Numerical Investigation of the Role of Particle Settling Velocity in Turbidity Currents

Resumo

Turbidity currents are sediment-laden gravity flows that travel along the seafloor, driven by the excess density of suspended particles. They play a central role in shaping submarine landscapes and transporting sediment into the deep ocean, with significant implications for geology, ecology, and offshore oil prospecting. The dynamics of these flows depend critically on the interaction between turbulence, sediment suspension, and particle settling. This study investigates the role of particle settling velocity in modulating the structure and evolution of turbidity currents using direct numerical simulations (DNS) with approximately 100 million grid points and large eddy simulations (LES) of spatially evolving currents in extended domains (up to 1500 times the inlet height), solved via the spectral element method using the open-source solver Nek5000. We analyze a wide range of settling velocities on a shallow slope to isolate its impact on key flow properties such as velocity, concentration profiles, turbulent mixing, and entrainment. The results show that for sufficiently low values the flow behaves like a subcritical current. However, higher settling velocities lead to near-bed stratification and flow instabilities that manifest as internal hydraulic jumps with cyclic transitions between subcritical and supercritical regimes. For sufficiently high settling velocities, the flow permanently transitions to a supercritical state marked by persistent interfacial turbulence. The findings highlight the importance of settling velocity not only in controlling sediment deposition but also in governing the internal turbulence structure and entrainment of turbidity currents.