Optimization and Validation of Cycloturbine Blade-Pitching Kinematics via Flux-Line Theory

摘要

The newly developed flux-line theory identifies the maximum power harvested by a cycloturbine and the associated fluid-turbine interaction pattern. This work designs blade-pitching functions that maximize turbine power by identifying the blade lift coefficient functions required to optimally decelerate the flow, relating these waveforms to blade angle of attack functions through a novel semi-empirical curvilinear flow aerodynamics model, and finally computing optimal blade-pitch motions with freestream flow data from flux-line theory. At low and moderate tip speed ratios, the blades stall before achieving the required deceleration force. In those cases, more wind power is extracted by braking the flow through both the upstream and downstream portions of the cycloturbine. In a truck-mounted cycloturbine test, the flux-line optimal pitching kinematics outperformed sinusoidal and fixed-pitching kinematics. The turbine achieved a mean gross aerodynamic power coefficient of 0.44 (95% confidence interval: [0.388,0.490]) and 0.52 (95 % confidence interval: [0.426,0.614]) at design tip speed ratios of 1.5 and 2.25, respectively, which exceeds all other low tip speed ratio vertical-axis wind turbines. Two-dimensional Reynolds-averaged Navier-Stokes simulations show that the optimal blade-pitching functions achieve high power coefficients by evenly extracting energy from the flow without blade stall or detached turbine wakes.