A couple of weeks ago, I had the pleasure of conversing with Desktop Engineering magazine’s senior editor Kenneth Wong for a podcast recording. He had a simple challenge for me: For a structural engineer who is just beginning to work with fluid dynamics, outline the points important to CFD flow simulation. Additionally, he asked me to explain how to avoid pitfalls when setting up the simulation and what to look for when analyzing the results.
My first thought was that, well, there are great classes, training and free YouTube videos available. Give me a couple of hours and I can turn a structural-expert-but-CFD-newbie into a CFD user. Kenneth understood all this, but his biggest challenge was yet to come. He asked me quite seriously, “And can you get an engineer on the right track in a couple of minutes?”
*** Mission Impossible soundtrack playing inside my head **** Sure! Let’s do it!
Part 1 of the mission: Select an example that is relevant to a structural engineer. We decided to discuss a valve design and the pressure that is exerted by the flow, making sure that the pressure is not high enough to cause structural damage.
Part 2 of the mission: Identify tips and tricks to help engineers avoid typical pitfalls. We decided to focus first on the simulation setup. (Analysis results will be discussed in a future podcast.)
1) Structural engineers have experience studying the structure of the valve. To look at fluid behavior, they need to look at “negative” space of the device — the flow inside the valve and pipe system.
2) Mesh requirements for a fluid simulation are very different than that for a structural simulation. Let’s make sure we tell the CFD newbie how to correctly resolve key aspects of the flow features — near-wall regions (where the flow velocity drops to zero) and regions where the flow curls and swirls (near the valve).
3) Since 99 percent of industrial flows are turbulent, you must understand how to best set up the turbulence model. As there is no single model that will work for all industrial flow, ANSYS software provides many models. Online forums, classes and simulation software providers like ANSYS provide tips and best practices to help engineers master this hurdle.
4) Set up boundary conditions. In this case, there is no need to simulate each meter of piping, so we focus on the valve itself. For this part, the boundary conditions are key: If they are not set properly, the GIGO (garbage in, garbage out) principle kicks in. So we need to be very particular about how to set up inflow and outflow boundary conditions. On the thermal side, we show that special models exists to treat conduction of heat through the pipe and valve material without actually having to simulate the actual process using a structural simulation.
You can listen to the full podcast discussing the simulation setup and let me know if you have experienced any challenges in doing this type of simulation.
And if you want even more information about CFD, check out some free online classes hosted on YouTube.
You can also see how an entire workflow can be executed here in this video.
Have happy and successful simulations!