Step 6: Boundary Conditions

Boundary Conditions

  For the multiphase mixture model, you will specify conditions for the mixture (i.e., conditions that apply to all phases) and the conditions that are specific to the primary and secondary phases. In this tutorial, boundary conditions are required only for the mixture and secondary phase of two boundaries: the pressure inlet (consisting of two boundary zones) and the pressure outlet. The pressure outlet is the downstream boundary, opposite the pressure inlets.

1.   Set the boundary conditions at inlet_1 for the mixture.

Boundary Conditions inlet_1 Edit...

(a)   Enter 500000 ${\rm Pa}$ for Gauge Total Pressure.

(b)   Enter 449000 ${\rm Pa}$ for Supersonic/Initial Gauge Pressure.

  If you choose to initialize the solution based on the pressure-inlet conditions, the Supersonic/Initial Gauge Pressure will be used in conjunction with the specified stagnation pressure (the Gauge Total Pressure) to compute initial values according to the isentropic relations (for compressible flow) or Bernoulli's equation (for incompressible flow). Otherwise, in an incompressible flow calculation the Supersonic/Initial Gauge Pressure input will be ignored by ANSYS FLUENT. In this problem the velocity will be initialized based on the difference between these two values.

(c)   Retain the default selection of Normal to Boundary from the Direction Specification Method drop-down list.

(d)   Retain the default selection of K and Epsilon from the Specification Method drop-down list in the Turbulence group box.

(e)   Enter 0.02 ${\rm m^2/s^2}$ for Turbulent Kinetic Energy.

(f)   Retain the value of 1 ${\rm m^2/s^3}$ for Turbulent Dissipation Rate.

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

2.   Set the boundary conditions at inlet-1 for the secondary phase.

Boundary Conditions inlet_1

(a)   Select vapor from the Phase drop-down list.

(b)   Click Edit... to open the Pressure Inlet dialog box.

i.   Click the Multiphase tab and retain the default value of 0 for Volume Fraction.

ii.   Click OK to close the Pressure Inlet dialog box.

3.   Copy the boundary conditions defined for the first pressure inlet zone ( inlet_1) to the second pressure inlet zone ( inlet_2).

Boundary Conditions inlet_1

(a)   Select mixture from the Phase drop-down list.

(b)   Click Copy... to open the Copy Conditions dialog box.

i.   Select inlet_1 from the From Boundary Zone selection list.

ii.   Select inlet_2 from the To Boundary Zones selection list.

iii.   Click Copy.

  A Warning dialog box will open, asking if you want to copy inlet_1 boundary conditions to inlet_2. Click OK.

iv.   Close the Copy Conditions dialog box.

4.   Set the boundary conditions at outlet for the mixture.

Boundary Conditions outlet Edit...

(a)   Enter 95000 ${\rm Pa}$ for Gauge Pressure.

(b)   Retain the default selection of K and Epsilon from the Specification Method drop-down list in the Turbulence group box.

(c)   Enter 0.02 ${\rm m^2/s^2}$ for Backflow Turbulent Kinetic Energy.

(d)   Retain the value of 1 ${\rm m^2/s^3}$ for Backflow Turbulent Dissipation Rate.

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

5.   Set the boundary conditions at outlet for the secondary phase.

Boundary Conditions outlet

(a)   Select vapor from the Phase drop-down list.

(b)   Click Edit... to open the Pressure Outlet dialog box.

i.   Click the Multiphase tab and retain the default value of 0 for Volume Fraction.

ii.   Click OK to close the Pressure Outlet dialog box.