Back to the Future? A Re-examination of the Aerodynamics of Flettner-Thom Rotors for Maritime Propulsion

The paper examines, by way of a 3-dimensional, unsteady-RANS analysis, the high-Reynolds-number turbulent flow normal to a cylinder rotating about its axis, thus continuing the re-evaluation of this flow configuration as a potential means of providing low-cost ship propulsion. Comparisons are made between the available experimental and LES data both for the bare cylinder, as employed in Flettner’s notable Atlantic crossing, and the variant advocated by Thom in which close-packed discs are distributed along the cylinder. Our results display close agreement with available experimental and LES data other than the results of Thom (1934). We conclude that the addition of discs by the latter led, at the relatively low Reynolds numbers of his experiments, to the boundary layer on the cylinder being thinned to a point at which the boundary layers became laminar or transitional, thus leading to higher lift coefficients than pertain in turbulent flow.