High-fidelity flow simulations of electroactive membrane wings

Abstract

This work is inspired by natural flyers such bats and insects. They show outstanding aerodynamic performance due to their flexible membrane wings and their ability to control its stiffness to improve manoeuvrability. In this work the fluid-structure coupling as well as the physics and the control of electroactive membranes have been simulated in a multiphysics framework. This study has allowed not only to have an insight of the flow mechanisms which allow a membrane wing to enhace lift and delay stall at high angles of attack but also lays the basis of the understanding of how an active control of the membrane’s stiffness in response to the unsteadiness of the fluid-structure coupling can deliver a more stable flight. In particular, numerical simulations are conducted for an electroactive membrane wing in a laminar incompressible flow. The fluid-structure interaction problem is simulated for electroactive polymers whose shape and stiffness can be modified by applying an electric potential. The Maxwell stresses generated by the electric field across the membrane produce an in-plane relaxation. Results from this work show that a fixed voltage applied to a prestretched membrane results in an increased camber and therefore enhanced mean lift. Moreover, the effect of a partial activation is considered as well as an oscillating voltage across the membrane. The results presented in this work indicate that the lift is increased at angles of attack up to a = 12 when the back section of the membrane is activated. In addition, lift is increased at higher angles of attack when the voltage oscillates at frequencies close to resonance of the coupled fluid-structure system. Finally, an active control has been simulated exploiting the electromechanical characteristics of electroactive polymers and using the membrane itself as a sensor. This work shows that when the whole surface of the membrane is used as sensor and actuator, a proportional integral control is able to reduce the membrane’s oscillations at medium angles of attack, delivering a more stable flight and smoother response to a gust.

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