Flapping dynamics of a flexible propulsor near ground.*

The flapping motion of a flexible propulsor near the ground was simulated using the immersed boundary method. The hydrodynamic benefits of the propulsor near the ground were explored by varying the heaving frequency ($St)$ of the leading edge of the flexible propulsor. The propulsion near the ground had some advantages to generate thrust and propel faster than that away from the ground. The mode analysis and the flapping amplitude along the Lagrangian coordinate were examined to analyze the kinematics as a function of the ground proximity ($d)$ and the heaving frequency ($St)$. The trailing edge amplitude ($a_{tail} )$ and the net thrust ($\bar{{F}}_{x} )$ were influenced by the heaving frequency ($St)$ of the flexible propulsor. The hydrodynamic benefits of the flexible propulsor by the ground effect were discussed within the framework of dynamics and kinematics. The trailing edge amplitude presented the high-peak and the low-peak. Each peak showed distinct difference in terms of both the dynamics and the kinematics. The vortical structures in the wake were analyzed for different flapping conditions.