Forward and backward multi-particle dispersion in homogeneous isotropic turbulence

Abstract

Turbulent diffusion in homogeneous isotropic turbulence is numerically investigated using the direct numerical simulation (DNS). The four-dimensional turbulence database allows us to track fluid particles not only in the forward direction of time but also in the backward direction. Two-particle dispersion has been studied in previous studies and it is known that backward diffusion is faster than forward diffusion. However, little is known about multi-particle dispersion due to the difficulty of observing it experimentally. Studies on backward diffusion are also limited. In this study, multi-particle dispersion is numerically investigated and its properties are discussed, e.g., direction of time and geometry of a tetrahedron. The results show that forward and backward diffusions of multi-particles behave differently at the beginning and evolve similarly after the transient time, but the coefficients of the backward direction are larger than those of the forward direction.

Keywords

• direct numerical simulation
• particle tracking
• turbulent diffusion
• multi-particle dispersion
• tetrahedron