Mixing Tank


1. Create Case

After opening SimFlow, we will create a new case named mixing_tank

1. Go to New panel
2. Provide name mixing_tank
3. Click Create Case

2. Import Geometry

After creating case Download Geometry: impeller.stl.gz

1. Click Import Geometry
2. Select geometry file impeller.stl.gz
3. Click Open

3. Geometry - Impeller

After importing geometry, it will appear in the 3D window.

1. Click Fit View to zoom the geometry

4. Create Geometry - Shaft

The original impeller geometry consists of only blades. To make the impeller complete we will add a shaft using a primitive geometry.

1. Click Create Cylinder
2. Rename cylinder_1 to shaft
(double click on the geometry name to start rename)

3, 4. Define cylinder origin, length, and radius

Origin [m] 0 0 -0.045

Length [m] 0.5
Radius [m] 0.04

5. Create Geometry - Rotating Zone

We want our impeller to be rotating. We will create a cylindrical zone that will be used to divide the mesh into rotating and stationary part.

1. Click Create Cylinder
2. Rename cylinder_1 to rotating_zone
3, 4. Define cylinder origin, length, and radius

Origin [m] 0 0 -0.105

Length [m] 0.6
Radius [m] 0.3

6. Show Impeller

All parts of the geometry are displayed in the graphics window now. Note that rotating_zone encloses the impeller and shaft. In order to see all geometries, we will decrease the opacity of the rotating_zone.

1. Press Esc to exit edit mode then select rotating_zone if it is not selected
2. Click Display Properties
3. Adjust Opacity to 50%

7. Meshing Properties - Impeller

We will enable meshing for impeller geometry.

1. Go to Hex Meshing panel
2. Select impeller
3. Check Mesh Geometry
4. Set mesh refinement

Refinement Min 1 Max 2

8. Meshing Properties - Rotating Zone

Since our domain will consist of a stationary and a rotating part we need to create a mesh interface between the parts. To do this we will create a baffle using the rotating_zone geometry.

1. Select rotating_zone
2. Check Mesh Geometry
3. Check Create Cell Zone
4. Change Refinement Max level to 1
5. Check Create Baffle

9. Meshing Properties - Shaft

We need to also mesh the shaft geometry.

1. Select shaft
2. Check Mesh Geometry

10. Base Mesh - Geometry

Now we will define the outer bounds of the computational domain.

1. Go to Base tab
2. Select Cylinder as the base mesh type
3. Define cylinder axis, origin, length, and radius

Axis Z
Origin [m] -0.18
Length [m] 0.9
Radius [m] 0.6

11. Base Mesh - Mesh

To have an appropriate mesh density we will use the following divisions and grading of the base mesh.

1, 2. Define radial division, radial grading, axial division, and central division

Radial Division 15
Radial Grading 1.02
Axial Division 30

Central Division 15

12. Base Mesh - View

We can preview the Base Mesh in the graphics window.

13. Base Mesh - Boundaries

Now we need to assign individual names to each side of the base mesh. Since we are modeling a closed tank all our boundaries will be defined as walls.

1. Type boundary names accordingly

First Disk walls
Second Disk walls
Cylinder walls

2. Change type of all boundaries to wall

First Disk wall
Second Disk wall
Cylinder wall

14. Material Point

Material Point tells the meshing algorithm on which side of the geometry the mesh is to be retained. Since we are modelling flow inside the tank we need to place the material point between the tank walls and the propeller.

1. Go to Point tab
2. Specify location inside the mesh

Material Point 0 -0.3 -0.1

15. Meshing

Everything is now set up for meshing.

1. Go to Mesh tab
2. Click Mesh button to start meshing process

16. Mesh

After the meshing process is finished the mesh will appear in the 3D graphics window. The mesh used in this tutorial is created for demonstration purposes only, and its resolution should be considerably finer in real case scenario.

1. Click Fit View to zoom the geometry

17. Merge Boundaries - Impeller and Shaft (I)

In order to simplify the definition of boundary conditions, we will merge the shaft and propeller boundaries into a single boundary.

1. Hold Ctrl key and select impeller and shaft boundaries
2. On the impeller boundary select Options
3. Choose Merge operation from the dropdown menu

18. Merge Boundaries - Impeller and Shaft (II)

1. Make sure you have selected impeller and shaft boundaries
2. Click Merge Boundaries to confirm the operation

19. Merge Boundaries - Impeller and Shaft (III)

1. Rename newly created boundary from impeller_merged to impeller
2. Change impeller’s boundary type to wall

20. Split Baffles

Even though we requested the creation of baffles for the rotating_zone, two sides of the baffle can still share some common nodes. In order to make sure that each side has its own nodes, we need to perform the Split Baffles operation on the mesh. This is a very important step when using dynamic mesh model.

1. Expand Options of the default region
2. Select Split Baffles from the drop-down list

21. Create Mesh Interface (I)

In the mesh setup, we requested creating baffles for rotating_zone, so that it can be a slip surface for the dynamic mesh. Now we will create the interface between the baffles.

1. Hold Ctrl key and select rotating_zone and rotating_zone_slave
2. Click Create Arbitrary Interface

22. Create Mesh Interface (II)

After creating an arbitrary mesh interface we need to change its type.

