1. Download SimFlow
SimFlow is a general purpose CFD Software
To follow this tutorial, you will need SimFlow free version, you may download it via the following link:
Download SimFlow
2. Create Case
Open SimFlow and create a new case named droplet
Go to
New
panelProvide name droplet
Click
Create Case
to open new project

3. Meshing parameters
We will start by creating a 2D mesh. This can be accomplished by choosing the Plate
type as the background mesh.
Go to
Hex Meshing
panelGo to
Base
tabSelect
Plate
as aBase Mesh Type
Define minimum and maximum extend
Min \({\sf [m]}\)00Define the number of divisions
Division8080Change boundary type to
wall
for all background mesh boundaries

4. Start Meshing
We will start by creating a 2D mesh. This can be accomplished by choosing the Plate
type as the background mesh.
Now we are ready to create our simple mesh.
Go to
Mesh
tabPress the Mesh button to start meshing process

5. Mesh
After the meshing process is finished, the mesh should appear in the graphics window.
Click ViewXY or press CTRL+F1 to orient view plane
Click Fit View to zoom the geometry

6. Create Geometry - Droplet
To indicate the initial shape of the droplet we will use cylinder geometry.
Go to
Geometry
panelSelect Create Cylinder
Change geometry name from
cylinder_1
to dropletSet the origin
Origin \({\sf [m]}\)0.250.4-0.1Set the cylinder dimensions
Length \({\sf [m]}\)0.2
Radius \({\sf [m]}\)0.025

7. Create Geometry - Water
Additionally, we would like the droplet to fall down into the tank partially filled by water. To fill the bottom part of the domain with the water we will add another geometry.
Add a new geometry by clicking Create Box
Change geometry name from
box_1
to waterSet the origin and box dimensions
Origin \({\sf [m]}\)00-0.1
Dimensions \({\sf [m]}\)0.50.20.2

8. Create Geometry - Water Refinement
To be able to better resolve water behavior, we will create an area with a higher mesh resolution. To do this, we will add two more box geometries.
Select Create Box
Change geometry name from
box_1
to water_refinementSet the origin and box dimensions
Origin \({\sf [m]}\)00-0.1
Dimensions \({\sf [m]}\)0.50.30.2

9. Create Geometry - Droplet Refinement
The second refinement box will be located at the path of the falling droplet.
Select Create Box
Change geometry name from
box_1
to droplet_refinementSet the origin and box dimensions
Origin \({\sf [m]}\)0.20.3-0.1
Dimensions \({\sf [m]}\)0.10.20.2

10. Refine Mesh (I)
Go to
Mesh
panelExpand the
Options
list next todefault
regionSelect
Refine

11. Refine Mesh (II)
Check the refinement regions
droplet_refinement
water_refinement
Uncheck the Z axis in
Refinement Directions
Click Refine

12. Display Mesh
Check the refinement region by hiding the geometries and displaying mesh.
Click Graphic Object List
Uncheck
Geometry
To hide the Graphics Objects panel press the Esc key. |

13. Select Solver - Inter
To analyze water behavior we will use Inter (interFoam) solver. This solver designed to model two-phase flow with interface capturing capabilities.
Go to
SETUP
panelSelect
Transient
filterSelect
Multiphase
model filterPick
Inter
(interFoam) solverClick Select button to confirm

14. Transport Properties - Water
Now we will define the transport properties for both fluids.
Go to
Transport Properties
panelChange phase name from
phase1
to waterOpen Material Database
Pick up
water
from the listClick Apply

15. Transport Properties - Air
Repeat this step for phase2
using air properties.
Change phase name from
phase2
to airOpen Material Database
Pick up
air
from the listClick Apply

16. Operating Conditions - Gravity
Go to
Operating Conditions
panelDefine gravitational acceleration along negative Y-axis
g \({\sf [m/s^2]}\)0-9.810

17. Initial Conditions - Droplet
We will use the droplet
geometry to select the region where water phase fraction should be initially applied.
Go to
Initial Conditions
panelSwitch to
Patch
tabEnable initialization on
droplet
Expand Fields list
Select \(\alpha_{water}\) fraction for initialization
Set initial value of \(\alpha_{water}\) to 1

18. Initial Conditions - Water
Repeat the step for water geometry.
Enable initialization on
water
Expand Fields list
Select \(\alpha_{water}\) fraction for initialization
Set initial value of \(\alpha_{water}\) to 1

19. Monitors - Create Slice
During calculation, we can observe intermediate results on a section plane. To add sampling data on a plane we need to define plane properties and also select variables that will be sampled. Note that runtime post-processing can only be defined before starting calculations and can not be changed later on.
Go to
Monitors
panelSwitch to
Sampling
tabSelect Create Slice
Expand Fields list
Check U and \(\alpha_{water}\)

20. Run - Time Controls
For any simulation, it is very convenient to let the solver automatically determine the proper time step value. To use this option we need to define time step constraints by providing the initial time step(adjusted by the solver during computations), maximal time step value and the Courant number. In our case, we will reduce the default Courant number for better stability and quality.
Go to
RUN
panelChange
Time Stepping
toAutomatic
Set initial time step, time step limit and Courant number accordingly
Initial \(\Delta t\) \({\sf [s]}\)5e-03
Max \(\Delta t\) \({\sf [s]}\)0.1
Max Co \({\sf [-]}\)0.5

21. Run - Output
It is very important to control when results should be stored on the hard drive. This is especially important for the transient simulations where users are interested in the whole flow history saved as a collection of the snapshots.
Switch to
Output
tabSet
Write Control
Interval [s]
to 0.02
(solver will store results on the hard drive every 0.02 second of the simulation)Click Run Simulation button

22. Results
When calculations will begin SimFlow automatically will switch view to the Residuals
tab, where we can observe the convergence of our simulation. This is very handy for steady-state simulations when we try reaching low residuals levels. In case of transient simulation, we would rather like to see how our flow develops as simulation time progress.
Switch to
Slices
tabChoose alpha.water field
Click Adjust range to data
Play with an animation buttons to track the results of analysis
