CFD cuts development time for a race winning engine
When an engine specialist as experienced as Brian Kurn is excited about a technology, others in the field tend to take notice. If they don't, they should. Kurn is currently in charge of valvetrain development together with all virtual prototyping technologies, including engine and valvetrain simulation, as well as CFD at ECR Engines, a division of Richard Childress Racing. In a career spanning 25 years he has worked for some of the biggest names in the sport, including Roush, Hendrick and with Toyota team Bill Davis Racing. Kurn started his craft building and improving V8 engines for the small dirt tracks and worked his way up to the elite series in NASCAR.
In a career spanning 25 years he has worked for some of the biggest names in the sport, including Roush, Hendrick and with Toyota team Bill Davis Racing. Kurn started his craft building and improving V8 engines for the small dirt tracks and worked his way up to the elite series in NASCAR. "In the 'good old days', so-called tuners determined the biggest valves that could be used and then they simply began to hand-port the head, believing that the more air that would flow, the more power it should make," says Kurn.
"After spending a lot of time doing this, you took the parts to the dyno and only then did you find out if you had found a solution or just scrapped another cylinder head," he continues. "It was an expensive and time-consuming way to see if your idea gained a few horsepower or not. And each time you got a new head design, you really had to start again."
It was this inefficiency which drove the forward-thinking Kurn to investigate simulation technologies. Now, as an experienced CFD user, primarily to analyse internal flows in the engine, both stand-alone and coupled with Engine Simulation, Kurn is at home with state-of-the-art technology. But in those early days, just over a decade ago CFD posed problems. "The run-times to do the simulations took too long and when we had to create our own mesh, we really suffered with the variability between users," claims Kurn. "It can affect your results, introducing inconsistency, and ultimately your trust in the data can go out of the window."
Even today, creating a good mesh is crucial to resolve the flow. But the quest for an automatically generated mesh never quite delivered the accuracy needed to move away from user-generated data. For years, engineers simply accepted the challenges and did what little they could to minimise the variations. For Kurn, it was a frustration. "I never believed that an effective automatic meshing tool would happen in my lifetime. I thought we would be stuck with the longer run-times forever," he explains. But after learning that Converge had a collaborated with engine simulation provider Gamma Technologies, everything changed.
It was there Kurn first encountered an innovative automatic meshing solution called CONVERGE CFD Software. Developed by Madison, it automates the meshing at run time with a perfectly orthogonal Cartesian mesh that eliminates the need for a user-defined mesh.
Written by engine simulation experts to address the deficiencies of other CFD codes, CONVERGE offers run-time grid generation and refinement so users such as Kurn no longer need to spend their time creating meshes. Instead, the user supplies a triangulated surface and a series of guidelines from which the CONVERGE proprietary code creates the grid at run-time. "They had hit on my objective; reduce the run-time whilst retaining the accuracy of the simulation, removing assumptions." says Kurn. "Testing would become more fruitful as with consistent meshing and we could test more solutions in the same timeframe."
For race teams, the software achieves the one thing that is hard to buy - more time - and Kurn has been astounded with the amount he's saved. "We gained literally weeks on some developments in 2014," he claims. "On our Daytona Prototype engine we got ahead of the development schedule and we were able to start testing different trumpet lengths before the engine was even ready to run on the dyno, or got anywhere near the car. This saved not only time but also the number of prototype parts produced. Knowing the exact parameters of key items such as combustion chamber, intake and exhaust ports means now when we make changes, we can accurately measure just those changes and have complete control over them. We now run a number of simulations and with the accurate data generated can confidently pick the best one or two to try on the car."
Trumpet design is just one of the areas that Kurn is trusting to CONVERGE. Others include the very challenging modelling of combustion and he sees the potential for using CONVERGE for optimising future fuel efficiency. Rob Kaczmarek, marketing director from Convergent Science, explains: "Our Genetic Algorithm Optimisation can run cases depending on design parameters such as fuel efficiency or power and think outside the box."
A common area of interest where this approach works particularly well for is in-cylinder flame propagation. Kaczmarek believes non-CONVERGE users really struggle with hard-to-define areas like this. "It leads them to either go to a larger-sized mesh, maybe up to 1mm in order to save time but losing accuracy, or go to a smaller mesh increasing the accuracy but also increasing run-times," claims Kaczmarek.
The good news is CONVERGE can take care of this, allowing the programme to refine the mesh when and where it is needed at run-time for more accuracy all while keeping run times manageable. In addition, the software also comes equipped with detailed chemistry and physical models to help engineers make gains.
"For example, measuring turbulence of a flame in microseconds and how it changes is very hard to do but crucial for efficiency," adds Kaczmarek. "CONVERGE can help. It's great for transients and we saw, for example, with the use of direct injection in Daytona Prototypes and other high pressure scenarios, CONVERGE is very effective. Even though NASCAR engines have been around for a long time some of the best tuners who think they have understood them can now really see and what is actually happening for the first time."
Convergent Science Inc
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