On the influence of spanwise deformation on lift coefficient and trailing vortices properties at low Reynolds number

Abstract

We conducted experiments using a single non-deformed and two spanwise deformed wing models for a constant chord-based Reynolds number, Re=20×103. We carried out all experiments to consider several angles of attack α lower than the stall value. The lift forces between non-deformed and spanwise deformed wings present differences depending on the angle of attack. A first finding of the experimental study is that, for smaller values of the angle of attack, e.g., α = 4°, the non-deformed wing case has higher lift values than the highest spanwise deformed wing. However, for larger values of the angle of attack, such as α = 8°, we found a higher lift for the spanwise deformed case. Additionally, velocity fields of the trailing vortex have been taken by two-dimensional particle image velocimetry, finding that both theoretical models by Batchelor [J. Fluid Mech. 20, 645 (1964)] and by Moore and Saffman [Proc. R. Soc. Lond. Ser. A 333, 491 (1973)] can be fitted to experimental measurements obtained from non-deformed and spanwise deformed wing models, the latter model giving the best results for all angles of attack. Finally, we computed the circulation of the trailing vortex using two different methods with the same result and observing that this estimated circulation level directly correlates with the measurement of the lift force.