Design and implementation of spanwise lift and gust control via arrays of bio-inspired individually actuated pneumatic flaplets

Abstract

Purpose Covert feathers on avian wings can show dynamic pop-up behaviour in rapid succession as a reaction to turbulent gusts. The purpose of this paper is to understand the possible flow control mechanism induced during such dynamic motion cycles. A model aerofoil is designed with suction side spanwise control of rows of bio-inspired flaplets. Design/methodology/approach A NACA 0012 aerofoil is equipped with a spanwise row of eight flaplets at 80% chord, connected to pneumatic actuators and can be deployed to max 15° in a prescribed open–hold–close manner. The model is placed in a water tunnel and flow measurements are done in the wake of the flaps during a cycle using particle image velocimetry. Findings During opening, boundary layer flow is sucked into the void space between the wing surface and the flaplet, which induces backflow underneath the flaplet and traps the fluid inside. This fluid is expelled downstream during closure, which generates a forward directed jet as seen by the formation of a vortex-ring like structure with higher axial momentum. The entrainment of the jet leads to the re-energising of the boundary layer flow further upstream. Originality/value This paper presents a furtherment of understanding of the action of pop-up feathers for separation control. The actuation of the bio-inspired flaplets shows a flow vectorising effect which can be used for active separation and gust control. In the case of incipient separation, flaplet action can act to re-attach the flow because of the jet entrainment effect.

Fly by Feel: Flow Event Detection via Bioinspired Wind-Hairs

“…The disturbance generation was realised with a symmetric NACA0012 wing (chord C1 = 30 cm) with four individually controlled pneumatically actuated flaplets, as previously developed in [25]. The pneumatic actuation was since updated from balloons to small pneumatic cartridge cylinders to overcome past repeatability concerns.…”

“…Such distributed flaplets can help to control the distribution of circulation and drag along the span in a sensitive way. Such a wing was designed in our lab [25], and the individually controllable flaplets mimicked the pop-up feathers that birds have. This concept has been used as a disturbance generator in which the flaplets open and close to create a gust-like disturbance, and it will be used in such a way again here.…”