Tutorial 2: Incompressible water flow through a pipe junction

Step-by-step

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:

• Creating a simulation
• Assigning material
• Applying boundary conditions
• Running the simulation
• Viewing simulation results

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.
   
   

   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.
   

   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.
   
   

   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'.
   
   

   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.
   
   

   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.

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.
      
      

      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.
      
      

      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.
      
      

      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.
      
      

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

IV. Simulation Run

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

   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.)
   
   

   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.
   
   

   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.
   
   
   

   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.
   

   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