Reactive mixing, closure models

The most difficult term to close in (7.73) is the reaction rate terms denoted by Sc uj). To simulate turbulent reactive flows accurate modeling of this term is very important. For slow reactions (i.e., Dai 1) the turbulent mixing is completed before the reaction can take place thus an adequate closure is available ... 

Donaldson, C. (1975). On the modeling of the scalar correlations necessary to construct a second-order closure description of turbulent reacting flows, in Turbulent Mixing in Nonreactive and Reactive Flows, S. N. B. Murthy, ed.. Plenum Press, New York, pp. 131-162. 

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