Abstract
The Flettner rotor is attracting increasing attention as a viable technology for wind-assisted ship propulsion. Nonetheless, the influence of the Reynolds number on the aerodynamic performance of rotating cylinders is still unclear and under debate. The present study deals with a series of wind-tunnel experiments on a large-scale Flettner rotor in which the forces and pressures acting on the cylinder were measured for Reynolds numbers as large as Re=1.0⋅106. The rotating cylinder used in the experimental campaign had a diameter of 1.0 m and span of 3.73 m. The results indicate that the lift coefficient is only affected by the Reynolds number in the critical flow region and below velocity ratio k=2.5. Conversely, in the velocity ratio range 1<k≤2.5, the drag coefficient is markedly influenced by the Reynolds number over the entire range of flow conditions analyzed. The power coefficient scales with the cube of the tangential velocity and it appears to be insensitive to the Reynolds number or whether the cylinder is spun in an air stream or in still air.
Highlights
The Flettner rotor is a rotating cylinder that generates an aerodynamic lift due to the Magnus effect
The present study deals with a series of wind-tunnel experiments aimed at a better understanding of the Reynolds number effects on the aerodynamic performance of Flettner rotors
The results indicate that, within the range considered, there is a remarkable influence of the Reynolds number on the lift and drag coefficients below velocity ratio k 1⁄4 2:5
Summary
The Flettner rotor is a rotating cylinder that generates an aerodynamic lift due to the Magnus effect. But certainly not less troublesome, are those related to the CFD simulations of a rotating cylinder at high Reynolds numbers In this respect, the results of (Zhang and Bensow, 2011) are exemplary: for a same condition, the lift and drag coefficients show a considerable scatter depending on the type of flow solver employed for the computations. The results of (Zhang and Bensow, 2011) are exemplary: for a same condition, the lift and drag coefficients show a considerable scatter depending on the type of flow solver employed for the computations In this context, the present work deals with a series of wind-tunnel experiments aimed at the understanding of the Reynolds number effect on the aerodynamic coefficients of a rotating cylinder in a critical and supercritical flow regime. A set of different Reynolds numbers was investigated, being, respectively, Re 1⁄4 1:8 Á the lowest and Re 1⁄4 1:0 Á the highest Reynolds numbers achieved
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