A low cost oscillating membrane for underwater applications at low Reynolds numbers

Active surface morphing is a nonintrusive flow control technique that can delay separation in laminar and turbulent boundary layers. Most of the experimental studies of such control strategy have been carried out in wind tunnels at low Reynolds numbers with costly actuators. In contrast, the implementation of such a control strategy at low cost for an underwater environment remains vastly unexplored. This paper explores active surface morphing at low cost and at low Reynolds for underwater applications. We do this with a 3D printed foil submerged in a water tunnel. The suction surface of the foil is covered with a magnetoelastic membrane. The membrane is actuated via two electromagnets that are positioned inside of the foil. Three actuation frequencies (slow, intermediate, fast) are tested and the deformation of the membrane is measured with an optosensor. We show that lift increases by 1%, whilst drag decreases by 6% at a Strouhal number of 0.3, i.e., at the fast actuation case. We demonstrate that surface actuation is applicable to the marine environment through an off the shelf approach, and that this method is more economical than existing active surface morphing technologies. Since the actuation mechanism is not energy intensive, it is envisioned that it could be applied to marine energy devices, boat appendages, and autonomous underwater vehicles.