Large Eddy Simulation of Flows Around a Kite Used as an Auxiliary Propulsion System

Abstract

The aerodynamic forces acting on a kite proposed for propelling marine shipping are investigated using computational and experimental means. Attention is given to the kite's positions as perpendicular or nearly perpendicular to the air flow that still possess potential for thrust generation but cannot be analysed using finite wing models applicable for kites at low angles of attack. Good agreement is achieved in the prediction of the time-averaged drag coefficient between the large eddy simulations (LESs) of a full scale kite and wind tunnel measurements of a small scale kite model. At zero-yaw conditions both the time-averaged drag and lift (side) forces show behavior similar to the literature-reported empirical relations for flat plates of the same aspect ratio (AR), but with differences of up to 20% in the coefficients’ values. Thus, the plate’s known empirical formulae for aerodynamic forces at zero yaw angles may be used as fast low-accuracy prediction tools before engaging with the more costly turbulent flow computations and wind tunnel tests. Yawing moderately the kite can actually increase mildly the drag but further yawing or pitching it reduces the dominant drag force. Both the drag and lift show unsteady components that are related to the large turbulent wake behind the kite and vortical shedding from the kite's ends. Power spectra of the aerodynamic forces’ coefficients are presented and analysed.