PERTURBATION SCHEMES FOR FLOW IN RANDOM-MEDIA

We utilize a many-body style formalism to compute the long-range effec tive diffusivity kappa(e), for dispersal of a passive scalar field in a random irrotational flow with molecular diffusivity. By comparing th e theoretical results with the outcome of computer simulations we show that a renormalization-group approach that includes an appropriate ve rtex renormalization is superior to low-order perturbation theory and to the Hartree-Fock approximation, and gives a rather accurate method of computing kappa(e) for a range of parameter values.