When it comes to high-performance engines, Computational Fluid Dynamics (CFD) has really advanced our understanding of how an engine performs. While the pioneers of our sport used pieces of string and their own appendages to learn about how everything flowed, CFD has taken that knowledge and expanded it, exponentially.
In a recent EPARTRADE webinar, Dan Agnew, Principal Engineer at EngSim Corporation gave us a peek behind the curtain at what OEM-level CFD software is capable of processing.“EngSim works with engine development efforts throughout the industry, including performance applications,” says Agnew. “The company provides engine modeling and simulation services for the client. It’s not just software. In fact, we’re users, not developers of the software.”
CFD Isn’t Magic
One thing Agnew was very upfront about, is the fact that computer modeling is never used instead of actual physical testing, but as one of the steps in development. “This isn’t a replacement for good design and testing, but rather a supplement to it. This allows real-world testing to be much more targeted and efficient. This kind of analysis takes a deep dive into why something works, or doesn’t work.”
What CFD allows is a lot of things to be tested and iterated without manufacturing or altering a single part, at least not in the physical realm. “You can take thousands of crazy ideas, and then filter out the bad ones,” says Agnew. “We’re working with a team right now that has about 100 new cam designs they want to test. Physically testing 100 cams is not very practical, so we’ll filter all of those down to a few cam designs to actually test. You get so much data out of this, you can spend weeks poring over the data from one run.”
While most of us associate CFD with intake and exhaust airflow, there are a huge number of areas where it can be used within an engine program. Basically, anywhere a fluid is used. CFD can be used to evaluate coolant flow distribution throughout the block and cylinder head, and optimize head gasket design. It can model how coolant will transfer heat as well as the pressure of the coolant as it moves through the block. It can also model the combustion process in the cylinder, degree by degree (of crankshaft rotation).
How The Iteration Process Works
Let’s take a look at a hypothetical cylinder head development program. The CFD analysis will supplement the actual flow bench testing, but, by doing the analysis before testing, they are much closer to the final product once they are on the flow bench. The beginning of the CFD testing is a 1D simulation that determines pressure for testing, where in the design to optimize, and then the effects of the changes on the engine.
“Test pressure on a flowbench is typically 28 inches of water, but in the real world, that can be an unrealistic pressure. This is especially true on the exhaust side,” explains Agnew. By running the simulation, they can see the approximate pressures of the intake and exhaust charges at various points, and tailor physical testing around those parameters.
Then, the design team identifies where they will see the most benefit from improving flow. “By plotting mass flow against valve lift in the specific application, you can identify where the most benefit can be gained. Typically, that means I want to focus on the low-to-mid lifts on the exhaust side, and the opposite for the intake,” Agnew says.
Starting with a 3D CAD model, a meshed model is created for testing, along with specific section views. From there, the testing universe is created, with intake inlet and outlet pressures established at various valve-lift conditions. On the exhaust, the same is done. “With these kinds of models, you have the flexibility to test things like Atkinson cycle, pretty easily,” shares Agnew.
All this data allows an experienced cylinder head developer to really cut down on both the quantity of flowbench testing that needs to be done, as well as the number of wild goose chases. “Being able to show a flowbench technician one of these graphs is usually incredibly eye-opening for them,” says Agnew. “They can stick their finger in the port, or use probes, but they don’t ever get the chance to see the airflow like this. Once they see it like this, they are able to go back and make changes to the port much more efficiently.”
CFD has come a long way since its early days, thanks both to the huge leaps we’ve made in computing power available to the average person, as well as engineers pouring their whole being into constantly refining the physics models. It now allows companies like EngSim to save their customers months, if not years, of research and development efforts, by allowing them to focus their efforts where they will make the most difference.