Application of the elliptic conditional moment closure model to a two-dimensional nonpremixed methanol bluff-body flame

Abstract

A turbulent nonpremixed flame of methanol stabilized on a bluff body is simulated by the conditional moment closure (CMC) model. Full spatial variation of the conditional quantities is taken into account for the elliptic flow field. Comparison has shown good agreement for the conditional averages of the temperature and major species concentrations. Overprediction of OH near the stoichiometric mixture fraction is attributed to inaccurate prediction of the conditional scalar dissipation rate. Discrepancy for CO and H-2 may be due to several possible reasons such as the chemical kinetic mechanism or differential diffusion, although not clear yet. The results of the CMC model are in better agreement with conditional measurements than those of the stationary laminar flamelet model (SLFM), which is a quasi-steady form of the CMC without the convection term. The measurement data and CMC results are also in qualitative agreement for minor radial dependence of the conditional intermediate species concentrations. There is almost no noticeable difference in the unconditional Favre mean predictions by the CMC and SLFM. Discrepancy between prediction and measurement for the unconditional Favre average is due to inaccurate prediction of the pdf and mixing field by the k-epsilon turbulence model. (C) 1999 by The Combustion Institute.