Effect of viscous-convective subrange on passive scalar statistics at high Reynolds number

Abstract

In modeling turbulent mixing at high Reynolds number (Re), the small-scale statistics of a passive scalar are assumed similar to those of the velocity. Research shows this to be invalid at either high Re or high Schmidt number individually. We hypothesize that both inertial-convective and viscous-convective subranges are needed for sufficient scale separation in both velocity and scalar fields, such that small-scale statistics of the scalar approach those of the velocity. We explore this using direct numerical simulations of up to ${14256}^{3}$ and find that at high Taylor Reynolds number of 633, similarity may be assumed between velocity and scalar statistics for mixing in water, but not in air.