Wind energy generation by forced vortex shedding

Oscillating wind energy conversion systems that rely on vortex-induced vibrations (VIV) suffer from low energetic efficiency, but active flow control can produce significant improvements. This research investigates wind energy generation resulting from alternating slot blowing (ASB) on a circular cylinder, experimentally and theoretically. On the basis of measured peak lift coefficients, a low momentum coefficient (<0.04) excitation regime and a high momentum coefficient (>0.04) forcing regime were identified. In the excitation regime, a clear amplitude peak was observed close to the nominal natural vortex shedding frequency. In the forcing regime, separation or circulation control time-scales resulted in mild peaks at approximately half of the natural shedding frequency. In all regimes, the natural vortex shedding amplitudes were exceeded; in particular, by up to a factor of three in the forcing regime. Using a mathematical simulation model, it was shown that an ASB system produces 3.8 times higher net peak power coeffcients − comparable to small wind turbines − with a 7.3 times greater bandwidth than a conventional VIV energy harvester. Economic benefits can potentially be realized by significantly upscaling the system and adding a second degree-of-freedom. Future research will focus on improved slot design, supercritical flow excitation and forcing, and non-linear mathematical modelling of the dynamical system.