Accuracy of Scalar PDF Method for Turbulent Nonpremixed Combustion (Evaluation of Reynolds Stress Model)

The accuracy of a scalar probability density function method, which is able to deal with reaction exactly, has been investigated in terms of a second order closure model for flow field evaluation. Numerical calculations have been conducted in the configuration of a hydrogen/nitrogen jet nonpremixed flame. The second order closure model is based on a Reynolds stress model. The present solution is a combined PDF/moment method, in which PDFs are evolved to match both the means and variances of mixture fraction from both the PDF and moment methods. Then the two moment equations of mixture fraction are based on the second order closure. The present evaluation is based on a comparative study with the first order closure model based on a k-ε 2 equation model. The present scalar PDF model with the second order closure model evaluates adequately anisotropy and then the anisotropy affects strongly the mixing process in the near field. The spread of the jet flame is able to be evaluated adequately by the second order closure model than by the first order one. The early flow filed is extremely important and the present initial low turbulences affect the downstream flame structure.