Setting up the Fan Interfaces

Two fans drive the flow inside the PC case.

In this tutorial, you model the case fans using fan interfaces. A fan interface models the pressure rise through an axial fan as a function of local flow rates or velocity. A fan interface can only be used between regions that belong to the same fluid continuum. In this tutorial, the fan interfaces are located between Air Case and Air Inlet and between Air Case and Air Outlet.

Using parts-based interfaces and per-contact values, you can model multiple fans using a single interface. In this tutorial, you model two identical fans, each defined by a part contact, using a single interface.

When you set up a fan interface, you supply the fan performance curve that corresponds to the physical fan that you are modeling. The fan performance curve specifies the pressure drop across the fan interface as a function of volumetric flow rate. The performance curve for the fans that are used in this tutorial is shown below. This data corresponds to the fan running at 800 rpm. In this tutorial, you run the fan at 1200 rpm—Simcenter STAR-CCM+ scales the curve using fan laws.

The polynomials that define the fan performance curve are:

y=5.3−494.0x
y=5.05−318.0x
y=4.1−30.3x
y=6.5−394.0x
y=11.7−918.0x

Set up the fan interface:

  1. Expand the Interfaces node.
  2. Select the Case Fans node and set Type to Fan Interface.
  3. Set Allow Per-Contact Values to True.
    The Contact Subgroupings node is added to the Case Fans node.
  4. Expand the Case Fans > Contact Subgroupings > Subgrouping 1 node.
    The Subgroup 1 node contains the contacts for the inlet fan and outlet fan.
  5. Rename Subgroup 1 to Inlet Fan.
  6. Right-click the Subgrouping 1 node and select New.
    A new subgroup, Subgroup 1, is added to Subgrouping 1.
  7. Rename Subgroup 1 to Outlet Fan.
  8. Select Outlet Fan and set Objects to Air Outlet/Air Case > Outlet Downstream/Outlet Upstream.
Make sure that the orientation of each fan is correct. The flow moves from the upstream side of the interface to the downstream side of the interface:
  1. Select the Case Fans > Orientation node and set Mode to Manual.
  2. Right-click Orientation and select, Reverse Contacts.
  3. In the Reverse Contacts dialog, expand the contacts folders.
    Each contact has an icon with a direction arrow, , to indicate the orientation of the interface. For Inlet Upstream/Inlet Downstream, the arrow indicates that the flow is moving from the upstream side of the interface to the downstream side of the interface, which is correct. For the Outlet Downstream/Outlet Upstream contact, arrow indicates that the flow is moving from the downstream side of the interface to the upstream side of the interface, which is incorrect.
  4. To correct the orientation of the outlet fan interface, select the Air Outlet/Air Case > Outlet Downstream/Outlet Upstream node and click OK.
  5. Select the Case Fans > Physics Conditions > Fan Curve Type node and set Curve Type to Polynomial.
  6. Expand the Case Fans > Physics Values node.
  7. Select the Fan Curve Polynomial node and set Specify by Part Subgroup to True.
    The By Contact Subgroup node appears within the Fan Curve Polynomial node.
Define the fan curve for the inlet fan:
  1. Expand the Fan Curve Polynomial > By Contact Subgroup > Inlet Fan node.
  2. Select the Fan Curve Polynomial node and click next to the Polynomial property.
  3. In the Fan Curve Polynomial dialog:
    1. Set Number of Intervals to 5.
      This property specifies the number of polynomials that define the fan curve.
    2. Set Interval Ranges to [0.0, 0.00142, 0.0033, 0.00661, 0.00991, 0.0127].
      This property defines the upper and lower value for the volumetric flow rate for each interval. For example, the first interval has a lower value of 0.0 m^3/s and an upper value of 0.00142 m^3/s.
    3. Set Number of Coefficients to [2, 2, 2, 2, 2].
      This property specifies how many coefficients each polynomial contains. In this tutorial, each polynomial consists of 2 coefficients. The number of coefficients in each range sets the number of exponents.
    4. Set Coefficients to [5.3, -494.0, 5.05, -318.0, 4.1, -30.3, 6.5, -394.0, 11.7, -918.0].
      This property specifies the values of the coefficients for each of the polynomials.
    5. Click OK to close the Fan Curve Polynomial dialog.
The Data Rotation Rate property specifies the speed at which the fan data was collected, in this case 800 rpm. The Operating Rotation Rate property specifies the speed at which you want the fan to run — in this case 1200 rpm.
  1. Set the Operating Rotation Rate to 1200.0 rpm.
  2. Set the Data Rotation Rate to 800.0 rpm.
The inlet and outlet fan are the same. Copy the fan data from the inlet fan to the outlet fan:
  1. Right-click the Inlet Fan > Fan Curve Polynomial node and select Copy.
  2. Right-click the Outlet Fan > Fan Curve Polynomial node and select Paste.
To have the correct thermal conductivity on either side of the interfaces, make sure that all remaining interfaces in the simulation are set to contact interfaces:
  1. Multi-select all the interfaces, except for the fan interface, and make sure that Type is set to Contact Interface.
  2. Save the simulation.