A Low Cost Oscillating Membrane for Underwater Applications at Low Reynolds Numbers

Abel Arredondo-Galeana,Aristides Kiprakis,Ignazio Maria Viola

doi:10.3390/jmse10010077

Abel Arredondo-Galeana, Aristides Kiprakis + Show 1 more

Open Access

https://doi.org/10.3390/jmse10010077

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Abstract

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.

Highlights

Flow separation on lifting surfaces such as wings, fins, and blades, is often an undesirable phenomena that occurs when the boundary layer of a fluid flowing over a solid surface loses momentum due to an adverse pressure gradient and the streamlines no longer follow the solid contour [1]
The aim of the test in air was to check the operation of the assembly, whilst the test in water was performed to check that the membrane would deform under hydrodynamic loads
It is worth noting that the trend in results presented here are in line with the trends found by Jones et al [40] at low Reynolds with periodic surface morphing in wind tunnel experiments

Summary

Introduction

Flow separation on lifting surfaces such as wings, fins, and blades, is often an undesirable phenomena that occurs when the boundary layer of a fluid flowing over a solid surface loses momentum due to an adverse pressure gradient and the streamlines no longer follow the solid contour [1]. If the adverse pressure gradient is too high such as at a high angle of attack, the flow remains separated [6,7] Both the LSB and flow separation, are detrimental to the performance of a foil and result in an undesirable increase in drag (D) and, often, in a loss in lift (L) too. In this paper we are interested in the case where the flow remains detached and the operation of devices that rely on high lift to drag ratios is detrimentally affected In air, such is the case of wind turbines [8,9], aircraft [10], and unmanned aerial vehicles (UAVs) [11], whilst in the marine environment examples include tidal turbines [12,13,14], wave cycloidal rotors [15,16,17], flapping energy harvesters [18], propeller blades [19,20,21], and control surfaces of underwater autonomous vehicles (AUVs) [22,23]. Due to the negative repercussions and wide range of scenarios where flow separation occurs, there has been a vast amount of research and methods developed to prevent or minimise flow separation

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