Predicting and optimizing the energy-generation performance of an in-stream turbine operating with twin, unconfined, counter-rotating screws by means of CFD Modeling

The overall objective of this numerical investigation consists of predicting and optimizing the energy-generation performance of an in-stream turbine undergoing preliminary design. This turbine is unconventional as its energy extraction surfaces are composed of twin, counter-rotating, unconfined screws aligned at an oblique angle with respect to the water current. First, a cost-effective computational fluid dynamics (CFD) model of the water flow in the vicinity of the turbine was implemented in a commercial package. This CFD model was benchmarked by comparing predicted power coefficient values with available, empirically-obtained, data provided by the client. During this benchmarking exercise, it was determined that a rotating (sliding) mesh approach was necessary to obtain accurate predictions. The CFD model was then used to predict power coefficient values over a range of tip-speed ratios at the design free-stream water velocity for the proposed (initial) screw design. Lastly, simulations were performed to investigate the performance of additional screw designs in the hope of optimizing the energy-generation performance while respecting the provided design constraints.