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User Guide: Fluid flow simulation through a centrifugal pump

Overview

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.

Import tutorial project into workbench

See the finished project

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.

Geometry preparation

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.

pump geometry
Pump geometry prepared for simulation. It contains the flow region (the volume inside the pump which is occupied by the fluid) as well as a second solid body that defines the rotating region.

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.

Simulation Setup

After making sure that the geometry is prepared for simulation, we can start to set up a simulation.

  1. To create a new simulation, click on the “+” button next to ‘Simulations’ in the tree or the “Create Simulation” button on the geometry panel.
  2. Select the “Incompressible” analysis type and click “Create Simulation“.

Materials

Assign the standard air material to the fluid domain as shown below:

Assigning Air to Fluid Domain

Assign the standard air material to the fluid domain

Initial Conditions

Default values for initial condition parameters are usually enough. If these parameters estimated correctly, the solution will converge faster.

Boundary Conditions

You need to assign four boundary conditions: Inlet, Outlet, Walls and a Rotating Region. The following image shows an overview of them:

Boundary Conditions Centrifugal Pump Tutorial SimScale

  1. The pump inlet needs to be assigned an inlet velocity boundary condition and the inlet velocity is as given below.
  2. The outlet of the pump needs to be assigned a pressure outlet boundary condition.
  3. All physical walls need to be assigned as walls

Assigning Boundary Conditions to Tutorial Centrifugal Pumo

MRF/Rotiang zone

  1. Click on the ‘+’ icon next to rotating zones under Advanced concepts
  2. Define the MRF rotating zone and select the rotating region as shown below:

Define Settings Rotating Zone MRF Tutorial Centrifugal Pump SimScale

Numerics

The default settings in numerics are suitable for this simulation, so we don’t have to worry about them.

Simulation Setup

The Simulation Control settings define the general controls over the simulation. The following controls should be applied:

Result Control

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:

Result Control Settings Tutorial Centrifugal Pump SimScale

Mesh Generation

  1.  Left click on the mesh icon to create a new mesh.
  2. Choose the Hex-Dominant (only CFD) Algorithm.
  3. Keep the meshing mode to Internal, the sizing option as Automatic sizing, the Fineness as Coarse and the number of processors to Automatic.

Mesh Settings Tutorial Sentrifugal Pump SimScale

Refinements

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.

  1. Click on the ‘+’ icon next to Refinements and add an region refinement.
  2. Select the Refinement mode as ‘inside’ and the Maximum edge length of refinement as ‘0.001’.
  3. Select the rotating region for region refinement as shown below:

Region Refinement Rotating Zone Tutorial Centrifugal Pump SimScale

 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.

  1. Add a new refinement and select surface refinement.
  2. Select the impeller surfaces and define the minimum and maximum length as 0.001.
  3. Set up surface refinement on the blade surfaces
Surface Refinement Blades Tutorial Centrifugal Pump SimScale
Set up surface refinement on the rotor surface

Surface Refinement for the rotating (MRF) zone:

This step is crucial to correctly define the cell zone which will rotate.

  1. Add a surface refinement and set the ‘Cell Zone’ option to ‘With Cell Zone’
  2. Keep the minimum and maximum levels at 0.001.
  3. Select the rotating region for the refinement Set up the surface refinement for the rotating region
Surface Refinement Rotating Zone (MRF) Tutorial Centrifugal Pump SimScale
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.

  1. 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
  2. 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.
Boundary Layer Settings Tutorial Centrifugal Pump SimScale
Boundary layer settings

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.

Finished Mesh Tutorial Centrifugal Pump SimScale
Finished Mesh

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.

Cretaing Mesh Clip Tutorial Centrifugal Pump SimScale
How to create a mesh clip

Results

  1. Click on the ‘+’ icon next to simulation run and start the simulation.
  2. 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.
pressure distribution centrifugal pump tutorial SimScale
Vizualize the Pressure distrubution over the surface of the pump
  • 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
Velocity Vectors Section View Centrifugal Pump Tutorial SimScale
Velocity vectors inside the pump
  • 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
vizualize streamlines in centrifugal pump tutorial SimScale
Visualizing Streamlines
  • Click on velocity to map the scalar and to compute the vector Generate the particle traces by mapping them to velocity scalar
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