Details

Autor(en) / Beteiligte

• Haddadian, S.
• Ozdemir, C. E.
• Goodlow, B. L.
• Xue, G.
• Bentley, S. J.

Titel

Direct Numerical Simulations of Miniature Along‐Shelf Current‐Supported Turbidity Currents: Conceptual Investigation of Velocity Structure and Drag Coefficient

Ist Teil von

• Journal of geophysical research. Oceans, 2021-08, Vol.126 (8), p.n/a

Ort / Verlag

Washington: Blackwell Publishing Ltd

Erscheinungsjahr

2021

Quelle

Wiley-Blackwell Journals

Beschreibungen/Notizen

• Alongshore current‐supported turbidity currents (ACSTCs) are a subclass of wave‐ and current‐supported turbidity currents. They are one of the agents responsible for the dispersal of the river‐borne sediments on the continental shelf, which constitutes a major phenomenon controlling the geomorphic evolution of ocean‐basin margins over geological time. Therefore, parameterization of the sediment flux associated with ACSTCs will help its implementation in operational models and quantify the sediment flux budgets on the continental shelf. The velocity structure of ACSTCs and the amount of sediments suspended by them are crucial to determine the suspended sediment flux. This study investigates the velocity structure of a simplified miniature ACSTC over an erodible bed composed of fine sediments. Direct numerical simulations are conducted for various bed erosion parameters and sediment settling velocity. The role of sediment‐induced stable density stratification on the velocity structure of ACSTCs is analyzed. The simulation results indicate that density stratification and the drag coefficient are functions of the product of sediment settling velocity and sediment concentration. The velocity profile was found to deviate toward the alongshore direction with strengthening density stratification, which enhances the drag coefficient. By using the Monin‐Obukhov theory, the drag coefficient associated with the cross‐shelf propagation of ACSTCs is formulated as a function of the Reynolds number, sediment concentration, and sediment settling velocity. Plain Language Summary One of the mechanisms that are responsible for sediment emplacement on the continental shelf is the slow‐motion of sediment suspended in seawater driven by currents parallel to the shore known as alongshore current‐supported turbidity currents (ACSTCs). One of the poorly understood aspects of ACSTCs is their velocity profile, which is central to quantifying the amount of sediments carried by them. This is especially important because of its ramifications to the global budgets of geochemically important particulate matter. This paper investigates the velocity profiles of ACSTCs by conducting fine‐scale numerical simulations and provides relations for their parameterization. Key Points Direct numerical simulations were conducted for alongshore current‐supported turbidity currents over an erodible fine sediment bed for various critical shear stress for erosion and sediment settling velocity The role of density stratification in modulating the velocity profile and the drag coefficient was analyzed by using the Monin‐Obukhov theory, and it was found that the Monin‐Obukhov theory can be used to estimate the modulation in the velocity profile By using the Monin‐Obukhov theory and quantifying the directional variation of the mean velocity vector a drag coefficient as a function of the settling velocity and sediment concentration is proposed