Step 5: Boundary Conditions

Boundary Conditions

1.   Convert the symmetry zone to the axis type.

Boundary Conditions symmetry-5

  The symmetry zone must be converted to an axis to prevent numerical difficulties where the radius reduces to zero.

(a)   Select axis from the Type drop-down list.

  A Question dialog box will open, asking if it is OK to change the type of symmetry-5 from symmetry to axis. Click Yes to continue.

  The Axis dialog box will open and display the default name for the newly created axis zone. Click OK to continue.

2.   Set the boundary conditions for the air inlet ( velocity-inlet-8).

Boundary Conditions velocity-inlet-8 Edit...

  To determine the zone for the air inlet, display the mesh without the fluid zone to see the boundaries. Use the right mouse button to probe the air inlet. ANSYS FLUENT will report the zone name ( velocity-inlet-8) in the console.

(a)   Enter air-inlet for Zone Name.

  This name is more descriptive for the zone than velocity-inlet-8.

(b)   Enter 0.5  ${\rm m/s}$ for Velocity Magnitude.

(c)   Select Intensity and Hydraulic Diameter from the Specification Method drop-down list in the Turbulence group box.

(d)   Retain the default value of 10 ${\rm\%}$ for Turbulent Intensity.

(e)   Enter 0.44  ${\rm m}$ for Hydraulic Diameter.

(f)   Click the Thermal tab and retain the default value of 300  ${\rm K}$ for Temperature.

(g)   Click the Species tab and enter 0.23 for o2 in the Species Mass Fractions group box.

(h)   Click OK to close the Velocity Inlet dialog box.

3.   Set the boundary conditions for the fuel inlet ( velocity-inlet-6).

Boundary Conditions velocity-inlet-6 Edit...

(a)   Enter fuel-inlet for Zone Name.

  This name is more descriptive for the zone than velocity-inlet-6.

(b)   Enter 80  ${\rm m/s}$ for the Velocity Magnitude.

(c)   Select Intensity and Hydraulic Diameter from the Specification Method drop-down list in the Turbulence group box.

(d)   Retain the default value of 10 ${\rm\%}$ for Turbulent Intensity.

(e)   Enter 0.01  ${\rm m}$ for Hydraulic Diameter.

(f)   Click the Thermal tab and retain the default value of 300  ${\rm K}$ for Temperature.

(g)   Click the Species tab and enter 1 for ch4 in the Species Mass Fractions group box.

(h)   Click OK to close the Velocity Inlet dialog box.

4.   Set the boundary conditions for the exit boundary ( pressure-outlet-9).

Boundary Conditions pressure-outlet-9 Edit...

(a)   Retain the default value of 0  ${\rm Pa}$ for Gauge Pressure.

(b)   Select Intensity and Hydraulic Diameter from the Specification Method drop-down list in the Turbulence group box.

(c)   Retain the default value of 10 ${\rm\%}$ for Backflow Turbulent Intensity.

(d)   Enter 0.45  ${\rm m}$ for Backflow Hydraulic Diameter.

(e)   Click the Thermal tab and retain the default value of 300  ${\rm K}$ for Backflow Total Temperature.

(f)   Click the Species tab and enter 0.23 for o2 in the Species Mass Fractions group box.

(g)   Click OK to close the Pressure Outlet dialog box.

  The Backflow values in the Pressure Outlet dialog box are utilized only when backflow occurs at the pressure outlet. Always assign reasonable values because backflow may occur during intermediate iterations and could affect the solution stability.

5.   Set the boundary conditions for the outer wall ( wall-7).

Boundary Conditions wall-7 Edit...

  Use the mouse-probe method described for the air inlet to determine the zone corresponding to the outer wall.

(a)   Enter outer-wall for Zone Name.

  This name is more descriptive for the zone than wall-7.

(b)   Click the Thermal tab.

i.   Select Temperature in the Thermal Conditions list.

ii.   Retain the default value of 300  ${\rm K}$ for Temperature.

(c)   Click OK to close the Wall dialog box.

6.   Set the boundary conditions for the fuel inlet nozzle ( wall-2).

Boundary Conditions wall-2 Edit...

(a)   Enter nozzle for Zone Name.

  This name is more descriptive for the zone than wall-2.

(b)   Click the Thermal tab.

i.   Retain the default selection of Heat Flux in the Thermal Conditions list.

ii.   Retain the default value of 0  ${\rm W/m}^2$ for Heat Flux, so that the wall is adiabatic.

(c)   Click OK to close the Wall dialog box.