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Are You Getting the Value You Expect From Combustion Simulation?
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Are You Getting the Value You Expect From Combustion Simulation?

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Today’s business and regulatory environment requires managers to evaluate how they are investing in future technologies to achieve compliance and productivity goals. Taking advantage of opportunities …

Today’s business and regulatory environment requires managers to evaluate how they are investing in future technologies to achieve compliance and productivity goals. Taking advantage of opportunities in the market requires the identification of new methods of doing business that provide revolutionary improvements in design cost, time-to-market, and product performance. This whitepaper focuses on an area that has proven in the past to provide revolutionary advantage – combustion simulation.

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  • 1. A WHITE PAPER BY REACTION DESIGN<br />ARE YOU GETTING THE VALUE YOU EXPECT FROM COMBUSTION SIMULATION?<br />Today’s business and regulatory environment requires managers to evaluate how they are investing in future technologies to achieve compliance and productivity goals. There are signs of global economic recovery and new growth areas are beginning to surface. Of course, these new growth areas present design challenges in the form of lower emissions guarantees, increased fuel flexibility for non-standard fuels, improved operational flexibility and lower cost. <br />Taking advantage of opportunities in the market requires the identification of new methods of doing business that provide revolutionary improvements in design cost, time-to-market, and product performance. This series of whitepapers focuses on an area that has proven in the past to provide revolutionary advantage – combustion simulation. Over the past 10 years, Computational Fluid Dynamics (CFD) codes have become the exclusive combustion simulation tools employed by gas turbine and burner manufacturers. But, today, with orders of magnitude improvement in computing power and large investments in people and software licenses, are we where we need to be?<br />Is combustion CFD delivering on its promises?<br />The early promise of CFD-based design approaches was that the predictable nature of the calculations would help allow for studies of multiple combustor designs prior to prototyping. As part of the development flow, the promise was that simulation could predict important system attributes such as stability and emissions performance thereby reducing the need for costly experimental testing. While it appears that results vary widely among organizations, most managers are:<br />
    • Receiving ever increasing requests for computer hardware and software licenses to feed larger, more complex combustion CFD simulations with little tangible evidence of truly predictive results
    • 2. Spending more than ever before on experimental testing and test facilities are increasingly overbooked
    • 3. Recognizing that proposed improvements in CFD accuracy that promise better capture of the physics are too expensive to implement. (E.g. turbulence models such as LES, increased mesh sizes, improved atomization models, etc.)
    Why aren’t alternate approaches to CFD been investigated? Perhaps it is a sign of the times but most middle-level technical managers have a risk adverse mindset after having survived layoffs and budget cutbacks. They are happy to have jobs and don’t want to risk their credibility by looking at potentially disruptive alternatives. In today’s business environment the installation of a modern design methodology and computational environment that is both predictive and cost effective has become a necessity.<br />Growth of the role of combustion simulation in the development of gas turbine combustors and burners has been revolutionary over the last 30 years. Now, virtually every combustion equipment manufacturer uses CFD in their designs. This approach worked well-enough when we were simply looking to get the flame temperatures down to reduce NOx. But, now that we’ve successfully developed ultra-low NOx combustion equipment, we are facing a completely new set of challenges that cannot be addressed by CFD. Because of our early successes, we have become increasing more reliant on combustion CFD to help solve our design challenges over the decade. While it served us well in the past, increased investment in CFD is no longer yielding solutions to our key combustion design problems. For all of the things that CFD can do well; it cannot handle anything more than the most simplistic representation of fuel composition and kinetic effects. Today’s combustion challenges such as Lean Blow Off (LBO), ignition, flashback, fuel flexibility and emissions are all dominated by fuel kinetics. Regardless of how well you capture the physics, you don’t have a chance of solving modern combustion problems without adequate fuel kinetics.<br />How did we get here?<br />The application of combustion CFD really started in the 1970’s with some forward thinking organizations investing in in-house developed CFD codes. During the 1980’s, these codes were upgraded to accept realistic hardware geometries. More advanced combustion and turbulence models and the emergence of viable commercial CFD software allowed the widespread adoption of CFD in the combustion market during the 1990’s. The inherent chemistry limitations of CFD were not a problem at the time because the focus was on achieving low NOx solutions by lowering the flame temperature through combustion staging (i.e. lean or rich combustion). We did not look to CFD for NOx prediction. We simply needed to predict the temperature to identify low flame temperature designs that would produce less NOx. Simple chemistry in CFD was good enough for the job at the time.<br />Today’s engineers are taught how to design almost exclusively using CFD simulation. Engineering students typically have little or no experience in experimental combustion. Since they are used to solving problems with CFD, they tend to treat it as their only tool. This is in stark contrast to the typical combustion engineering student of the 1970’s and 80’s where a combination of experimental and numerical techniques were part of the curriculum. Compounding the problem is that most of the senior engineers with experimental expertise are leaving the workforce. <br />Why look for an alternative approach?<br />Because our current set of software tools and methodologies is not aligning with our productivity and cost containment goals. In upcoming pieces of this Series, we will present the success some organizations have had by employing alternate combustion simulation techniques that extend their existing CFD infrastructure but provides new levels of predictive accuracy while holding the line on compute resource requirements. We will discuss how many years of advanced research in combustion and fuel chemistry has led industry experts to the conclusion that more CFD and more computers coupled with simplistic kinetic representations simply cannot produce reliable results. We will detail how an advanced technique can be used to provide the kind of accuracy in emissions and combustion performance that can actually eliminate the need for some experimental tests. Specifically, we will show how these techniques can minimize the need to exhaustively test all of the fuel and operating condition combinations for your designs. Leaders in combustion design are achieving are shorter development schedules, improved design quality going into and out of experimental test programs and more accurate predictions of combustion performance that help minimize the risk of post-sale field issues.<br />

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