Turbulent incompressible flow: Cyclone separator


The content of this tutorial is not up to date with the current live version of SimScale. The tutorial setup and the results are still valid! Please do not get confused if styles like buttons and entity names have changed in the meantime.

In this tutorial, a fluid dynamics analysis of a cyclone separator is presented. The flow through the separator is modeled as a incompressible, turbulent flow using a k-epsilon turbulence model. This tutorial is based on the library project Cyclone separator flow which you can find in the public project library of the SimScale platform.

Tutorial Link:

Import tutorial case into workspace


1) Import tutorial project

  • To start this tutorial, you have to import the tutorial project into your ‘Dashboard’ via the link above.
  • Once the ‘Work bench’ is open you will be in the ‘Mesh creator’ tab.
  • The Mesh Creator tab is the place where you can upload CAD models and create meshes for them.
  • The geometry is already available under the ‘geometry’ tree item.
  • Click on the CAD model named “cyclone” to load the CAD model in the viewer.
  • After a few moments, the CAD model is displayed in the viewer like shown in the figure below
  • You can interact with the CAD model as in a normal desktop application

The CAD model displayed in the viewer

2) Create a mesh

In this section we will see how to create a mesh in a very efficient way:

  • To mesh the geometry, click on geometry in the Navigator tree and click on the blue Mesh geometry button in the settings panel.
  • Under Meshes, the new mesh appears as a new tree item
  • Select the “Hex-dominant automatic (only CFD)” operation.
  • This operation creates a hex dominant mesh for fluid flow analysis of internal flow with the option of a refined boundary layer.
  • Select the parameters as shown.

Adding a mesh operation (Hex-dominant automatic (only CFD)) within the Mesh Creator

  • To specify where the refined boundary layer shall be generated, we first have to select all the physical walls of the CAD model
  • Since there are many, we will use the ‘invert selection’ button
  • Therefore choose all inlets and outlets (3 in total) of the model which are NOT physical walls ( 1 inlet and 2 outlets, top and bottom )
  • Then click the ‘Invert selection’ button under the ‘Selection’ option on top of the 3D viewer

Select the inlets and outlets and click on the ‘invert selection’ option


Then all physical walls are selected

  • Now these walls can be assigned to the mesh operation under Surfaces with layers with the Add selection from viewer button.
  • All faces automatically appear under assigned entities and will be used to create the refined boundary layer

Assigning the physical walls from the viewer to the mesh operation

  • Then the mesh operation can be started by the ‘Start’ button on top.

The mesh after its successful computation

3) Simulation setup

To setup the simulation switch to the Simulation Designer tab and create a new simulation.

  • First, we choose the analysis type. First switch to the Fluid Dynamics section of the analysis types
  • Here we will use the Incompressible analysis type, with steady-state and a k-epsilon turbulence model
  • As soon as we save the analysis type choice, the tree is automatically expanded with all the parameters and settings that are necessary to completely specify such an analysis.
  • Therefore you can simply go through the tree to complete the setup
  • All parts that are completed are highlighted with a green check. Parts that do need specification have a red circle
  • Next item is Domain. Choose here the mesh that we just created (via its name)

Assign the mesh to this analysis

  • Next item is Materials. Follow the figures below to Add a new material from the library and the assign it to the volume domain.
  • Next item is Initial conditions. Here you can specify the state of the fluid at the beginning of the simulation. We are using the following:
Variable Value Unit
pressure 0 m^2/s^2
velocity (x, y, z) (0, 0, 0) m/s
k 0.08 m^2/s^2
epsilon 0.036 m^2/s^3
  • The next item Boundary conditions.
  • Add a new boundary condition for Inlet with the following settings and assign the respective face.
  • Add a new boundary condition for Outlet with the following settings and assign the respective faces (top and bottom outlet faces).
  • Add a new boundary condition for Walls with the following settings and select all walls using ‘invert selection’ method.
  • The next item is Numerics. Here one can specify the numerical setup of the simulation.
  • We only change the pressure solver to GAMG and keep the rest as default.
  • 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”
  • Set the parameters as shown in figure below.

Specifying the global parameters of the simulation run

  • The last thing to do for running this simulation is to create a run for it. This means that we take a snapshot of the simulation setup that can not be changed anymore afterwards. This allows us at a later point to always review what kind of setup this simulation run had
  • Click on Create new run
  • The new run is created and you can review all setting by expanding it
  • Then, hit the Start button and confirm
  • We can always see the current status of the run via the progress bar

Convergence plots

4) Post-Processing

  • 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)
  • Follow the figures below for post processing on online platform.

Post-processing via the integrated environment


Clipping the domain


Visualizing the velocity field


Local post-processing - in ParaView