Experimental investigation of an optimised pitch control for a vertical-axis turbine

This study reports on an experimental method to obtain the motion law of a pitch system required for maximising the power output of a vertical-axis water turbine (VAWT). In order to allow for the close monitoring of blade forces, the turbine is modelled with a single oscillating hydrofoil in a water channel. The pitch motion is controlled numerically, and the pitch angle and forces are measured as a function of time. The objective of the optimisation is to maximise the time integral of the thrust coefficient. The optimisation is based on a hardware-in-the-loop method and uses a multi-scale, full-factorial approach. The optimal motion law is found through successive improvements with an adaptive parameter step refinement, while the integral of the driving force coefficient is used as a target function. An optimal pitch trajectory with a significant improvement in the thrust coefficient was obtained for a single operating point. The benefit of this methodology is the possibility to study a complete range of turbine designs through the variation of two dimensionless parameters (tip-speed ratio $\lambda $λ and reduced frequency k ), within very short runtime, minimising time and costs investigation, compared to more common numerical methods, or experiments on a complete VAWT.