The rotor is intended for propelling a fluid or being driven by fluid flow. It consists of a surface (z) which is first twisted (n) about its longitudinal centre line to form a helical band on the outer surface of an imaginary cylinder. After this, the band is formed such (m) that the central axis of this cylinder forms a circle, a helix or a spiral about the centre line (R) of the rotor. When formed (m) into a circle, Moebius-ring fashion, this circle preferably lies in a plane at right angles to the rotor axis, and the ends of the band (i.e at the two ends of the imaginary cylinder) are connected (i.e the band is wound around an imaginary torus). When provided with an armature winding the rotor may be used in a turbo-generator or a turbo-compressor.