Monami dynamics and instability dependence on Reynolds number and seagrass buoyancy

The interaction between flow and submerged seagrass beds can generate instabilities that evolve into vortices, induce grass blade oscillations, and affect the transport of sediment and nutrients in aquatic systems. We develop a numerical two-phase model to simulate the unstable flow through a seagrass bed. The seagrass is modeled as buoyant blades that do not resist shear and deform to adjust instantaneously to the fluid drag. The shape of the grass blades at all times can therefore be directly computed from the velocity field, and the flow within the seagrass bed responds to the drag, which depends on the shape of the blades. We study the instability onset with respect to a steady state as a function of grass buoyancy, which dictates deformability in the model, and Reynolds number. We then visualize how the vortices induce a collective waving motion in the seagrass bed, known as monami, and the vortex-driven material exchange resulting from this interaction.