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How do I Model a Fan Curve in SimScale?

This Knowledge Base article describes the steps to model a fan curve in SimScale.

A fan is a mechanical machine that is used to generate fluid flow. As the amount of flow increases, so does the pressure drop across the system, which affects the performance of the fan. Fan manufacturers provide a fan curve, which describes the relation between static pressure, power requirement, rotational speed, and efficiency values per-flow rate conditions. This information is very important for cooling purposes, which is why we need to model the fan curve when possible.

temperature distribution of the gpu, cpu and casing of an electronics box
Figure 1: Temperature distribution of the GPU, CPU, and casing of an electronics box

Approach

Fan curves are usually assigned as a boundary condition, either at the inlet as an intake fan or outlet surface of a fluid domain as an exhaust fan.

two cooling scenarios for an electronics box where the left side is the first scenario where there is an inlet fan where cool air comes in and the right side is the second scenario where the electronics box is cooled with an exhaust fan
Figure 2: Visualization of two cooling scenarios for an electronics box

1. Intake Fan Condition

1.1 Inlet

An intake fan sucks air from the environment through the inlet into the domain.

  1. Create a custom boundary condition by hitting the ‘+’ button next to Boundary conditions (BC).
  2. Select ‘Custom’.
  3. Define the values according to the following figure:
custom boundary condition used to define an intake fan with the graph icon pointed with a blue arrow to show the step on how to show the table data for the fan curve
Figure 3: Intake fan boundary condition
  • (U) Velocity: ‘Pressure inlet velocity‘. This means that the velocity on the fan BC is dependent on the pressure difference, for example, if you expect the flow to come into the system, not the other way around.
  • (P) Modified pressure: ‘(P<fan>) Fan pressure‘. Using this setting, the user can upload a fan-curve.
  • Flow direction: ‘In‘. This is an intake fan, therefore flow should come into the system.

Now, press the graph icon to access the table view, where you can define the fan curve. You can either fill in the table manually or create a .csv file.

a. Manual Fan Curve Definition

You can directly fill in the table as presented in the following figure:

uploaded csv file that represents the fan curve
Figure 4: Example of a fan curve table. The user needs to input a flow-rate variation with respect to fan pressure.

Once you have specified all the values, press ‘Apply’.

b. Upload a .CSV File Containing the Fan Curve Values

Click ‘Browse files’ to upload the .csv file.

browse files button to show the way to upload a csv file to define a fan curve in simscale
Figure 5: Browse to the .csv file to upload the fan curve data.

The figure below shows how the .csv file should be made:

a screenshot of acsv file representing a fan curve with column a as the flow rate and column b as fan pressure
Figure 6: Input requirements for fan curve in a .csv file. Column A is flow rate and column B is fan pressure.

Make sure to have two columns: One representing the flow rate, and the other one the fan pressure. Assign the flow rate and pressure headers as well as the correct units to the corresponding columns. In the picture above, column A is the flow rate and column B is the fan pressure.

1.2 Outlet

Assign ‘Natural convection inlet/outlet’ boundary condition to all the outlets.

visualization of natural convection inlet/outlet boundary condition applied at three faces of the electronics cooling box
Figure 7: Assignment of the natural convection inlet-outlet BC on the exhaust vents

2. Exhaust Fan Condition

Exhaust fans are placed at outlets. They suck air from the domain and throw it to the environment. This leads to the air flowing from the inlet through the domain to the outlet, which can cool the electronic components.

We also need inlet and outlet boundary conditions for the exhaust fan situation and are presented below:

2.1 Inlet

The inlet is modeled as a naturally convective boundary with the Natural convection inlet/outlet BC (see section 1.2).

2.2 Outlet

Create a custom boundary condition again and define the following settings:

Figure 8: Exhaust fan boundary condition with fan curve uploaded
  1. (U) Velocity: Pressure inlet-outlet velocity. This means that the velocity on the fan BC is dependent on the pressure difference. Depending on the inlet-outlet pressure difference, flow can either come into the system or go out.
  2. Flow direction: Out. This is an exhaust fan, therefore flow should leave through the fan.

The rest of the setup is exactly like presented in section 1.1.

Expected Outcome

The following image shows the flow direction and pressure distribution on a plane cut through the domain for the intake fan situation:

visualization of pressure and air flow with velocity vectors of an electronics cooling box where an intake fan is applied
Figure 9: Pressure contour and velocity vectors on a cutting plane, intake fan. Flow enters the domain from top and leaves from right.

Since the fan blows the fluid into the system (see top), a positive pressure field is generated.

The following image shows the flow direction and pressure distribution on a plane cut through the domain for the exhaust fan situation:

visualization of pressure and air flow with velocity vectors of an electronics cooling box where an exhaust fan is applied
Figure 10: Pressure contour on a cutting plane, exhaust fan. Flow enters the domain from right and leaves from top.

Comparing figures 9 and 10, the flow direction has changed. The flow is being sucked out of the domain and, therefore, a negative pressure field is generated in the domain for the exhaust fan scenario.

temperature distribution at the bottom of the electronics box and particle traces show the cooling behavior of the electronics box
Figure 11: Temperature distribution in the electronics box and airflow visualized with streamlines

Important Information

If none of the above suggestions solved your problem, then please post the issue on our forum or contact us.

Last updated: September 14th, 2020

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