Documentation

Tutorial: Incompressible turbulent airflow around a spoiler

In the following tutorial you find a step-by-step instruction to setup a Incompressible turbulent airflow simulation around a spoiler.

Import tutorial case into workbench

  • To begin this tutorial, copy the original project.
  • Once the ‘Work bench’ is open you will be in the ‘Geometries’ tab.
  • Click on the CAD model named “Spoiler” to load the CAD model in the viewer.
  • You can interact with the CAD model as in a normal desktop application
This is a 3D spoiler model, ready for CFD
3D CAD model of the spoiler

Create a New Simulation

  • To create a new simulation click on the ‘+’ option next to ‘Simulations’
  • Select ‘Incompressible’ and click ‘OK’
  • After clicking ‘OK, a new tree will be automatically generated in the left panel with all the parameters and settings that are necessary to completely specify such an analysis
  • All parts that are completed are highlighted with a green check. Parts that need to be specified have a red circle.
    • The blue circle indicates an optional settings that does not need to be completed
The Analysis window, showing the range of possible analysis types
Choosing an incompressible simulation from the Analysis window
  • k-omega SST is used for turbulence modelling
  • Choose Steady-State as we are not running a study that changes over time
Selecting a steady state simulation
Setting the turbulence model and steady state analysis type

Create a mesh

  • Select the mesh option from the tree
  • Set the mesh operation type to “Hex-dominant parametric (CFD only)”.
  • Click on save (the blue tick button)
Using the manual mesh option
Options for setting up the mesh
  • Under the geometry primitives, we specify the Background Mesh Box dimensions by the values shown in figure below
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Background Mesh Box
  • Next is the ‘Material Point’, that specifies the region to be meshed. Enter the parameters as shown and save.
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Material point
  • Next, we define additional primitives of type ‘Cartesian Box’ that will be used for mesh refinement later on
  • Click on the ‘+’ option next to Geometry Primitives and select the Cartesian box from the drop down menu, as shown in figure
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Creating a new geometry primitive
  • Set the parameters as below and save
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Cartesian box parameters
  • Now we move on to the “Mesh Refinements”.
  • To add a refinement click on the ‘+’ next to the Refinements and select the required refinement from the drop down menu
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Adding a mesh refinement
  • To resolve all edges we add a Feature refinement that will refine the cells close to the edges of the spoiler
  • Select the ‘Feature Refinement’ option from the ‘Refinements’ drop down menu
  • Set the parameters as shown below, and save
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Feature refinement
  • Add a refinement of type “surface refinement” to control the cell size on top of the wing surfaces
  • Setup the values and properties as shown in figure below, and assign to the volume ‘solid_0’
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Surface refinement
  • Add a new refinement of type ‘Region refinement’ and enter the values as shown and save
  • Here, select the ‘Cartesian Box’, created earlier and click save
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Region refinement
  • Next we add a set of finer layer cells on the spoiler surface by selecting ‘Inflate boundary layer’ option from the ‘Refinements’ drop down list shown earlier
  • Set the parameters as shown in figure below
  • Select all the faces of the spoiler, and save
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Inflate boundary layer
  • Now, again click on the mesh option, set the bounding box resolution as shown below
  • start the meshing operation
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Start the meshing operation
  • After some time, the mesh will be finished and we can review it via the 3D viewer
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Reviewing the generated Mesh

Adding Materials

  • Next, add the materials from the ‘Material Library’ . First, we start with clicking on sub-tree “Materials”, click on ‘+’ from the options panel as shown.
  • This pops-up a ‘Material Library’ from which we select “Air” and click on ‘Ok’. This will then load the standard properties for Air.
  • Then, assign the material to the domain and save.
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Adding a new material
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Assigning the material to the domain

Initial Conditions

  • Next item is Initial conditions. Here you can specify the state of the fluid at the beginning of the simulation. Specify the following initial conditions:
Variable Value Unit
pressure 0 m2/s2
velocity (x, y, z) (0, 0, 0) m/s
k 0.24 m2/s2
omega 1.78 1/s

Boundary Conditions

Now, we come to define the boundary conditions.

  • To create a boundary condition, click on the ‘+’ option next to the Boundary conditions and select the required boundary condition from drop down menu, as shown in figure.
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Creating a new boundary condition
  • For the Inlet select the ‘Velocity Inlet’ boundary condition, specify the values shown in the figure below, assign inlet face for this boundary condition and click on save.
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Velocity Inlet boundary condition
  • For the outlet add a pressure outlet boundary condition and specify the settings as shown in figure below, assign the outlet face for this boundary condition and save it.
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Pressure Outlet boundary condition
  • For the Side and top sides, select the Slip type wall boundary condition as shown
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Wall Boundary condition
  • Define the bottom face as a ‘Moving Wall’, with wall velocity of 20m/s, as shown below
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Moving Wall boundary condition
  • Lastly, define the “Spoiler” faces as a ‘No-slip’ Wall
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No-slip wall boundary condition

Numerics

  • The next item is Numerics. Here one can specify the numerical setup of the simulation.
  • Use the settings as shown below
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Numerics-I
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Numerics-II
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Numerics-III

Simulation Control

  • Under Simulation control we can specify the global parameters of the simulation run
  • Since we are running a steady-state analysis, the time steps are only “quasi time steps”
  • So setup the parameters as shown.
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Simulation Control

Start a simulation run

  • The last thing to do for running this simulation is to create a run.
  • The new run is created by clicking on the ‘+’ symbol next to ‘Simulation Runs’
  • Give a name to the run and start the run
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Creating a new simulation run

Convergence Plot

  • The convergence can be monitored simultaneously while the simulation is running by clicking on the ‘Convergence plots’ option under the Run
  • The final convergence plot at the end of this simulation run is shown below

 

Convergence Plot
Convergence Plot

Post-Processing

Once the run is finished, the results can be viewed in the Post-processor.

  • The results can now either be post-processed in the integrated post-processing environment (currently in beta)
  • Or they can be downloaded and post-processed locally (e.g. with ParaView)

Use the integrated post-processing system for result analysis as follows:

  • Select the ‘Solution fields’ under the Run to post process the results
  • Click the ‘+’ next to the ‘Cutting Planes’ to create a new cutting plane
  • Set the scalar to ‘All velocit [node]’ to view the velocity distribution around the spoiler cross section
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Velocity contour around the spoiler

 

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