A novel wave energy device (the 'Wave Rotor') is driven by the action of the Magnus effect on two parallel counter-rotating cylinders. This paper presents the results of experimental investigations of a model wave rotor both driven in still water and absorbing energy from incident waves, together with data on spinning cylinders in uniform steady flow and in waves. An estimate is made of the productivity of a full-scale device.
The wave rotor (Retzler 1991) comprises cylinders that span between arms that turn about a central axis parallel with the wave crests (figure 1). Circulation in opposite senses around the two cylinders generates lift forces producing a moment about the central axis. In orbital flow the device rotates continuously at the wave frequency and power is extracted by providing damping to the rotation. Magnus lift forces on spinning cylinders in waves can be several times larger than the inertial forces depending on spin magnitude and wave size (Budal & Lillebekken 1985, Retzler 1987), offering the potential of a wave energy device of higher power for a given displacement. An earlier lift-driven wave energy device has been described by Hermans, van Sabben and Pinkster (1990). It used a foil, mounted on a shaft immersed in waves, which also performed full rotations synchronously with the waves. The device described here uses two cylinders for lift to give a couple around the centre of mass, hence requiring no counterbalance. Furthermore a spinning cylinder, unlike a foil, has no angle of attack and hence does not stall.
The experiments were carried out in a wave flume 12.8m long, 0.425m wide, with a water depth of 0.7m. An electricallydriven absorbing wavemaker with force feedback generates waves over a frequency range of 0.5 – 2.0Hz.
