Impact of Turbulence Energy Cascade Process and Eddy Intermittency on Suspended Sediment Particle in Open Channel Flow

Turbulence is chaotic and full of different spatial and temporal scales of eddies in its energy cascade process (Richardson, 1922). Moreover, it is observed that erratic behavior occurs in turbulent properties, such as flow velocity (Townsend, 1949) might result in the intermittency of turbulent eddy occurrences. As we know, the movement of sediment particles is not only influenced by flow advection but also by turbulent eddies. For turbulence, particle diffusivity is a coefficient used to measure the impact of turbulence on particles. This study attempts to build a linkage between turbulent eddies and particle diffusivity. On the other hand, turbulent eddies are an intermittent process, which will be further considered in this study.

 

To consider the chaotic property of turbulence on particle motion, Man and Tsai (2007) proposed the stochastic diffusion particle tracking model (SD-PTM) based on the mass conservation and the Langevin equation of particle displacement to simulate the suspended particle in open channel flow. Their model regards suspended particle movements as a stochastic process and uses Brownian motion to describe particle irregular trajectories caused by turbulence. To investigate the impact of the energy cascade process and eddy intermittency on particles, we aim to develop a modified stochastic diffusion particle tracking model (MSD-PTM) that incorporates the effect of the energy cascade process and turbulent intermittency. In the proposed model, an additional stochastic term will be considered to simulate the impact of the turbulence energy cascade process. In addition, a physical parameter will be used to represent the intermittency effect of eddies. The MSD-PTM will be compared with SD-PTM for statistical properties of particle movement such as the ensemble statistics of particle trajectory and concentration profile. The sensitive analysis will be used to evaluate the degree of impact of the turbulent energy cascade and eddy intermittency on suspended sediment particles.