Low and High Fidelity Aerodynamic Simulations for Airborne Wind Energy Box Wings

Abstract

Airborne wind energy systems convert the kinetic energy of wind into usable power. In general terms, this power is proportional to the ratio CL3/CD2 of aerodynamic coefficients. From a structural perspective, the thickness-to-chord ratio of conventional AWE wings needs to be high to withstand the high aerodynamic loads. The box-wing concept opens the possibility of exploring a broader range of airfoils since structural loads can be redistributed with reinforcements between the two wings. This study aims to develop an automatic process for constructing a finite volume CFD mesh from a parametrized box-wing geometry, which is generally the most time-demanding part of CFD analysis. These analyses provide an accurate estimate of the viscous drag acting on box wing designs. In addition, this study aims to define a criterion of equivalence between a box wing and a conventional wing, and obtain the reference design by optimization using panel methods for fast aerodynamic computations. The aerodynamic tools used for this study are a steady panel method (APAME) and Reynolds Averaged Navier-Stokes simulations using a k-ω SST turbulence model (OpenFOAM). The computational framework is ultimately suitable for aero-structural optimization of a boxwing because of the high degree of automation and the reduced number of design parameters.