Numerical Investigation on Hydrodynamic Performance of Flapping Plates with Non-Uniform Spanwise Flexibility Using Fluid Structure Interaction

摘要

Fluid structure interactions (FSI) in biological propulsions are commonly observed in nature. For example, fish caudal fins and cetacean flukes. It is commonly believed the flexibility of the propulsors helps with the thrust producing and improves the swimming efficiency. However, the effects of non-uniform spanwise flexibility on the hydrodynamic performance of flexible propulsors are still elusive. In this paper, a strong coupling FSI solver was developed to study the hydrodynamic performance of flexible flapping plates with nonuniform spanwise flexibility. The flow field was computed using an in-house immersed boundary method (IBM) based direct numerical simulation (DNS) solver, and the structural dynamics was solved using an open source FEM code. The FSI solver was validated against the experimental data of a flexible flapping plate. The FSI solver was then used to simulate square flapping plates with different non-uniform distributions of spanwise flexibility that was achieved by changing the thickness ratio, τ, between the center and the tip of the plate. It was found non-uniform spanwise flexibility has a significant impact on the hydrodynamic performance of the plates. Specifically, the mean thrust increased with an increasing thickness ratio within the chosen range of τ between τ = 1 and 7. The hydrodynamic power consumption reached its minimum value and the propulsive efficiency reached its maximum value at τ = 3.