CFSI Study on Effect of Structural Flexibility of a Pitching Hydrofoil in a Free-stream Flow

Computational Fluid-Structure Interaction (CFSI) study is presented for the effect of structural stiffness of a flexible hydrofoil on hydrodynamics characteristics and propulsive performance of the pitching foil in a free stream flow. Using a level-set and immersed-boundary based hybrid finite volume element method (LSIB-HFVEM), in-house code based 2D simulations are done for various stiffness and Strouhal number at a constant Reynolds number Re = 5000. Unified CFSI analysis is presented by considering a time-wise synchronized variation of flow patterns (pressure and vorticity contours) and engineering parameters (strain energy transfer and hydrodynamic forces). Structural flexibility leads to the storage (release) of strain energy to the foil (surrounding-fluid) at certain (remaining) time duration. The storage (release) correspond to the accelerating (decelerating) phase of the pendulum-like motion of the foil – for an optimum structural stiffness which leads to the maximum thrust generation. The optimum as compared to other stiffness values leads to maximum deflection of the tip of the foil. This work gives fundamental insights into the physics of momentum transfer in the flexible foil which can lead to a more efficient propulsion system in the future.