Setting Up Boundary Conditions

You specify the inflow of gas through the inlet boundary as a parabolic velocity profile as given by Eqn. (5243). The velocity profile is formulated in terms of two parameters: the step height H = 1 m and the maximum velocity V max = 1 m / s .

You set the turbulent length scale at the inlet to 5% of the inlet width. To facilitate correct adaption when changing the step height, the turbulent length scale is parameterized as:
I = 0.05 * 4 * H
(5244)
To set up the boundary conditions:
  1. Create a parameter to define the value of the maximum velocity:
    1. Right-click the Automation > Parameters node and select New > Scalar.
    2. Rename the new scalar parameter to Vmax.
    3. Edit the Vmax node and set the following properties:
      Property Value
      Value 1.0
      Dimensions > Velocity 1
  2. Create a field function to define the parabolic velocity profile:
    1. Right-click the Automation > Field Functions node and select New > Scalar.
    2. Rename the new node to Parabolic Profile.
    3. Edit the Field Functions > Parabolic Profile node and set the following properties:
      Property Setting
      Function Name parabolicProfile
      Dimensions Velocity 1
      Definition
      ${Vmax}*($${Position}[1]-${StepHeight})*(5*${StepHeight}-$${Position}[1])/(${StepHeight}*${StepHeight})/4
  3. Define the inlet boundary using a parabolic velocity profile:
    1. Edit the Regions > Backward Facing Step > Boundaries > Inlet > Physics Conditions > Turbulence Specification node and set the Method to Intensity + Length Scale.
    2. Edit the Inlet > Physics Values > Turbulent Length Scale node and set Value to 0.05*${StepHeight}*4.
    3. Edit the Inlet > Physics Values > Velocity Magnitude node and set the following properties:
      Property Setting
      Method Field Function
      Scalar Function Parabolic Profile
  4. Set the heat flux on the bottom wall:
    1. Edit the Boundaries > Step Bottom > Physics Conditions > Thermal Specification node and set Condition to Heat Flux.
    2. Edit the Physics Values > Heat Flux node and set Value to 500 W/m^2
  5. Save the simulation.