1. Select newly created interface
2. Set type of Transform to Rotational

23. Setup Solver

We will use the Inter (interFoam) solver. This solver is able to model two-phase flow with free surface and supports dynamic mesh capabilities.

1. Go to Setup panel
2. Select Transient filter
3. Select Dynamic Mesh model filter
4. Pick Inter (interFoam) solver
5. Select solver

24. Dynamic Mesh

We will apply a rotational speed of 2 revolutions per second to the zone with the impeller. Due to the orientation of our geometry, our rotation axis will be the -Z-axis of the global coordinate system.

1. Go to Dynamic mesh panel
2. Select Rigid type
3. Check Move selected zone
4. Make sure rotating_zone is selected as Cell Zone
5. Expand Motion options
6. Set Axis [-] to 0 0 -1
7. Set rotational speed Omega [rad/s] 12.56

25. Turbulence

For turbulence modeling we will use Realizable k-ε model.

1. Go to Turbulence panel
2. Select RANS turbulence formulation
3. Select Realizable k-ε model

26. Boundary Conditions - Impeller (Flow)

We need to make sure that impeller velocity is taken from the properties of the rotating zone. For this purpose, we need to apply the Moving Wall Velocity boundary condition.

1. Go to Boundary Conditions setup
2. Select impeller boundary
3. Change velocity type to Moving Wall Velocity

27. Geometry - Initial Conditions Patch

As an initial state, we want the mixing tank to be partly filled with water. For this purpose, we need to create geometry to indicate the initial water location.

1. Go to Geometry panel
2. Click Create Cylinder
3. Rename cylinder_1 to water_patch
4,5. Define cylinder origin, length, and radius

Origin [m] 0 0 -0.18

Length [m] 0.45
Radius [m] 0.6

28. Initial Conditions - Patch

For initial conditions, we will leave all the default values, except inside the water patch, where the water phase fraction will be different.

1. Go to Initial Conditions panel
2. Switch to Patch tab
3. Select water_patch geometry
4. Enable initialization on water_patch
5. Expand Fields list
6. Select αphase1 fraction for initialization
7. Set αphase1 to 1

29. Run - Time Control

We will now adjust the time controls in order to capture the motion of the moving mesh in the output files. We will also enable automatic time step control for the simulation with reduced Courant number for better convergence.

1. Go to Run panel
2. Set Simulation Time [s] to 1
3. Change Time Stepping to Automatic
4. Set initial time step, time step limit and Courant number accordingly

Initial Δt [s] 5e-03
Max Δt[s] 1e-02
Max Co 0.5

30. Run - Output

Now we just have to specify the frequency of writing results to the disk and start the simulation.

1. Switch to Output panel
2. Set Write Control Interval [s] to 1e-02
3. Run Simulation

31. Monitor Solution - Residuals

32. Calculate Additional Fields

When the simulation is finished we want to calculate additional flow variables to use later for postprocessing.

1. Go to Calculate panel
2. Select Full Time Range
3. Select Vorticity field
4. Click Calculate

33. Start Postprocessing - ParaView

Start ParaView when the simulation is finished. Optionally you can start ParaView when the simulation is still in progress to observe the intermediate results.

1. Go to Postprocessing panel
2. Start ParaView

34. ParaView - Load Results

After opening ParaView, we have to load the results of the simulation.

1. Select your case mixing_tank.foam
2. Click Apply
3. Click Last Frame
4. Click Rescale to Data Range
5. After rescale the contour will be shown in the 3D window.

35. ParaView - Coloring (I)

We can change the coloring scheme in ParaView to have nicer colors.

1. Click Edit Color Map from the menu placed on the left side, if the panel is not already shown.
2. Select Choose Preset from the Color Map Editor placed by default on the right side of the ParaView

36. ParaView - Coloring (II)

We can now select a new Color Preset.

1. Choose Rainbow Uniform preset.
2. Apply changes
3. Close Choose Preset window

37. ParaView - Display Water Surface (I)

We will now plot the water surface colored by the water height.

1. Create Contour
2. Select phase fraction alpha.phase1 field as a contour variable
3. Define water surface threshold at 0.01
4. Click Apply

38. ParaView - Display Water Surface (II)

1. Select contour coloring variable p_rgh
2. Set contour opacity to 0.5
3. After change coloring variable and opacity the contour will be shown in the 3D window.

39. ParaView - Calculator (I)

1. Select mixing_tank.foam
2. Clcik Calculator

40. ParaView - Calculator (II)

1. Change name to magVorticity
2. Write mag(vorticity)
3. Click Apply

41. ParaView -

1. Select Calculator 1
2. Create Contour

42. ParaView -

1. Select magVorticity as a contour variable
2. Set contour value 15
3. Click Apply

43. ParaView -

1. Select contour coloring variable U

44. ParaView - Load geometry (I)

1. Select mixing_tank.foam
2. Click Open

45. ParaView - Load geometry (II)

1. Click mixing_tank
2. Select mixing_tank.foam from file selection dialog
3. Click OK

46. ParaView - Load geometry (III)

1. Select bottom, impeller and shaft zones to plot
2. Click Apply

47. ParaView - Load geometry (IV)

1. Set Coloring to Solid Color

48. ParaView - Results

The results are displayed in the graphics window

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