Abstract
This paper presents numerical studies of the Magnus effect for a kinetic turbine on a horizontal axis. To focus on the Magnus blade, a single self-spinning cylindrical blade is assumed. An iterative direct-forcing immersed boundary method is employed within the Eulerian-Lagrangian framework due to its capability to treat complex and moving geometries. The Eulerian fluid domain is discretized using the finite volume method while the Magnus rotor is represented by a set of discrete points/markers. The aim of the numerical studies is to provide insights for the design process and predict aerodynamic performances under various operating conditions. Results for stationary and self-spinning cylinders in turbulent flows are found to be in good agreement with published data. By increasing the aspect ratio of the cylinder (simulated segment length over its diameter) from 3 to 10, a 30% drop in lift coefficient and a 22% increase in drag coefficient were observed, which is believed to be attributed to an enhancement of the three-dimensionality of the near-wake. For the Magnus rotor, key parameters such as dynamic forcing and frequency, distribution of pressure coefficient and torque have been produced for two cases with different structural designs and working conditions. With increase of the aspect ratio from 3 to 10, stable forces are observed from the root side of the blade and the torque coefficient increases from 0.68 to 2.1, which indicates a superior performance in terms of power extraction.
Highlights
The Magnus effect is a method of producing lift forces around a rotating body when placed in the cross-flow of a fluid, and can be observed in a wide range of disciplines and applications, such as the curving motion of a spinning ball in various field sports
3 Results for a single spinning cylinder To show the accuracy of the adopted numerical methodology, two validation cases were selected for an infinite length cylinder in turbulent flow with a Reynolds number Re = 1.4 × 105 and velocity ratios α = 0.0 and 2.0
The effect of the aspect ratio (AR = L/D) on the key performance characteristics is numerically investigated for a spinning circular cylinder with finite length in turbulent flow at Re = 1.0 × 105 and α = 2.0
Summary
The Magnus effect is a method of producing lift forces around a rotating body when placed in the cross-flow of a fluid, and can be observed in a wide range of disciplines and applications, such as the curving motion of a spinning ball in various field sports. Mittal & Kumar [4] reported the effect of velocity ratio on the lift coefficient and vortex generation in a laminar flow of Re = 200 They suggested that an increase of the aspect ratio of the cylinder (spanwise length/diameter) plays an important role in the increase of lift and the decrease of drag. Another proposition to improve the lift coefficient on a rotating cylinder was made by Thom [5], who suggested adding endplates to the cylinder which was later proved to be effective by the research of Badalamenti & Prince [6]
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