Statistics of a passive scalar in homogeneous turbulence

Statistics of a passive scalar with Sc=1 transported by steady homogeneous turbulence at R-lambda=427 and P-lambda=427 is studied by using high-resolution direct numerical simulation. The Obukhov-Corrsin constant of the three-dimensional scalar spectrum in the inertial-convective range is found to be 0.68+/-0.04. It is proved that the 4/3-law for the scalar-velocity triple correlation holds in both inertial-convective and viscous-convective ranges when Sc>1, and found that the 4/3-law is approached with increase in Peclet number. Structure functions of the passive scalar increment and their local scaling exponents are computed as functions of the separation distance, and it is found that there exist two scaling ranges: the inertial-convective range and a narrow precursory range to the viscous-convective range. The scaling exponents in the inertial-convective range are found to be smaller than those of the velocity field and do not saturate, whereas they saturate at about 1.5 in the short precursory range to the viscous-convective range. It is also found that, contrary to the scalar case, the mixed scalar velocity structure function has a well-developed single scaling range. The scalar and scalar dissipation fields are visualized and compared with the kinetic energy dissipation field. The scalar field has a particular shape with a large-scale plateau, sharp cliff and deep valley, a mesa-canyon structure.