A MAPPING CLOSURE FOR TURBULENT SCALAR MIXING USING A TIME-EVOLVING REFERENCE FIELD

A methodology for modeling passive scalar mixing in homogeneous turbulence using a new mapping closure approach is developed. The physical scalar field phi(y,t) (y-space coordinate, t time) is mapped using a mapping function, X(t), onto a reference scalar field theta(y,t), whose evolution is known. There are two main differences between the present approach and that of Chen et al. [Phys. Rev. Lett. 63, 2657 (1989)]. In the present approach, the reference field is time evolving and not restricted to a Gaussian. The evolution equation of the mapping function is derived for a general reference field. Gaussian and beta-pdf reference fields are investigated. Calculations from both reference fields are compared with the heat conduction simulation (HCS) data of Girimaji (NASA Contract. Rep. 4446, 1992). The limits of validity of the mapping closure approach are discussed.