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Documentation

Drone Simulation Using Rotating Zones

This article provides a step-by-step tutorial for the flow simulation around a drone using rotating zones (the propeller) using the moving reference frame (MRF) modelling technique.

flow visualization drone simulation mrf rotating zone
Figure 01: Flow visualization across the drone rotating propeller.

This tutorial teaches how to:

  • Setup and run an incompressible flow simulation.
  • Assign boundary conditions, material, and other models to the simulation.
  • Mesh the geometry with the SimScale standard meshing algorithm.
  • Set up a moving reference frame (MRF) rotating zone.

The typical SimScale workflow will be followed:

  • Prepare the CAD model for the simulation.
  • Set up the simulation.
  • Set up the mesh.
  • Run the simulation and analyze the results.

1. Prepare the CAD model and Select the Analysis Type

First of all, click the button below. It will copy the tutorial project containing the geometry into your own workbench.

The following picture demonstrates what should be visible after importing the tutorial project:

imported project drone simulation mrf rotating zone
Figure 2: Imported project in the SimScale workbench.

1.1 Required CAD Preparation

You can see that there are two geometries in the imported project. The first one is called Drone Parts and the second one called Drone – Original. The original model shows the drone model with its four propellers:

cad model drone simulation mrf rotating zone
Figure 3: Model of the drone to be analyzed.

An important optimization in the simulation is achieved by noticing that this model has two planes of symmetry. This means that we can get away with modelling only one-quarter of the geometry. This is performed in the creation of the bounding box, which covers the desired quarter as shown in the following picture:

symmetry model drone simulation mrf rotating zone
Figure 4: Modeled domain, symmetry, and cylinder for rotating region.

A crucial aspect of the modelling is the creation of the cylinder for the rotating region. This cylinder should cover (with some margin) the faces that will be included in the rotation model. The one used in our case covers the drone propeller, and can be found by having a closer look at the Drone Parts geometry:

geometry detail drone simulation mrf rotating zone
Figure 5: Detail of the geometrical volumes present in the model.
  1. The flow region (gray), which models the volume filled by fluid. Notice that it has a void representing the space occupied by the drone structure and propellers, and that it uses the symmetry of the model as explained above.
  2. A cylinder covering the propeller (blue). This cylinder will be used to create the region of cells rotating and the MRF concept.

Tip

You can better visualize the internal faces by changing the render mode to translucent surfaces. Do this by using the top bar at the viewer.

Important

In case you want to model your own drone, or any external rotating geometry for that matter, you should always follow the modelling convention outlined in this section: a flow region volume with the removed bodies and a cylinder around the rotating region.

1.2 Create the Topological Entity Sets

Topological entity sets are groups of faces so boundary conditions or other assignements can be done faster.

They can be found at the panel on the right side of the workbench:

topological entity sets drone simulation mrf rotating zone
Figure 6: Topological entity sets.

Two of the needed sets are already provided in the project, but the set for the two symmetry planes is still missing. The picture below shows how to add it:

creating topological entity set drone simulation mrf rotating zone
Figure 7: Creating a topological entity set.
  1. First, select the corresponding two faces from the viewer (notice these are the ones that intersect with the drone).
  2. Click the ‘+’ icon next to Topological Entity Sets in the right panel.

In the pop-up dialog that appears, name the set ‘Symmetry’ and click Create new set.

naming topological entity set drone simulation mrf rotating zone
Figure 8: Name and finish the topological entity set creation.

1.3 Create the Simulation

Now we can start with the simulation setup. Follow the steps presented in the picture below to create a new simulation for our geometry:

create simulation drone simulation mrf rotating zone
Figure 9: Creating a new simulation.
  1. Select the Drone Parts geometry from the left panel.
  2. Click the Create Simulation button of the dialog

The simulation library window appears to select the appropriate simulation type:

simulation library drone simulation mrf rotating zone
Figure 10: SimScale simulation library.

Choose Incompressible and click Create Simulation. A new simulation tree will appear at the left panel and a pop-up with the simulation settings, which we will leave at the default values.

2. Set Up the Simulation

2.1 Material Model

To define and assign a material, click the ‘+’ icon next to Materials. Doing so, the SimScale material library will pop up. Select Air from the materials library and click Apply:

materials library drone simulation mrf rotating zone
Figure 11: SimScale materials library.

The material properties window will appear. Assign the Flow Region volume and accept the selection with the check-mark button.

materials properties drone simulation mrf rotating zone
Figure 12: Material parameters for air and assignment of the flow region.

2.2 Boundary Conditions

Now we will define the boundary conditions. In order to create a boundary condition, follow the steps shown in the picture below:

creating boundary condition drone simulation mrf rotating zone
Figure 13: Creating a boundary condition.
  1. Click the ‘+’ button next to Boundary Conditions.
  2. Select the proper type from the drop-down menu.
  3. Set up the physical parameters and assigned faces in the pop-up dialog (not shown in the picture).

