Intellectual Merit:
Developing an understanding of the complex interaction of fluid dynamics and chemical reactions in practical combustion devices is of fundamental importance for the development of combustion systems. Achieving this goal will assist in the development of the tools required for predictive modeling of such systems. For modeling to be reliable, systematic validation with an extensive experimental database is indispensable - a task for which practical, and inevitably complex, configurations are not as well suited as simple, well-defined laboratory flames. The PIs propose highly turbulent counterflow flames (TCFs) as a benchmark configuration for this type of systematic experimentation and modeling. They offer significant advantages, such as: flame stabilization without a pilot at high Reynolds numbers; compactness, with significant advantages for highly resolved computations; and versatility, with the ability to access a broad range of combustion regimes, especially those of industrial relevance.
This research is collaboration between Yale and Cornell with further collaboration with Sandia National Labs. A series of experiments on TCFs, operating in both non-premixed and premixed modes, will be performed at Yale and at Sandia; simultaneously at Cornell, the same flames will be tackled computationally using the PDF and the LES-PDF methodologies. The principal contributions made by this research will be: (i) Providing qualitative understanding and quantitative data of TCFs in important but little-explored combustion regimes; (ii) Determining and demonstrating the capabilities of the PDF and LES-PDF methods to model accurately the TCFs in different regimes, and improving the sub-models as necessary. (iii) Providing the understanding and data necessary for TCFs to be a valuable benchmark for the development and testing of turbulent combustion models.
Broader Impact:
Understanding turbulent combustion is important for power generation and propulsion. It is also important for environmental pollution and compliance with regulatory restrictions. The proposed activity will provide a high quality database, including well characterized boundary conditions. This will be made available on the web to the combustion community for further modeling within the framework of ongoing international collaborations, such as the Sandia-sponsored Turbulent Nonpremixed Flames Workshop.
The proposed research will be accompanied with teaching and outreach activities. The PI at Yale has advised female students, award winning graduate students and high school students. He has also trained local schoolteachers in the development of K-12 curricular units focused on energy. He will continue to pursue these activities and integrate them with the project. The Cornell PI has a good track record of recruiting women Ph.D. students and transferring the fruits of his research to industry. Undergraduate students will be exposed to experimentally simple projects, such as flow visualization and phenomenological evidence of various burning regimes.
Computer simulations play an important role in the design and development of new and improved combustion technologies for power generation, transportation and other applications. The goals are to increase efficiency, decrease emissions, facilitate the use of biofuels, and enable carbon capture and sequestration. This project aimed at developing, demonstrating and testing an advanced modeling approach used in the simulation of turbulent combustion. The methodology used in this project combines the techniques of large-eddy simulation to represent the three-dimensional, unsteady turbulent flow, and the probability density function approach for handling the complex interactions between the turbulence and the hydrocarbon chemistry. The particular test case considered is the counterflow burner in which a turbulent flame if formed between opposing jets of reactants and combustion products. In order to test the accuracy of the methodology, companion experiments have been performed at Yale University and Sandia National Labs. A major part of the research performed has been the development of the computer codes implementing the approach, and this has been completed successfully. Calculations have been performed and compared with the experimental data. These comparisons show that the method is quite successful in accounting for the principal experimental observations. The research is ongoing, with more detailed comparisons being made with the experimental results over a broader range of conditions, to more fully assess the capabilities of the methodology. This research represents an important step towards applying to the design of improved combustion equipment the combined methodology of large-eddy simulation and the probability density function approach.
