There’s an old project management adage that goes “Good. Fast. Cheap. Pick any two.” There are tons of websites and blogs about it. I’m particularly fond of this one about the designer’s holy triangle. Unfortunately, this holds true in the engineering simulation world. With “good” meaning “accurate,” you’re stuck with suboptimal choices: Good + fast = expensive; good + cheap = slow; fast + cheap = inferior. Product designers are stuck with good results that take too long or “directional” results fast. Good and fast just was not on the table.
In the combustion arena, product developers have ever more difficult goals. They must optimize fuel efficiency while meeting ever-stricter emissions standards. These can be contradictory goals (yet still call for good + fast +cheap products)! Rolf Reitz of the University of Wisconsin–Madison eloquently sums up the dilemma this way: “The grand challenge will be to devise technological advances that maximize engine efficiency, minimize pollutant emissions, and optimize tolerance to a wider variety of fuels.”
Since the easy gains have been realized, designers explore solutions that result in small, incremental gains. The consequence is that any error in simulation due to oversimplification can throw off results or cause engineers to miss innovations. Virginia Tech has an opportunity to make a significant impact on the industrial gas turbine community and, in turn, the global climate with funding from DOE. One challenge: Today’s combustor liners need to meet durability targets of 30,000 hours of use. Too high a temperature can cause liners to fail. Yet estimations of convection heat load are “most difficult to estimate accurately” due to the rapid changes that occur with the gases involved in the heat transfer process, said Virginia Tech researcher Srinath Ekkad. Advanced simulation could help answer these questions!
Combustor simulation accuracy depends on the fuel model selected. In a diesel combustion simulation using a 34 species n-heptane fuel model, severely reduced chemistry fails to predict ignition and heat release for high EGR cases (left). More-accurate chemistry is able to predict combustion and emissions performance trends when compared to actual engine measurements (right).
To that end, ANSYS has solutions that ease the dilemma of sacrificing accuracy for fast solution times. Traditionally, simulation users designing complex combustor systems had to choose between the two — calculating and processing the huge amount of data needed to describe the very complex chemical reactions. Either the simulation took a prohibitively long time to solve or oversimplifications made to speed sacrificed too much accuracy. Now we can offer intuitive yet detailed fuel models with broad and deep simulation software whose hallmark is accuracy, and best-practice methodologies to help you achieve your performance and fuel efficiency goals cost effectively and without compromising time to solution.
Our latest combustion simulation technology reduces chemistry time by orders of magnitude, virtually eliminating the bottleneck that chemistry integration produces during the simulation process. Faster time to solution means you can spend more effort exploring design alternatives, conducting experiments, understanding where and why problems occur, and explaining observations without sacrificing accuracy.
ANSYS reduces the time to simulate combustion chemistry by ~10 to 100 times to speed time to solution without sacrificing accuracy.
Since combustion simulation accuracy depends on the fuel model selected, ANSYS offers its Model Fuel Library, which includes more than 65 well validated fuel mechanisms, the outcome of a 10-year collaboration with industry, academia and national labs, so you can readily match the properties of the fuel you want to represent. This is especially important when simulating complex liquid fuels.
Because of today’s computing power, simulation engineers can represent engine geometries with amazing detail via computational fluid dynamics (CFD) meshing that approaches 100 million cells. Now you can combine high-fidelity flow simulations while predicting how the selected fuel reacts with air inside the combustor under design. ANSYS takes speed vs. accuracy out of the equation with a range of tools and methods to get the most out of both flow and chemistry. For example, ANSYS Chemkin-Pro Reaction Workbench perform automated chemistry reduction, which converts the detailed fuel model to a compute-friendly smaller size while maintaining the accuracy needed for specific engine conditions or fuel.
And, you can choose from several methods to incorporate chemistry data into the CFD solution. Each is well-suited for specific applications: direct chemistry integration coupled, table look-ups that link detailed chemical kinetics, and equivalent reactor networks that allow you to use detailed chemistry even if you don’t have specialized understanding of complex kinetics. Each leverages the depth and breadth of physics capabilities. Plus, each is based on world-class, proven technology that gives you not just any design, but the right design.
So, you can say goodbye to “Good. Fast. Cheap. Pick any two”, at least for combustion! ANSYS simulation tools eliminate the long-established trade-off of accuracy vs. speed with efficient methods and the right chemistry for your specific application.
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