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

PurposeCovert 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/approachA 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 degrees 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. FindingsDuring 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/valueThis 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.

Automated summary

This paper investigates the flow control mechanism induced by the dynamic motion cycles of bio-inspired flaplets on a model wing. The experiment results show that the opening of flaplets induces backflow underneath, while the closure generates a forward directed jet, which re-energizes the boundary layer flow upstream. This study provides insights into the action of pop-up feathers for separation control and gust control.