An evaluation of the assumed beta probability density function subgrid-scale model for large eddy simulation of nonpremixed, turbulent combustion with heat release

The assumed beta distribution model for the subgrid-scale probability densi ty function (PDF) of the mixture fraction in large eddy simulation of nonpr emixed, turbulent combustion is tested, a priori, for a reacting jet having significant heat release (density ratio of 5). The assumed beta distributi on is tested as a model for both the subgrid-scale PDF and the subgrid-scal e Favre PDF of the mixture fraction. The beta model is successful in approx imating both types of PDF but is slightly more accurate in approximating th e normal (non-Favre) PDF. To estimate the subgrid-scale variance of mixture fraction, which is required by the beta model, both a scale similarity mod el and a dynamic model are used. Predictions using the dynamic model are fo und to be more accurate. The beta model is used to predict the filtered val ue of a function chosen to resemble the reaction rate. When no model is use d, errors in the predicted value are of the same order as the actual value. The beta model is found to reduce this error by about a factor of two, pro viding a significant improvement. (C) 2000 American Institute of Physics. [ S1070-6631(00)50310-9].