Actuator disks provide a simple way of modeling rotating parts in steady flow simulations. They are applicable to use cases involving helicopters, fans and propellers. For the Piper Cherokee we'll use an actuator disk to model the airplane's propeller.
Note: This project builds on the Piper Cherokee project. If you haven't already, follow the steps in that project, then return here to learn how to add an actuator disk.
Create a Disk
First we need to add and position a new actuator disk:
Click the + symbol to the right of the Geometry section in the Geometry panel.
Select Disk. A new surface entity named Disk 1 will be created in the Surfaces section.
Rename Disk 1 to Propeller.
In the properties panel, set Inner Radius to 0.1. This represents the area around the shaft of the propeller, where there would be no blades.
Set Outer Radius to 1. This represents to outer width of the disk swept by the propeller blades.
Position the disk at a Center of 0.2, 0, 0.
Select the Normal to be defined via a Vector, and set the values -1, 0, 0. The minus value in this example ensures that the thrust of the disk is in the correct direction relative to the direction of movement of the airplane.
You should now see a disk located in roughly the position where the Piper Cherokee's real propeller would be.
Next we must assign a disk model to the disk so that it has an effect on the flow field.
Apply a Disk Model
There are three physical disk models to choose from:
Uniform Thrust: This applies a uniform force across the disk.
Radial Distribution: This allows you to set radially varying profiles for thrust, torque and radial force.
Blade Element Model: This uses tables of airfoil aerodynamic data to model the forces across the disk.
The most simple actuator disk physical model is the uniform thrust model. This applies a constant force on the flow field across the disk surface.
To apply this model to the actuator disk we previously created:
Expand your Fluid Flow physics in the control panel.
Click the + symbol to the right of Physical Models.
Select Disk Model.
In the properties panel ensure Type is set to Uniform Thrust.
If you have previously run and analyzed the Piper Cherokee simulation without a disk, you will have seen that the drag on the airplane was about 850 N. To approximate cruise conditions, set a Disk Thrust of 1,000 N.
Ensure the disk has been selected in the list of disks.
Now that we have created an actuator disk and applied a physical model, we can run a simulation to see the effect of this disk propeller.
Run the Simulation
If everything is set up correctly in the control panel, the Run Simulation button at the top will become active.
Clicking on this button will launch a new simulation and open a new Simulation tab showing you the current status of the run.
Once the simulation has finished, this new tab can also be used to analyze the results and create visualizations.