User Guide: Fluid flow simulation through a centrifugal pump
This user guide demonstrates how to use SimScale to simulate (incompressible) fluid flow through a centrifugal pump. The complexity of this use case results from the requirement of modeling a rotating region. Rotating regions require additional preparation steps for both the meshing and simulation setup which we will cover in the context of this tutorial.
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.
Before starting work on a fluid flow analysis with rotation, we need to make sure to prepare the CAD model to be compatible with this kind of analysis.
Take a look at the provided CAD model. It contains two regions (Change the render mode of the viewer to see the Rotating region body that is contained in inside of the flow region):
The first part represents the fluid region within our model. Essentially the volume that the fluid passing through the pump occupies.
The second part represents rotating region it is just a simple cylinder, which needs to be defined as a CAD part in order to define the rotating region in your fluid domain.
Besides those two basic requirements, there are some more recommendation when it comes to the preparation of the CAD model:
Ensure that the imported geometry consists of Solid parts and not sheet/surface elements.
Remove any small fillets or faces which are insignificant for the analysis.
After making sure that the geometry is prepared for simulation, we can start to set up a simulation.
To create a new simulation, click on the “+” button next to ‘Simulations’ in the tree or the “Create Simulation” button on the geometry panel.
Select the “Incompressible” analysis type and click “Create Simulation“.
Assign the standard air material to the fluid domain as shown below:
Assign the standard air material to the fluid domain
Default values for initial condition parameters are usually enough. If these parameters estimated correctly, the solution will converge faster.
You need to assign four boundary conditions: Inlet, Outlet, Walls and a Rotating Region. The following image shows an overview of them:
The pump inlet needs to be assigned an inlet velocity boundary condition and the inlet velocity is as given below.
The outlet of the pump needs to be assigned a pressure outlet boundary condition.
All physical walls need to be assigned as walls
Click on the ‘+’ icon next to rotating zones under Advanced concepts
Define the MRF rotating zone and select the rotating region as shown below:
The default settings in numerics are suitable for this simulation, so we don’t have to worry about them.
The Simulation Control settings define the general controls over the simulation. The following controls should be applied:
It is important to monitor the convergence of pressure values on the inlet and outlet faces. We monitor the surface average data on the inlet and outlet faces. The settings are shown below:
Left click on the mesh icon to create a new mesh.
Choose the Hex-Dominant (only CFD) Algorithm.
Keep the meshing mode to Internal, the sizing option as Automatic sizing, the Fineness as Coarse and thenumber of processors to Automatic.
The general cell size for the mesh is being calculated by the mesh algorithm. Additionally you need to specify the following refinements:
A Region Refinement for the rotating zone
Two Surface Refinements (One at the rotor blades and one on the rotating zone)
Boundary Layers to all surfaces representing physical walls.
Region Refinement for the Rotating Zone
A region refinement is used to refine the mesh within a volume. The cylinder around the propeller will define a zone within the cells will be more refined than in the rest of the mesh.
Click on the ‘+’ icon next to Refinements and add an region refinement.
Select the Refinement mode as ‘inside’ and the Maximum edge length of refinement as ‘0.001’.
Select the rotating region for region refinement as shown below:
Set up region refinement in the rotating region to get a more refined mesh
Surface Refinement for Blade surfaces
In order to have a finer mesh over the surface of the body, we add surface refinement.
Add a new refinement and select surface refinement.
Select the impeller surfaces and define the minimum and maximum length as 0.001.
Set up surface refinement on the blade surfaces
Surface Refinement for the rotating (MRF) zone:
This step is crucial to correctly define the cell zone which will rotate.
Add a surface refinement and set the ‘Cell Zone’ option to ‘With Cell Zone’
Keep the minimum and maximum levels at 0.001.
Select the rotating region for the refinement Set up the surface refinement for the rotating region
Boundary Layer Refinement:
Layer refinements are used to create boundary layers near solid walls. When considering turbulent effects, boundary layer refinement is required in order to obtain a correct solution.
Create a new layer refinement and assign all faces of the propeller and the pipe outer surfaces This can be done by hiding the rotating region and using active box selection to select all the surfaces and deselect the inlet and outlet surfaces
Select the Inflate Boundary layer setting and the below values. Set up the boundary layer refinement and select all the faces on the impeller and the pump outer surfaces.
Now you can either generate the mesh or start the simulation right away. In the second case the mesh will be generated automatically. The mesh generated will have about 3 Million cells and look like the one in the picture below.
You can click on generate mesh clip to inspect the internal mesh. Adjust the settings of the normal. Click on generate mesh clip icon. Generate mesh clip showing the region refinement in the rotating region.
Click on the ‘+’ icon next to simulation run and start the simulation.
Once the simulation has finished, click on solution fields icon under the convergence plot icon to open the post processor. Click on results and select pressure to view the pressure field on the entire domain. Pressure field throughout the domain.
It is clearly seen that the inlet pressure is negative implying that the impeller is imparting a pressure head to the fluid.
Select the cutting plane in the x direction and select the scalar and vector as velocity to see the velocity contours and vectors
The rotating region clearly shows the rotating fluid inside it.
We can view the path tracked by the fluid particles by clicking on the ‘+’ icon next to particle traces and selecting the outlet face for seeding as shown below: Generate the particle traces by picking the outlet face for seeding
Click on velocity to map the scalar and to compute the vector Generate the particle traces by mapping them to velocity scalar
Last updated: March 11th, 2020
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