This paper describes work involved with modelling, using the CFD package FLUENT, a contra-rotating double row set of 3 bladed tidal turbines. The design of these turbines is to assess the potential increase in the power, torque and axial thrust generated over a conventional single row propeller.
A single row 3 bladed horizontal axis tidal turbine (HATT) has been created and validated with data from a 0.5 m diameter laboratory scale turbine. This data has then been scaled up to 10 m diameter turbines. A series of models have been produced at the 10 m diameter scale which incorporates 2 rows of blades. The spacing between each row of blades has been increased to establish the wake characteristics and the turbine characteristics, in particular for power, torque and axial thrust for each design scenario. Each model is compared against the single row turbine. The row spacing has been non-dimensionalised to the turbine hub diameter to provide a more pragmatic approach to the spacing selection.
The results from the CFD models show that there is a negligible increase in the power generated but an increase in the axial load on the turbine. The nett torque acting on the device is, however, considerably reduced, and potentially negated, so potentially helping the turbine to align to the tidal flow.