Impulsive Start-Up of a Deformable Flapping Wing at Different Angular Conditions

This paper aims at evaluating the influence of the initial rotation on a flapping deformable wing. Scanning PIV techniques are used to obtain the instantaneous volumic velocity fields, which allow the computation of the pressure field and calculation of the forces generated by the wing. The experiments were performed with a flat deformable wing, in order to also see the influence of the wing flexibility on the lift production. Comparing our results to those obtained in previous studies at different Reynolds number (Percin and van Oudheusden in Exp Fluids 56(2):1–19 (2015), [1, Diaz et al., in Comparison between start-up and established flow conditions in deformable flapping wings, pp 2035–2050, (2018), 2]), it was shown how the typical vortical structures that are generated around a flapping wing (Jardin et al., in J Fluid Mech 702:102–125, (2012), [3]) remain stronger, less chaotic and more compact for a longer period of time for a low Reynolds number. The present work further focuses on the role of the initial direction of rotation in this case of study.