Design and analysis of Tidal turbines via a nonlinear optimization technique coupled with a BEM

In this paper, a nonlinear optimization method is coupled with a boundary element method (BEM) to design optimum ocean current turbines, and some preliminary results are presented. The optimum turbine geometry is designed to produce the highest power output under several initial constraints. The coordinates of the blade are defined using a B-spline geometry with 4×4 control points being the parameters to be optimized for a given thrust/inflow in the absence of any cavitation. The design process is repeated in an iterative manner by a fully automated interface, which interacts between the hydrodynamic BEM and nonlinear optimization method until the blade geometry becomes fully stabilized, producing maximum power. The present method is first applied to ocean current turbines in open water condition to investigate the influence of design constraints and wake alignment models on the optimal efficiency of the designed blades. full-blown RANS simulations are conducted separately to validate the predicted analysis results using the optimal blade geometry. Comparisons show satisfactory agreement between the results from the present method and those from viscous simulations, and importantly a significant impact of the wake alignment model on the turbine blade design.