Along-slope bottom currents and down-slope (gravity-driven) turbidity currents coexist in the ocean and interact during their flow processes. The interaction between turbidity currents and bottom currents plays a crucial role in determining the lateral stacking of sediments and the direction of channel migration. Currently, there is ongoing debate regarding the migration direction, with two primary contrasting views: upstream migration versus downstream migration relative to the bottom current. However, due to the challenges in directly observing unidirectionally migrating channels in nature, the sedimentary hydrodynamics and underlying flow mechanisms remain poorly understood. In this study, we employ numerical simulations to systematically analyze the internal flow characteristics and depositional patterns within channels subjected to varying degrees of confinement. Our results demonstrate that variations in channel confinement influence the intensity of the interaction and the nature of the secondary flow, ultimately determining the spatial distribution of sediments. As confinement decreases, the migration pattern of a channel changes from negligible migration to migration in the downstream direction of the bottom current. Subsequently, it changes to migration in the upstream direction of the bottom current. This research provides a novel theoretical perspective for understanding the diametrically opposite migration directions of unidirectionally migrating channels and insights into the turbidity–bottom current interaction processes and the evolutionary mechanisms of deep-sea depositional geomorphology.

Submarine channels are critical conduits for sediment transport by turbidity currents, yet the quantitative influence of channel geometry on flow dynamics and sediment segregation remains poorly understood. Based on computational fluid dynamics, we constructed six three-dimensional numerical models of submarine channels with varying curvatures (R1–R3) and axial slopes (R4–R6) using ANSYS Fluent 17.2, with model settings informed by seafloor morphology from the South China Sea. The Eulerian–Eulerian multiphase model coupled with the standard k-ε turbulence model was used to simulate density fields, velocity structures, and sediment distributions. Results show that low-curvature channels exhibit symmetric density evolution and uniform sediment distribution, whereas high curvature induces pronounced asymmetry with a steep outer-bank density front and triggers secondary flow reversal. Increasing curvature also enhances flow thickness and radial mass flux. Increasing axial slope markedly elevates downstream velocity (0.09 to 0.16 m/s), reduces flow thickness, and shifts sediment distribution toward the inner bank without inducing secondary flow reversal. This study provides a parametric comparison of curvature versus slope effects on turbidity current dynamics and sedimentation patterns under fixed-bed, rectangular-channel assumptions. The findings offer a qualitative reference for interpreting sedimentary architectures in deep-water systems such as those in the South China Sea and analogous rift basins. Results are hypothesis-generating, pending further validation with field data and morphodynamic modeling.