steps node and set Maximum Steps to 2200.
This value is sufficient to achieve a steady-state solution.
Save the simulation.