Step 7: Boundary Conditions

Boundary Conditions

1.   Set the boundary conditions for the streamwise flow inlet ( velocity-inlet-1).

Boundary Conditions velocity-inlet-1 Edit...

(a)   Change the Zone Name from velocity-inlet-1 to velocity-inlet-duct.

(b)   Enter 20 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)   Enter 1% and 5 in for the Turbulent Intensity and the Hydraulic Diameter, respectively.

(e)   Click the Thermal tab and enter 450 K for the Temperature.

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

2.   Set the boundary conditions for the first injected stream inlet ( velocity-inlet-5).

Boundary Conditions velocity-inlet-5 Edit...

(a)   Change the Zone Name from velocity-inlet-5 to velocity-inlet-plenum1.

(b)   Enter 0.4559 m/s for the Velocity Magnitude.

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

(d)   Enter 1% for Turbulent Intensity and retain the default setting of 10 for Turbulent Viscosity Ratio.

(e)   Click the Thermal tab and retain the setting of 300 K for Temperature.

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

  In the absence of any identifiable length scale for turbulence, the Intensity and Viscosity Ratio method should be used.

For more information about setting the boundary conditions for turbulence, see this chapter in the separate User's Guide.

3.   Copy the boundary conditions set for the first injected stream inlet.

Boundary Conditions velocity-inlet-plenum1 Copy...

(a)   Select velocity-inlet-plenum1 in the From Boundary Zone selection list.

(b)   Select velocity-inlet-6 in the To Boundary Zones selection list.

(c)   Click Copy.

  A Warning dialog box will open, asking if you want to copy velocity-inlet-plenum1 boundary conditions to (velocity-inlet-6). Click OK.

(d)   Close the Copy Conditions dialog box.

Copying a boundary condition does not create a link from one zone to another. If you want to change the boundary conditions on these zones, you will have to change each one separately.

4.   Set the boundary conditions for the second injected stream inlet ( velocity-inlet-6).

Boundary Conditions velocity-inlet-6 Edit...

(a)   Change the Zone Name from velocity-inlet-6 to velocity-inlet-plenum2.

(b)   Verify that the boundary conditions were copied correctly.

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

5.   Set the boundary conditions for the flow exit ( pressure-outlet-1).

Boundary Conditions pressure-outlet-1 Edit...

(a)   Change the Zone Name from pressure-outlet-1 to pressure-outlet-duct.

(b)   Retain the default setting of 0 Pa for Gauge Pressure.

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

(d)   Enter 1% for Backflow Turbulent Intensity and retain the default setting of 10 for Backflow Turbulent Viscosity Ratio.

(e)   Click the Thermal tab and enter 450 K for Backflow Total Temperature.

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

6.   Retain the default boundary conditions for the plenum and hole walls ( wall-4 and wall-5).

Boundary Conditions wall-4 Edit...

7.   Verify that the symmetry planes are set to the correct type in the Boundary Conditions task page.

Boundary Conditions

(a)   Select symmetry-1 in the Zone list.

(b)   Make sure that symmetry is selected from the Type drop-down list.

(c)   Similarly, verify that the zones symmetry-5, symmetry-7, symmetry-tet1, and symmetry-tet2 are set to the correct type.

8.   Define the zones on the non-conformal boundary as interface zones by changing the Type for wall-1, wall-7, and wall-8 to interface.

  The non-conformal mesh interface contains three boundary zones: wall-1, wall-7, and wall-8. wall-1 is the bottom surface of the duct, wall-7 and wall-8 represent the holes through which the cool air is injected from the plenum (Figure  7.4). These boundaries were defined as walls in the original mesh files ( film_hex.msh and film_tet.msh) and must be redefined as interface boundary types.

(a)   Open the Mesh Display dialog box.

General Display...

i.   Select wall-1, wall-7, and wall-8 from the Surfaces selection list.

  Use the scroll bar to access the surfaces that are not initially visible in the Mesh Display dialog box.

Note:   You may need to deselect all surfaces first by selecting the unshaded icon to the far right of Surfaces.

ii.   Click Display and close the Mesh Display dialog box.

(b)   Display the bottom view.

Graphics and Animations Views...

i.   Select bottom in the Views list and click Apply.

ii.   Close the Views dialog box.

  Zoom in using the middle mouse button. Figure  7.4 shows the mesh for the wall-1 and wall-7 boundaries (i.e., hole-1). Similarly, you can zoom in to see the mesh for the wall-1 and wall-8 boundaries (i.e., hole-2).

Figure 7.4: Mesh for the wall-1 and wall-7 Boundaries

(a)   Select wall-1 in the Zone list and select interface as the new Type.

Boundary Conditions

  A Question dialog box will open, asking if it is OK to change the type of wall-1 from wall to interface. Click Yes in the Question dialog box.

  The Interface dialog box will open and give the default name for the newly created interface zone.

i.   Change the Zone Name to interface-duct.

ii.   Click OK to close the Interface dialog box.

(b)   Similarly, convert wall-7 and wall-8 to interface boundary zones, specifying interface-hole1 and interface-hole2 for Zone Name, respectively.