Now apply this process for the following boundary conditions:

a. Drone Surface

For the drone faces, a no-slip wall condition is used.

Create a new boundary condition by following the instructions in figure 11 and select ‘Wall’. Now select the Drone topological entity set to assign it to the boundary condition. You can also rename the boundary condition to ‘Drone’.

Leave all parameters as default, as shown in the picture:

drone faces boundary condition drone simulation mrf rotating zone
Figure 14: Drone faces boundary condition.

b. Symmetry Planes

For the symmetry planes, a Symmetry boundary condition is used.

Create it according to the steps presented in figure 11. Once the setup panel pops up, select the Symmetry entity set that was created before for the assignment.

The setup should look as shown in the picture:

symmetry planes boundary condition drone simulation mrf rotating zone
Figure 15: Symmetry planes boundary conditions.

c. Atmosphere

For the faces open to the atmosphere, a custom boundary condition will be used. Follow the same procedure as before to create a custom boundary condition.

creating a custom atmospheric boundary condition in simscale
Figure 16: Custom inlet-outlet boundary condition for the faces open to atmosphere.
  1. As we do not know if the direction of flow at these faces will be inlet or outlet, it will allow the solver to automatically compute it. Therefore we select ‘pressure inlet-outlet’ for the (U) Velocity setup.
    • Define ‘Total pressure’ for the gauge pressure option and assign 0 Pa, which corresponds to atmospheric pressure.
    • We set the turbulence quantities, Turb. kinetic energy and specific dissipation rate to ‘zero gradient’, so that the solver calculates them.
  2. Now assign the topological set Atmosphere to the boundary condition.
  3. If you want you can also rename the boundary condition to ‘Atmosphere’ to keep an overview.

2.3 Propeller Rotation

To specify the rotating propeller in our model, a moving reference frame (MRF) rotating zone is employed. The following picture shows how to create it:

creating rotating zone drone simulation mrf rotating zone
Figure 17: Creating a MRF rotating zone.
  1. Expand Advanced concepts.
  2. Click the ‘+’ button next to rotating zones.
  3. Select MRF rotating zone from the list.

In the pop-up window, assign the Rotating Zone volume and set up the parameters as shown in the picture:

setup of mrf rotating zone
Figure 18: Creating the MRF rotating zone.

You can read more on the topic of MRF rotating zones at the corresponding documentation page:

2.4 Numerics and Simulation Control

For the numeric solver parameters, there is only one parameter that will be changed: The Number of non-orthogonality correctors. This will allow the solver to achieve a better solution for the tetrahedral mesh created by the SimScale standard mesher algorithm:

numerics parameters drone simulation mrf rotating zone
Figure 19: Numerics setup.
  1. Select Numerics from the tree at the left panel.
  2. Set the Number of non-orthogonal correctors to 4.

The Simulation control parameters are left as default.

3. Mesh

For the mesh setup, all settings are left as default, as we will make use of the SimScale standard mesh algorithm. You do not need to click Generate either, as the mesh will be computed as part of the simulation run:

mesh parameters drone simulation mrf rotating zone
Figure 20: Mesh setup.

Now we need to specify that the rotating zone volume corresponds to a cell zone, and not a different region. In order to create a cell zone, click the ‘+’ button next to Cell zones under Mesh at the left panel, then assign the Rotating Zone volume as shown in the picture:

creating cell zone drone simulation mrf rotating zone
Figure 21: Creating a cell zone for the rotating zone.

4. Start the Rotating Zones Simulation

Now that the simulation setup is complete, a new simulation run can be created to perform the computation. In order to do so, click the ‘+’ button next to Simulation Runs at the left panel. In the pop-up window, give a proper name to the run and click Start:

creating simulation run drone simulation mrf rotating zone
Figure 22: Creating and starting a new simulation run.

This computation takes about 36 minutes to be completed. If you can’t wait to see the results, at the end of the article you will find a link to the completed version of the project.

5. Post-Processing

The following result plots were generated using the SimScale online post-processor, and they display the computed flow field around the drone due to the propeller rotation:

wake plot drone simulation mrf rotating zone
Figure 23: Propeller wake visualization.

This plot shows the airflow velocity magnitude across a cutting plane, and black arrows for flow direction. Here the wake created by the propeller can be appreciated alongside the range of flow speed.

flow streamlines plot drone simulation mrf rotating zone
Figure 24: Airflow streams visualization.

This second plot displays the air flow stream lines. It displays the vorticity and the speed variation.

You can analyze your results with the SimScale post-processor. Have a look at our post-processing guide to learn how to use the post-processor.

Congratulations! You finished the drone with rotating zones tutorial!

Note

If you have questions or suggestions, please reach out either via the forum or contact us directly.

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