Toward improving the performance of a variable pitch vertical axis wind turbine (VP-VAWT), Part 1: Sensitivity analysis using Taguchi-CFD approach

Vertical axis wind turbines (VAWTs) are feasible to be improved due to lower efficiency compared to the horizontal axis type and suffer from fatigue issues as a result of cyclic aerodynamic loading. The performance of VAWTs can definitely be enhanced by utilizing a variable pitch angle mechanism and specific-efficient airfoils, especially at low tip speed ratios (TSRs). With this background, the scope of the present investigation is 2-fold. In the first part, Taguchi and computational fluid dynamics (CFD) methods will be used to perform a thorough sensitivity analysis. Then, in the second part, a multi-objective optimization problem will be defined based on the results of part-1 to address the mentioned drawbacks. This part proposes a novel procedure to accomplish sensitivity analysis. A MATLAB code was used to automatically manage suitable simulations for implementing the proposed innovative statistical-aerodynamic analysis. Five objective functions are offered, including power indices, structural and fatigue demands. Design variables consist of 12 parameters related to the pitch angle profile and the blade section geometry. The sensitivity analysis was implemented in three main stages: executing various simulations under distinct conditions based on orthogonal tables, assessing the hypothesis of using different pitch angle profiles for each blade instead of the same pitch profile for all blades, and describing sensitivities using signal-to-noise ratio (S/N) analysis. The same pitch profile idea was proved appropriate based on the results. The third stage result would reflect the order of importance of design variables regarding each objective in detail. Finally, the best-simulated cases are reported and different aerodynamic aspects will be explored. By using the proposed modifications, both upwind and downwind power performance could be enhanced. However, the fatigue problem could be reduced by lowering the maximum local moment coefficient. The integrated systematic approach used in this paper could be considered a unified framework for sensitivity analysis of variable pitch wind turbines.