Due to the high cost pressure in the field of aviation, the further increase in efficiency is in the focus of development. Nowadays, airfoils are highly developed and optimized. Thus, new sophisticated approaches, additional configurations and physical effects at lift generation devices have to be explored in order to further reduce drag and significantly increase lift. Focal point of these considerations is the Magnus effect, in which rotating cylinders generate a lift force. This has already been investigated in the past, in particular, different kinds of surface roughnesses, special rotor geometries, ratios of circumferential speed velocity to free stream velocity, or the effect of end plates have been considered. The Scottish engineer A. Thom achieved a significant increase of the performance by adding so called Thom discs coaxially and equidistantly mounted on the cylinder. Investigations of the Thom disc rotors (Thom rotors) have shown a maximum of the lift to drag ratio for the circumferential cylinder velocity to freestream velocity α = 2. Most of the conducted experimental studies have only delivered integral force values. However, detailed insights in the structure of the flow field are still missing. Thus, in the Computational Fluid Dynamic (CFD) study presented here, one of our objectives is to reveal the three-dimensional flow field characteristics for various rotating Thom rotor configurations in detail. The basic configuration is a rotor with two end discs, a so called Flettner rotor. This configuration is varied by mounting Thom discs on the cylinder equidistantly arranged between the end discs. In order to reduce the variety of possible different configurations it was necessary to concentrate on a subset of the most significant design parameters, such as the cylinder aspect ratio, the end-plate diameter ratio, the thickness of the discs and the number of Thom rotors itself. Also, the cylinder based Reynolds number was set to a fixed value of Re = 3.4 · 10 4 . One special focus of this work has been the impact of the geometrical restrictions of the number of Thom rotors, and, thus, their distance, on the boundary layer, which leads to flow separation. Especially, the vortical flow structures generated at the Thom discs have been analyzed. On each disc the flow topology is separated and rolls up into different tip vortice structures. These vortices influence the pressure field around the cylinder and therefore the generated lift forces are different. Between two facing discs the streamwise velocity component is increased. In the corner of the cylinder and one disc an increased radial flow component must be expected. The combination of these effects leads to an interesting flow topology for each investigated disc distance. Eventually, the main goal is to identify the Thom rotor configuration which shows the highest lift to drag ratio , in fact, our task is to identify the most effective configuration in comparison to the other configurations and the flow phenomena behind.
