Esc. Ching et al., EFFECTS OF A LARGE-SCALE MEAN CIRCULATING FLOW ON PASSIVE SCALAR STATISTICS IN A MODEL OF RANDOM ADVECTION, Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics, 58(2), 1998, pp. 1948-1954
We study the effects of a large-scale mean circulating flow on passive
scalar statistics in turbulent advection using a two-dimensional latt
ice model. The incompressible advecting velocity field consists of a l
arge-scale circulation plus fluctuations. The latter are modeled by a
random Gaussian field that has a finite correlation time but is statis
tically independent at different lattice points. In the presence of th
e large-scale flow, we find that the profiles of both the mean and the
rms fluctuation of the passive scalar are modified significantly, and
have close resemblance to those observed experimentally in turbulent
convection. The one-point probability density functions (PDFs) of the
passive scalar at the two sides are affected by the large-scale flow a
nd become more skewed. There is, however, not much change for the PDFs
at other locations. Furthermore, the shape of the PDFs of the scalar
increments remains the same with or without the presence of the large-
scale flow, supporting the idea that large-scale effects can be filter
ed out by studying increments.