Tutorial 2: Incompressible water flow through a pipe junction


In this tutorial, we will carry out a fluid flow simulation of water flowing through a pipe junction. The objective is to get insights of the flow field at the junction of the pipe. There are two inlets and one outlet for this configuration. The simulation will show if there is a recirculation area near the junction and if the design needs to be optimized accordingly.

streamlines inside the pipe

Figure 1: Streamlines of water flow inside a pipe junction


The tutorial project “Tutorial 2: Incompressible water flow through a pipe junction” has been imported and is open in your SimScale Workbench.
You will learn the following in about 5 minutes:

I. Simulation Creation

You will try to setup a steady-state flow simulation to obtain an average flow field inside the pipe junction. You will learn how to assign the materials and boundary conditions and leave the other settings as default.

  1. Once the Workbench is open, you will see the CAD model Pipe Junction Model being loaded in the viewer.
  2. To create a new simulation, click the 'Create Simulation' button.
    how to start creating a simulation in simscale

    Figure 2: Creating a simulation in SimScale by clicking the 'Create Simulation' button.

  3. Select 'Incompressible' as the Analysis Type
    Note: Always choose Incompressible in cases where velocity and temperature gradients are small, independent from your material choice.
    available analysis types in simscale

    Figure 3: Select 'Incompressible' for your pipe junction simulation and press 'Create Simulation' to start setting up the simulation

  4. A new Simulation tree will automatically be generated on the left side of your screen, containing all the parameters and settings required to run the simulation.

II. Material Assignment

  1. To assign a new material, click on the '+' button next to Materials in the simulation tree.
    selecting materials in the simulation tree

    Figure 4: Selecting Materials from the Simulation Tree to select fluid inside the pipe junction

  2. This will open the Material library which contains all the available materials for a simulation. Scroll down to select 'Water' and click 'Apply'.
    selecting water in the material library

    Figure 5: Select 'Water' from the available list of fluids

  3. Water will be automatically assigned to the pipe volume.
    Note: The color blue indicates that you are in assignment mode.
    available analysis types in simscale

    Figure 6: After selecting, Water will then be assigned as the fluid inside the pipe volume

III. Boundary Conditions Assignment

Boundary conditions are constraints that define the physical boundaries of the simulation, such as the input and output of a pipe. For this simulation, three boundary conditions(Velocity inlet 1, Velocity inlet 2 and Pressure outlet 3) will be necessary so that we can model water meeting at the junction of the pipe coming from the horizontal and vertical inlets.

boundary condition overview of pipe flow simnulaton

Figure 7: Overview of boundary conditions

  1. Add Velocity inlet 1
    1. To create a new boundary condition, click on the '+' button next to Boundary conditions in the simulation tree. Select 'Velocity inlet' from the list.
      setting up boundary conditions

      Figure 8: Choosing boundary conditions in the Simulation tree

    2. Set the velocity in z-direction to '-1.5' m/s. This will assign a flow with the specified velocity to the assigned face. In this case, flow from the negative z-direction is needed to model the horizontal flow. The global coordinates can be found in the viewing cube in the bottom right of your screen.
    3. Select the horizontal face in the viewer. This will assign the face as a velocity inlet.
      setting up a velocity inlet boundary condition

      Figure 9: Setting up a velocity inlet boundary condition for horizontal flow

  2. Add Velocity inlet 2
    1. We will set up another velocity inlet to simulate a vertical flow by following the same steps as before.
    2. Set the velocity in y-direction to '-1' m/s. Select the face to assign the new velocity inlet.
      setting up a second velocity inlet

      Figure 10: Setting up a second velocity inlet boundary condition for the vertical flow

  3. Add Pressure outlet 3
    1. Last but not least, we will add a third boundary condition which is the 'Pressure outlet'.
    2. Select the face to assign it as a pressure outlet boundary condition.
      setting up a pressure outlet

      Figure 11: Setting up pressure outlet boundary condition for a pipe junction

IV. Simulation Run

Now you are ready to start your first simulation run. The Numerics and Simulation Control settings are set by default and do not have to be changed for this case.

  1. Create a simulation run by clicking on the '+' button next to Simulation runs in the simulation tree.
    start running a simulation

    Figure 12: Starting a simulation run in SimScale

  2. In the New Run dialog click 'Start' to start the simulation run. (The simulation run will take some time to finish.)
    running a simulation

    Figure 13: New run dialog with resource estimate for pipe junction flow simulation

  3. Once the simulation run is finished, click 'Post-process results' or 'Solution Fields' under the run to open the post-processor.
    running a simulation

    Figure 14: How to get to SimScale's integrated post-processor

V. Simulation Results

  1. The cutting plane will be automatically applied. Now, we want to show the flow inside the pipe. Therefore, we will change the orientation of the plane in the x-axis. Click on 'X' besides Orientation (Normal) to change the orientation of the cutting plane.
    Note: Turn the model in the viewer to see cutting plane properly.

    applied cutting plane

    Figure 15: Pipe flow junction cut in half with cutting plane in the x-plane to show the velocity magnitude contours inside the pipe junction

  2. You can also find areas where recirculation occurs by visualizing the velocity vectors. Turn on the toggle beside Vectors to show the velocity vectors. Next, to make the vectors more clear, you can set the color of the vectors to black beside Coloring.
    visualizing vectors on a cutting plane

    Figure 16: Velocity vector settings to help show recirculation areas

Based on the velocity vectors, we can see that recirculation occurs in the areas near the junction, so the design of the pipe will need to change near these areas. For further post processing please visit this tutorial: Post-processing Fluid Flow Simulations

Congratulations! You just finished your first internal fluid flow simulation on SimScale!

Find more tutorials in SimScale's documentation: SimScale Tutorials and User Guide