Experimental investigation of fluid–structure interaction in a bird-like flapping wing

Abstract

Fluid–structure interaction in a bird-like flapping wing is investigated experimentally. Various materials having varied thickness (t), elastic property (E) and density (ρw) are selected as the wing for the flapping motion. Force and power measurements are performed in wind-off condition for a range of flapping frequencies. The effect of rib orientation, position of the single spanwise rib along the wing chord and multiple spanwise ribs on thrust generation is also investigated. Dynamics of the flow around different wing configurations are elucidated based on Phase-locked 2D Particle Image velocimetry (PIV) measurements. We found that the strength and size of trailing edge vortex (TEV) are closely related to the stiffness characteristics of the wing. The strength and size of TEV are found to increase with an increase in the stiffness of the wing. Based on thrust generation and TEV characteristics, we noted that the effect of rib is not identical for two different wing materials. The non-dimensional stiffness (Πe∗) for various wing without rib configurations is calculated. We found a non-linear correlation between coefficient of thrust (CT∗) and non-dimensional stiffness (Πe∗) for specific wing configurations. The major findings from this study suggest that wing stiffness cannot be the sole factor influencing the thrust generation. Apart from the wing stiffness, wing deformation especially the trailing edge (TE) deformation pattern might have a major role in thrust generation and there is a need to quantify the deformation either experimentally or computationally.