A multi-scale turbulent dispersion model for dilute flows with suspended sediment

• A turbulent dispersion model is proposed for large-scale two-phase flow problems.
• Schmidt number is modeled by two Stokes numbers describing different eddy sizes.
• The model is suitable for dilute flows with a wide range of Stokes numbers.

Turbulent dispersion causes sediment particles to be transported from high concentration regions to low concentration regions and determines the concentration distribution of suspended sediment. In this study, a new turbulent dispersion model is proposed for large-scale flows with suspended sediment. Two Stokes numbers are used to describe the turbulent dispersion through the Schmidt number: (1) st≡τp/τfst≡τp/τf, where τpτp is the particle response time and τfτf the fluid turbulence time scale, and (2) stη≡τp/τηstη≡τp/τη, where τητη is the Kolmogorov time scale. The former is used to account for interaction between large eddies and sediment particles, while the latter for small eddies. The new turbulent dispersion model is validated against experimental data available for open channel flows under a wide range of conditions for dilute flows  : the volume concentration of suspended sediment could vary from 10-610-6 to 0.080.08, stst could vary from 2×10-32×10-3 to 8 and stηstη could vary from 2×10-22×10-2 to 60.