Quasi-steady modeling of turbulent nonpremixed combustion

In turbulent reacting flows of practical interest, the application of mixtu re fraction based combustion models is computationally burdensome due to th e added dimension of the mixture fraction. (The term "mixture fraction base d combustion model" refers to an approach that uses the mixture fraction as an independent variable.) Recently, Buriko et al. [1] have suggested that the quasi-steady approximation in mixture fraction based modeling is applic able to predict average species mass fractions in turbulent hydrogen/air je t flames. This holds potentially great advantages in treating more general, nonpremixed, reacting Rows which may be computationally intractable withou t resorting to quasi-steady modeling. This paper extends the quasi-steady m odeling investigation of [1] to conditionally averaged quantities. The vali dity condition for quasi-steady (mixture fraction based) modeling is derive d and discussed. As practical illustration, the condition is applied to the turbulent hydrogen/air jet diffusion flames of Barlow and Carter [2-4]. (C ) 2000 by The Combustion Institute.