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Tutorial: Turbulent Incompressible Flow in a Cyclone Separator

Overview

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.

Visualization of Velocity Inside a Cyclone Separator
Visualization of Velocity Inside a Cyclone Separator

This tutorial provides a step-by-step guide on how to set up an incompressible flow simulation for a cyclone separator.

Create Simulation

As a first step, import the tutorial project into the SimScale workbench.

By importing the tutorial project, a new project will be created for you, and the ‘Workbench’ will open with the prepared tutorial geometry already loaded into the viewer.

Workbench View of Simscale
Workbench View
  • To create a new simulation, click on the “+” button next to ‘Simulations’ in the tree or the “Create Simulation” button on the geometry panel.
Creating a Simulation in SimScale
Creating a Simulation
  • Select the “Incompressible” analysis type and click “Create Simulation“.
Simulation Tree in simscale
Simulation Tree
  • A new simulation tree containing all parameters and settings needed to define the conditions of the analysis will be created.
Simulation Tree and Simulation Model Options in SimScale
Simulation Tree and Simulation Model Options
  • All setup steps that are completed are highlighted with a green check. Steps that require some user input are shown with a red circle. Steps that have a blue circle indicate optional settings.
  • For this tutorial, we will use the “k-omega SST” turbulence model to run a “Steady-state” analysis.

Simulation Setup

Materials

Now it’s time to define the part materials.

  • Click on ‘+‘ on the Fluid sub-tree item under Materials to create a new fluid material.
Starting a Material Assignment in SimScale
Starting a Material Assignment
  • The Material Library opens. Select “Air” and then click “Apply“.
Material List in SimScale
Material List

Initial Conditions

Initial conditions can be used to initialize certain result fields with expected steady-state conditions. If guessed correctly, this will help with faster convergence of the solution. In our case, we’d like to define initial values for some components.

Defining Initial Conditions in Simscale
Initial Conditions
  • Expand the Initial conditions simulation tree item. Then click the (k) Turbulence kinetic energy. The value will be set to \(3.375*10^{-3} m^2/s^2\).
  • Next, the value of the Specific dissipation rate(\(\omega\)) will also be set to 3.375 1/s.

Boundary Conditions

Boundary conditions define the external influences acting on our simulation domain. We need to model the cyclone inlets and the pressure outlets as boundary conditions.

Defining boundary conditions for cyclone separator in SimScale
Boundary Conditions
  • To create a new boundary condition, click on “+” on the Boundary conditions tree node in the simulation tree and select “Velocity inlet“.
List of Boundary Conditions for incompressible flow in SimScale
List of Boundary Conditions
  • A velocity of -1 m/s will be given in the z-direction (\(U_z\)) and it will be assigned for “face100@solid1
Velocity Inlet of cyclone separator for simulation in simscale
Velocity Inlet
  • Next, two pressure outlets will be defined at the bottom and the top of the cyclone separator.
Pressure Outlets for cyclone separator simulation in simscale
Pressure Outlets

Numerics

Based on the type of problem, we can modify some of the numerics for better stability and convergence of the simulation. As this is an advanced user feature and requires some knowledge of the underlying solver technology used, we’ll leave the numerics settings with their default values.

Simulation Control

In the Simulation control settings panel, parameters such as start and end times, time step size, auto time-stepping, and the number of processors that shall be used for computing can be defined. the default values will be used for this simulation.

Mesh Setup

  • Select the mesh option and set the parameters as shown in figure below
  • We use the automatic “Hex-dominant (only CFD)” algorithm and set the fineness to “Fine”
Mesh Settings in SimScale
Mesh Settings

Refinements

  • Next, mesh refinements will be added. This is done by clicking “Refinements” under “Mesh“.
Mesh refinements in simscale
Mesh Refinements
  • Firstly, select the ‘Inflate Boundary Layer’ option from the drop down menu
  • To specify where the refined boundary layer shall be generated, we first need to select all the physical walls of the CAD model
  • Since there are many, use the ‘invert selection’ option. Therefore choose all inlet and outlet faces (3 in total) of the model which are NOT physical walls ( 1 inlet and 2 outlets, top and bottom ).
Selected Faces for Invert Selection
Selected Faces for Invert Selection
  • Then click the ‘Invert selection’ option (by right click), as shown below
Invert Selection Assignment in Simscale
Invert Selection Assignment
  • The faces assigned after inverting the selection can be seen below
Selected Faces for inflated boundary layer mesh refinements
Selected Faces
  • Go back to the ‘Mesh’ option and hit the Generate button to start the mesh operation
  • After some time, the mesh generation will be finished and it can be reviewed via the 3D viewer
  • The resulting mesh is shown below
Mesh of Cyclone Separator in simscale
Mesh of Cyclone Separator

Start Simulation

Now the simulation setup is complete and you’re ready to start your simulation. To begin the simulation, a simulation Run needs to be created. A simulation Run creates a snapshot of the current setup and tries to compute the results based on the snapshot settings.

  • To create a new Run, click “+” next to Simulation Runs. Name your simulation and click on “Start“.
Creating a New Simulation Run in SimScale
Creating a New Simulation Run
  • A dialog box will popup which requests a name for the simulation. After giving the simulation a name, the simulation run can start.
Naming a Simulation Run in simscale
Naming a Simulation Run

Results

Computation of the results can take up to a few hours. You’ll be informed via email once your simulation run is finished. Once finished, you’re ready to analyze the results.

  • When the simulation is finished, click on “Solution fields” down in the simulation run tree (or click “Post-process results” in the run panel) to post-process the simulation results. The integrated online post-processor will open.
How to Open Post-processor in SimScale
How to Open Post-processor
  • Select “Results” and click on the icon next to the result quantity you want to visualize, such as “All Velocity[node]“.
Simulation Result of cyclone separator simulation with simscale
Simulation Result

Congratulations! This concludes this incompressible flow analysis for a cyclone separator tutorial.

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