Implementation of a conditional moment closure for mixing sensitive reactions

摘要

An implementation of the conditional moment closure (CMC) of Bilger (Phy. Fluids A 5 (1993) 436) and Klimenko (Fluid Dyn. 25 (1990) 327) has been carried out in the commercial CFD software FLUENT. A new implementation method is suggested that uses the CMC-equations to calculate an unconditional reaction rate that is subsequently inserted in a Reynolds averaged species equation. The objectives are to ensure conservation of reacting species by elimination of the spurious term that usually contaminates a CMC solution and to obtain convergence on a coarser grid than is usually required in CMC. The implementation has been successfully carried out for two sets of well-known mixing sensitive reaction pairs (parallel competitive and competitive consecutive) that both have one instantaneous and one fast irreversible reaction. Calculations with different discretizations of the CMC-equations in mixture fraction space have been performed and compared to experiments, full/finite-mode PDF models and the interpolation model of Baldyga. It is shown that the suggested implementation can achieve sufficient numerical accuracy with a much coarser mixture fraction space discretization than standard CMC implementations, which allows for more efficient CFD calculations. (C) 2004 Elsevier Ltd. All rights reserved.