Numerical Investigation of the Energy Harvesting Capabilities of Naca Series Flapping Foil Turbines in Swing-Arm Mode

Abstract

In recent years, the academic community have shown an increased interest in flapping-foil turbines in swing-arm mode, due to their increased capacity to extract power and greater efficiency compared with simple mode flapping-foils. This paper numerically investigates the effect of the foil’s shape on the power extraction, by modelling the flow around several 4-digit and 5-digit 6-series NACA foils. The maximum thickness, maximum camber, location of maximum camber, and location of minimum pressure are all varied. The numerical solver combines two methods, Finite Element and Level-Set, to obtain the flow field around a flapping-foil in swing-arm mode at a Reynolds number of 1 × 10 5 , swing factor of 0.25, and non-dimensional reduced frequency parameter of 0.08. The purpose-developed two-dimensional Navier-Stokes solver was validated using excising numerical and experimental results. A study of the vortex structure around a flapping-foil in swing-arm mode was performed to understand the relation of the leading-edge vortex creation, growth, and separation with the extracted power. Results show the foils, NACA5415, and NACA63015, are recommended for flapping-foil hydrokinetic turbines in swing-arm mode, as they have the highest power coefficient of up to 0.4, which is significantly higher than the other tested hydrofoils. erest in flapping-foil.

Keywords: Energy harvesting, Flapping foil turbine, Swing-arm mode, Leading-edge vortex, Finite Element Method, Level-Set Method