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Self-propulsion of a flapping flexible plate near the ground.

The self-propulsion of a three-dimensional flapping flexible plate near the ground is studied using an immersed boundary-lattice Boltzmann method for fluid flow and a finite-element method for plate motion. When the leading edge of the flexible plate is forced into a vertical oscillation near the ground, the entire plate moves freely due to the fluid-structure interaction. The mechanisms underlying the dynamics of the plate near the ground are elucidated. Based on the propulsive behaviors of the flapping plate, three distinct regimes due to the ground effect can be qualitatively identified. These regimes can be described briefly as the expensive, benefited, and uninfluenced propulsion regimes. The analysis of unsteady dynamics and plate deformation indicates that the ground effect becomes weaker for a more flexible plate. We have found that a suitable degree of flexibility can improve propulsion near the ground. The vortical structure around the plate and the pressure distribution on the plate are analyzed to understand propulsive behaviors. The results obtained in this study can provide some physical insights into the propulsive mechanisms of a flapping flexible plate near the ground.