Fluid–structure interaction dynamics of a flexible foil in low reynolds number flows

The present paper numerically investigates the aerodynamic characteristics of a chord-wise flexible filament-like structure subjected to a fluctuating inflow in terms of the wake of a rigid cylinder situated upstream in the low Reynolds number regime (RED = 500, where D is the diameter of the cylinder). The numerical simulations are performed with a strongly coupled partitioned fluid–structure interaction (FSI) solver based on finite volume approach. An incompressible Navier–Stokes solver is used to capture the unsteady viscous flow features and the flexible structural model is considered to be nonlinear and elastic. The foil is fixed at its leading edge, and the structural properties (mass ratio (μ), flexural rigidity (EI), etc.) are chosen appropriately to have a comparable fluid and structural inertia with dominant FSI effects to significantly augment the aerodynamic loads. It can be seen that the chordwise flexibility of the wing manifests a passive pitching achieving greater propulsive efficiency. The deflection envelope reflects the fundamental bending modes of the structure. The interactions between the wake of the rigid cylinder and the flexible structure are investigated with the help of vorticity contours as well as Lagrangian coherent structures to have a clear understanding of the vortex-induced FSI dynamics. Moreover, the aerodynamic forces generated by the flexible foil are compared with that of a rigid stationary foil of same length and subjected to similar upstream flow fluctuations. It is observed that the chord-wise flexibility enhances the lift and thrust generation remarkably compared to the rigid foil.