Experimental investigation of the aerodynamic performance of Flettner rotors for marine applications

Abstract

Flettner rotors are becoming alternative wind-assisted propulsion systems for marine applications. This study experimentally investigated the aerodynamic performance of large-scale Flettner rotors with a diameter D = 350 mm, 0 = α ≤ 4.5, 3.5 = L/D ≤ 6.0, 1.0 ≤ De/D ≤ 2.0, and 9.33 × 104 ≤ Re ≤ 3.15 × 105, where α is the velocity ratio, L is the cylinder span, De is the diameter of the endplate, and Re is the Reynolds number based on D. The initial, increasing, decreasing, and stable areas were defined to describe the variation in the time-averaged lift-to-drag ratio K‾ with an increase in α. Both the aerodynamic performance of Flettner rotors and the range of the four areas were significantly influenced by L/D, De/D, and Re. Based on the measurement of the aerodynamic forces acting on the tested Flettner rotor under the influence of an interfering Flettner rotor with the same α, the effects of aerodynamic interaction for different wind incidence angles β and spacing ratios S/D were studied in detail. In addition, the driving and heeling force coefficients were presented for the combination of two Flettner rotors. Once the arrangement of the two Flettner rotors installed on the deck of a ship was known, both the driving and heeling forces provided by the combination of these rotors depended on α and the apparent wind angle.