Abstract: Suspended load movement is an important form of river sediment transport, and its existence in the flow poses a significant impact on flow turbulences. The movement is complicated, and no agreement has been reached on the mechanism of water-sediment interaction. This paper presents an application of the OpenFOAM two-phase flow model and its simulations of equilibrium sediment transport under different flow conditions, focusing on how the size, density and concentration of suspended sediment particles impact turbulent flow characteristics, and on the mechanism of flow turbulences modulated by drag force, density gradient, and particle collision. The results show that 1) with an increasing suspended particle size, the velocity of both the water flow and particles decreases overall, and the velocity gradient near the riverbed increases significantly; In the near-wall layer, sediment concentration gradient increase, turbulence intensity decreases first and then increases, and its peak values increase. 2) An increase in suspended particle density leads to an increase in the average turbulent flow velocity. The smaller the suspended particle density is, the more uniform the vertical concentration profile, and vice versa. 3) An sediment concentration increase reduces the average turbulent flow velocity and turbulence intensity, and the higher the concentration, the more obvious its suppressing effect. 4) An increase in drag force raises turbulent flow rate and suppresses turbulence intensity and sediment suspension. Suspended sediment density gradient has a suppressing effect on both bottom layer velocity and top layer turbulence intensity. Particle collision reduces average velocity and significantly enhances turbulence, thus promoting sediment suspension.

Key words: two-phase flow, suspended sediment, turbulence modulation, drag force, particle collision, density gradient