Investigation of Reactive Scalar Mixing in Transported PDF Simulations of Turbulent Premixed Methane-Air Bunsen Flames
Transported probability density function (TPDF) simulations have been performed in conjunction with DNS data to investigate the mixing characteristics of reactive scalars in two turbulent lean premixed methane-air Bunsen flames with Case A being close to the corrugated flamelet regime and Case C being close to the broken reaction zones regime. The study shows that with an accurate mixing timescale of progress variable being provided, TPDF simulations using the EMST mixing model predict scalar mixing and flame characteristics reasonably well. Modeling reactive scalar mixing rate remains one key challenge. For turbulent flames close to the flamelet regime, i.e. Case A, the turbulent flame structure represented by the scatter of OH, as well as the resemblance of the flame induced dissipation rate to the actual dissipation rate, highlights the necessity to account for flame structure when modeling reactive scalar mixing in flamelet region. A posteriori tests show that the hybrid mixing timescale model, which accounts for both turbulence and flame structure effects on the scalar mixing timescale, yields better performance than the constant mechanical-to-scalar timescale model for turbulent premixed flames close to the flamelet regime. Moreover, the hybrid model shows potential for modeling differential mixing rates of intermediate species featuring their own characteristic timescales. The effects of progress variable definition and turbulence modeling on the computed flame characteristics are investigated, and the significance of turbulence modeling in RANS-TPDF simulation is illustrated.
KeywordsTurbulent premixed flames Reactive scalar mixing Transported PDF methods Mixing models
The work at Tsinghua is supported by National Natural Science Foundation of China 91841302 and 51476087. Simulations are performed with the computational resources of the Tsinghua National Laboratory for Information Science and Technology. The work at Sandia is supported by the Division of Chemical Sciences, Geosciences and Biosciences, the Office of Basic Energy Sciences, the US Department of Energy (DOE). Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA-0003525.
Compliance with Ethical Standards
Conflict of Interests
The authors declare that they have no conflict of interest.
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