Setting Up a Pipe Flow Simulation with Line Probes: A Step-by-Step Guide

Welcome back to our CFD Simulation Using SolidWorks blog series! In this blog, we’re tackling a highly requested topic — setting up a pipe flow simulation using SolidWorks Flow Simulation, combined with the use of line probes to measure crucial variables like velocity and shear stress. We’ll also cover how to run a parametric study to see how changes in mesh resolution affect simulation accuracy. 

Step 1: Creating the Geometry for the Pipe 

Let’s begin by creating the geometry for the pipe. For simplicity, we’re going to create a 1-meter-long pipe. The steps to create this geometry in SolidWorks are as follows: 

1. Start with a Circle: Begin by sketching a circle on the top plane, which will serve as the cross-section of the pipe. This step can be done quickly by selecting the Circle tool in the sketch interface. 
2. Extrude the Circle: Once the circle is drawn, extrude it to a length of 1 meter. This will form the main body of the pipe. The diameter of the pipe can be arbitrary or based on a real-world scenario. 
3. Add Wall Thickness: Use the Shell feature to give the pipe a realistic thickness. Select the top and bottom faces of the extruded pipe and add a wall thickness (e.g., 1 mm). This shelling process ensures that the pipe is hollow inside, allowing for fluid to flow through it. 

At this point, you have the basic pipe geometry, and we’re ready to move on to setting up the flow parameters and probes. 

Step 2: Adding Line Probes for Flow Analysis 

Once the pipe geometry is ready, we need to add line probes to measure variables like velocity and shear stress at different locations within the pipe. These probes allow you to gather detailed data on how the fluid behaves as it flows through the pipe. 

1. What Are Line Probes? 

Line probes are virtual lines that can be placed at specific locations in your geometry to measure key flow variables along that line. They’re particularly useful for visualizing how the flow evolves as it moves through different regions of the pipe. 

2. Placing the Line Probes: 

Place the first line probe near the outflow boundary (the exit of the pipe) where you expect significant flow development. We can set this probe 0.05 meters from the exit. Then, place a second line probe slightly behind the first one, say at 0.1 meters from the exit. These two probes will allow us to observe how the flow properties change as the fluid exits the pipe and compare the results at different distances from the outflow. 

Step 3: Setting the Boundary Conditions 

The next step is to define the boundary conditions for the simulation. Boundary conditions dictate how the fluid enters and exits the pipe and what happens at the walls. Here’s how to set them up: 

1. Outlet Boundary Condition: 

The outlet will be set to a static pressure boundary condition. For our simulation, we’ll use 101325 Pa, which is standard atmospheric pressure. This tells the software that the fluid exits the pipe into a normal atmospheric environment. 

2. Inlet Boundary Condition: 

At the inlet, we’ll specify a velocity boundary condition. Set the inlet velocity to 10 m/s. This means that the fluid (such as air or water) will enter the pipe at this velocity, allowing us to study the flow as it moves through the pipe. 

3. Wall Boundary Condition: 

The walls of the pipe will be set as real walls, which means that no-slip conditions will be applied. This ensures that the velocity of the fluid at the wall is zero, accurately representing real-world pipe flow behavior. 

Step 4: Refining the Mesh 

With the boundary conditions in place, we can now create the computational mesh. The mesh divides the pipe into smaller elements where the flow equations are solved. A well-refined mesh is crucial for accuracy, so we’ll manually adjust the mesh settings to ensure the best results. 

1. Initial Mesh Settings:

By default, SolidWorks Flow Simulation generates a basic mesh, but we can improve accuracy by manually refining it. A coarse mesh might give you quick results but can lead to inaccurate predictions. For this reason, let’s set 10 grid points along the X and Y axes, which describe the cross-section of the pipe. This will give us better resolution in capturing the flow characteristics. 

2. Refining Along the Length of the Pipe (Z-axis): 

For the length of the pipe (Z-axis), we’ll reduce the number of mesh points from the default 114 to 50. This still provides good resolution along the pipe length while keeping the computational cost manageable. 

This mesh setup strikes a balance between accuracy and computational efficiency, ensuring that our results are precise without taking too long to compute. 

Step 5: Running the Simulation 

Now that the geometry, boundary conditions, and mesh are ready, it’s time to run the simulation. Once the simulation completes, SolidWorks Flow Simulation will generate the results, which you can visualize through cut plots and line probes. 

1. Velocity Profile: 

By viewing the velocity profile along the length of the pipe, you’ll notice that the velocity changes from the inlet to the outlet. Near the walls, the velocity will be lower due to boundary layer formation, a common phenomenon in fluid dynamics where friction between the fluid and the pipe walls slows the flow. 

2. Shear Stress: 

The line probes will give us data on shear stress, which represents the force exerted by the fluid on the walls of the pipe. This is an important parameter in understanding the wear and tear on the pipe and how the fluid interacts with its surroundings. 

Step 6: Conducting a Parametric Study 

To take our simulation further, let’s run a parametric study. A parametric study allows us to vary certain parameters (like mesh resolution or inlet velocity) to see how the results change. In this case, we’ll focus on varying the number of mesh points along the X, Y, and Z axes to see how mesh refinement impacts the accuracy of our results. 

1. Varying Mesh Points: 

We’ll start with our current mesh setup as the baseline. Then, in the first design point, we’ll double the number of mesh points along the X, Y, and Z axes. In the second design point, we’ll quadruple the number of points compared to the baseline. 

2. Analyzing Results: 

After running the parametric study, you’ll see that as the mesh becomes finer, the velocity profile becomes more refined and accurate. This process, known as a grid dependency test, is crucial for ensuring that your results aren’t skewed by a coarse mesh. As the grid is refined, the simulation results converge to a more accurate solution. 

3. Velocity and Shear Stress Comparison: 

You can compare the results across different line probes and mesh resolutions to see how the flow properties evolve. For instance, as the mesh is refined, the shear stress near the pipe walls might change, giving you a more detailed understanding of how the fluid interacts with the pipe surface. 

Conclusion 

In this blog, we explored the process of setting up a pipe flow simulation using SolidWorks Flow Simulation, complete with line probes to gather velocity and shear stress information. We also ran a parametric study to understand how mesh refinement affects the accuracy of our results. 

The key takeaways here are: 

• Accurate legend setup and mesh refinement are essential for obtaining reliable results. 
• Always use line probes to gather detailed data on velocity and shear stress along different sections of the pipe. 
• Running a grid dependency test helps ensure that your results aren’t dependent on the mesh resolution. 

Hope you found this guide helpful and engaging.  

Stay tuned for the next installment in our CFD Simulation Using SolidWorks blog series, where we’ll tackle more advanced topics and applications.  

This blog is part of our ongoing series on CFD Simulations using SolidWorks.   

If you missed the previous posts, check them out here.

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