||The Performance Assessment of Wave and Tidal Array Systems (PerAWaT) project, launched in October 2009 with £8m of ETI investment. The project delivered validated, commercial software tools capable of significantly reducing the levels of uncertainty associated with predicting the energy yield of major wave and tidal stream energy arrays. It also produced information that will help reduce commercial risk of future large scale wave and tidal array developments.
WG3 WP5 (device scale numerical modelling: detailed CFD of other concepts), Deliverable 2 is concerned with the CFD modelling of a high solidity open-centre turbine, using the same modelling methodology as Deliverable 1. Two key phases of work were undertaken:
The basic analytical model combines the theory for the analysis of high-solidity turbomachines with actuator disc theory, along the lines of the classic blade element momentum theory for low solidity turbines. This allows for the specification of blade angles which should result in good turbine performance at the design tip speed ratio. It is shown that high solidity turbines will produce a thrust coefficient which decreases monotonically with an increase in the tip speed ratio; the opposite qualitative behaviour to that generally observed for low solidity turbines. The underlying reasons for this are explained in the report. Further preliminary work includes basic structural calculations and a consideration of the effect of ducting the high solidity turbine, based on results from WG3 WP1.
- the development of a basic analytical model of a high solidity turbine, in order to support the design of a credible turbine rotor; and
- the CFD analysis of this design, in order to produce results for the velocity field in the wake of the turbine.
The second phase of work is the development of the CFD model. This uses the same modelling methodology as was used for the low solidity ‘generic rotor’ of Deliverable 1.Results from this confirm the prediction that high solidity turbines do show a decrease in the thrust coefficient with an increase in the tip speed ratio. The predicted power coefficient is seen to be lower than that seen for the generic rotor, but nevertheless potentially viable. Longitudinal and lateral profiles of the streamwise velocity in the wake are presented in the same format as in the Deliverable 1 report. From these it is seen that the wake deficitis lower than that seen for the generic rotor, due to the lower thrust coefficients. It is also seen that the structure is notably different, this being primarily due to the ‘internal’ bypass flow that the open-centre of the turbine allows for