Ducted Hydrokinetic Turbine Design Optimization Using CFD-based Adjoint Method*

Hydrokinetic turbines are designed to extract energy from different natural water sources, such as rivers or tidal and ocean currents. In order to improve the efficiency of energy extraction, a duct can be used to accelerate and condition the fluid flow passing across the turbine. In this work, we explore optimal design of a ducted hydrokinetic turbine to maximize the hydrodynamic efficiency, which is believed to exceed the Betz' limit (the theoretical limit derived from a bare turbine). For this purpose, we perform optimization on both the blade and duct geometries simultaneously using the CFD-based discrete adjoint method, implemented in an open-source environment DAFoam. The results will be discussed in terms of the maximum efficiency achieved and the effect of duct to turbine performance.