Author(s)

G. Dumas & T. Kinsey

Abstract

A wing that is both heaving and pitching simultaneously may extract energy from an oncoming flow, thus acting as a turbine. The theoretical performance of such a concept is investigated here through unsteady, two-dimensional laminar flow simulations using the finite volume, commercial CFD code FLUENTTM. Computations are performed in the heaving reference frame of the airfoil, thus leaving only the pitching motion of the airfoil to be dealt with through a rigid-body mesh rotation and a circular, non-conformal sliding interface. This approach offers the benefit of second order time accurate simulations. For a NACA 0015 airfoil at a Reynolds number of Re = 1 100, a heaving amplitude of one chord (H0 = c), and a pitching axis at the third chord (xp = c/3), we present a mapping of power extraction efficiency in the frequency and pitching amplitude domain: 0 < fc/U∞ < 0.25 and 0 < θ0 < 90◦. Remarkably, efficiency as high as 34% is observed as well as a large parametric region above θ0 > 55◦ of better than 20% results. Impact of varying some of the fixed parameters is also addressed. Keywords: oscillating wing, pitching and heaving airfoil, unsteady aerodynamics, power extraction, turbine, wind energy, flow simulation, finite volume method, accelerated reference frame. 1 Introduction Following the work ofMcKinney and DeLaurier [1], it has been proposed in recent years to use systems of oscillating wings, heaving and pitching with large amplitudes, to develop alternative turbine designs for applications in air (wind turbine) and in water (tidal energy system). Our ongoing investigation [2] aims to establish the actual potential of the concept. In this paper, we restrict ourselves to the canonical case of low-Reynolds number, 2-D incompressible laminar flows for which modern CFD tools can yield reli-

Keywords

oscillating wing, pitching and heaving airfoil, unsteady aerodynamics, power extraction, turbine, wind energy, flow simulation, finite volume method, accelerated reference frame.