| Summary: | Conditional source-term estimation with laminar flamelet decomposition has
been utilized to model the mean chemical source term in a predictive RANS
simulation of two different problems. With this model, integral equations
relating the unconditional mean temperature and species fields to the conditional
means are used to determine the flame structure as a combination of
basis functions formed from solutions to the unsteady laminar flamelet equations.
In the simulation of the Sandia Flame 'D', a well studied co-flowing
piloted jet flame with a steady average solution, a converged solution was
obtained which captured the trends in the temperature and major species,
although the nitric oxide prediction overestimated the peak concentration by
a substantial margin. Simulation of the autoignition process of non-premixed
methane produced simulation predictions in excellent agreement with the experimental
data. Using a new, more stringent, criteria to define ignition than
earlier studies, the effect of ambient temperature on the ignition delay was
captured, as was the expected physical behaviour prior to ignition. The errors
in the simulation of the co-flowing piloted jet can be attributed to a large
degree to the lack of ability of the basis functions used to account for the
effect of the pilot flame. That the autoignition simulation was much more
successful highlights the importance of including all relevant physics in the
library of basis functions. Earlier formulations of the model were extended
by expanding the sample space for the basis functions to include a wide variety
of solutions to the laminar flamelet equations; in order to distinguish
between the larger set, a new method of stabilizing the numerics was found
to be necessary and the number of scalars used to determine the flame structure
was increased. The formulation is easily extensible to libraries of basis
functions which are capable of including effects such as pilot and edge flames
not captured by the laminar flamelet solutions.
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