In this study, an optimization method which couples a Reynolds-averaged Navier-Stokes (RANS) method and lifting line model interaction method is presented, and applied to design, for highest power output, horizontal axis marine current turbines in uniform inflow for different duct shapes. The flow around duct is solved by the RANS method, where the turbine blades are represented by a pressure drop as a function of radius, based on the lifting line model. An automated tool is developed to generate high-quality meshes for given duct shape and domain size. The present method is first applied to design unbounded ducted turbines and the effect of duct shapes (angle of attack, camber, chord length and thickness) on the power coefficient is studied. Then, ducted turbines placed in a cylindrical channel are designed by this method, built by a 3D printer and tested in a water flume.
Marine current contains vast amount of power and has the potential to be a promising source of renewable energy in many places of the world (Charlier, 2003; Bahaj and Myers, 2004; Grabbe et al., 2009). Since water has a density which is about 1000 times that of air, marine current turbines can be built with a much smaller size than wind turbines. Another advantage of marine current energy is that it is more regular and predictable than the wind energy (Clarke et al., 2006), which is especially favorable when being accommodated within the electricity network.
The marine current turbines can mainly be categorized as vertical and horizontal, depending on the direction of rotational axis of rotors relative to the incoming flow. Studies of the vertical axis current turbines can be seen in Ponta and Dutt (2000), Li and Calisal (2010), Yang and Shu (2012) and Derakhshan et al. (2017). Compared with the vertical axis turbines, the horizontal axis turbines have many merits, perhaps the most important one of which is that the design and analysis theories from the wind engineering and marine propellers are abundant, well established and can be migrated to current turbines (Khan et al., 2009; Liu, 2010).