3D Printing

How to 3D print fluid flow trajectory lines

Pressure, temperature, and velocity parameters can now be vividly observed in a 3D printed model.

Arvind Krishnan, manufacturing applications engineer, GoEngineer

Computational fluid dynamics (CFD) software is widely used to determine fluid flow. Typically, the most important information is how variables such as density, velocity, and temperature change as the fluid flows inside or around the structure.

3D printing lets engineers create models that brilliantly display flow simulations that can be used for product demonstrations or at trade shows to describe designs more vividly. The lines in the model depict the flow of fluids, and different colors indicate changes to key variables.

Globe valve example
Figure 1 shows a CAD model of a globe valve. The left side has an inlet with mass flow rate defined, and the right side indicates atmospheric pressure.

Figure 1: CAD Model of a Globe Valve

Flow trajectory data are analyzed using images and animations within the CFD software.

In Figure 2, the flow of water is analyzed and the trajectory lines for velocity distribution are displayed. The range of colors between blue and red represents slower to faster velocities.

Figure 2: Flow Trajectories Showing Velocity Inside a Globe Valve

Exporting trajectory lines
Some CAD software packages, such as SOLIDWORKS Flow Simulation, can export the trajectory lines as curves that can be used to create solid bodies. To represent multiple colors, a single curve might entail four or five different solid bodies since each solid body must be a unique color (Figure 3). The fluid volume can also be exported as a separate solid body. This body represents the entire space inside the structure where the fluid can flow.

Figure 3: CAD Model Showing Solid Bodies of Flow Trajectory Lines

The volume occupied by the solid bodies representing the flow trajectories is subtracted from the fluid volume to ensure there is no overlap. This completes the creation of the structural geometry; its trajectories are ready for 3D printing. (The assembly file is saved in STL format.)

3D printing the model in color

A Stratasys Connex3 printer is used to 3D print the model in Figure 4 in approximately 18 hours. The Connex3 uses PolyJet technology, which can print in a variety of materials. PolyJet 3D printing is similar to inkjet printing, but instead of jetting ink onto paper, PolyJet 3D printers jet layers of curable liquid photopolymer onto a build tray.

Figure 4: 3D Printed Flow Model Showing Trajectory Lines of a Globe Valve

The Connex3 printer can print three colors or any mixture of the three colors. The three colors used in this example are Vero Clear, Vero Yellow, and Vero Blue. The engineer assigns colors for each of the solid bodies from this palette.

Creating a CAD model with solid bodies is an elaborate process. However, the end result is a transparent 3D printed part that shows, with easily distinguishable colors, the details of how fluid flows inside a given geometry or around it.

Best uses of 3D printed flows
3D printed models of flow trajectories are more likely to be used for sales and marketing purposes. However, the value to the product development process should not be overlooked. When everyone on the team can see a physical example of the problem they are trying to solve, it often generates new ideas and approaches to more efficiently solve the problem at hand.

GoEngineer
www.goengineer.com

Arvind Krishnan, manufacturing applications engineer,  GoEngineer, focuses on finite element analysis and 3D printing. He completed his master’s degree in mechanical engineering at North Carolina State University with a thesis in Using Michell Truss Principles to find an Optimal Structure Suitable for Additive Manufacturing.