Hydrostatic and nonhydrostatic simulation study on the frontal collision of buoyant plumes

Buoyant plumes from different river mouths extensively collide and converge in coastal areas worldwide, but these interactions and dynamics have not been extensively studied. Plume-to-plume interactions have been mainly investigated using hydrostatic simulations so far, which have limitations in terms of flow structure resolution. This study conducts a comprehensive investigation on both hydrostatic and nonhydrostatic simulations to understand the dynamics of the frontal collision of two buoyant plumes. The results show that nonhydrostatic simulations distinctly differ from hydrostatic simulations. Moreover, nonhydrostatic simulations yield plume evolutions that are more in line with the physical reality and field observations in terms of the flow structures. Nonhydrostatic simulations reveal bore-like structures at the rear of the plume front, clearly exhibiting their effects on the shape evolution and interfacial entrainment. Furthermore, the existing classification of plume collision is reexamined, and the basic dynamics and collision types under nonhydrostatic simulations are elucidated. Additionally, dynamic pressure characteristics are investigated, which suggests that dynamic pressure is the key to the generation and evolution of vortex structures.