Particle-scale analysis on dynamic response of turbidity currents to sediment concentration and bedforms

Abstract

The evolution of turbidity currents covers multiple physical processes, such as fluid entrainment, self-acceleration, and sediment deposition, which are associated with sediment particle behaviors and yet not well understood. This study uses a fully coupled computational fluid dynamics and discrete element method model to investigate the particle-scale dynamics of turbidity currents and their responses to different bedforms. Results show that the turbidity currents controlled by viscous drag exhibit distinct flow features, including changes in morphology, velocity evolution, and other fluid/particle kinematic indicators, depending on their initial particle volume concentration. An increase in initial particle volume concentration enhances the fluid/particle motions accompanied by generating interfacial Kelvin–Helmholtz waves. The fluid/particle indicators, with the exception of the energy loss for particle–bed collisions, have strong relevance with particle concentrations, which can be described by linear or power-law functions. Furthermore, specific bedforms play unique roles in the propagation process and deposition pattern of turbidity currents. Slope beds enhance the motion, suspension, and collision of sediment particles, and cause wave-shaped sediment deposits along the slope particularly in the high-concentration case. By comparison, weakening of particle migration on obstructed and wavy beds is accentuated by blocking effects, mainly resulting from the convex bed morphology. However, the continuously convex and concave features diminish the blocking effect of wavy beds by intensifying particle motions along the lee sides of wave-shaped bumps. The particle-scale dynamics of turbidity currents is linked to the relative sizes of the underlying bedforms, which should be noted and further studied in our future work.