Circuit representation of ducted hydrokinetic turbines based on blade element momentum method

Hydrokinetic turbines are designed and deployed worldwide due to the vast scale of hydrokinetic energy existing in tidal streams, ocean currents, and riverine flow. Duct augmentation is a design feature potentially to improve power extraction, reduce maximum stresses, and reduce the cost of electricity. However, there is a lack of computationally efficient and accurate predictive models to evaluate and compare ducted and open turbines. This research proposes a lumped circuit representation model for ducted hydrokinetic turbines. The equivalent duct, rotor, and wake resistances are derived from the control volume analysis based on the axial momentum theory and blade element momentum method. The wake resistance, which represents the viscous mixing loss in the very far wake, is critical for turbine farm design. The duct resistances, which depend on the duct thrust, efficiency, and duct-rotor interactions are identified by computational fluid dynamics. Based on the proposed model, parametric investigations of distributed rotor thrust, torque, power, and wake loss for different duct and blade geometries are conducted. The model can facilitate preliminary parametric design, co-design, real-time control to enhance power extraction and dynamic stabilities, and turbine farm design. A design optimization case is demonstrated to illustrate the utility of the proposed model.