The purpose of this study is to examine the influence of nozzle shape on the performance and effect of wave conditions on the performance and internal flow of a direct drive turbine (DDT)model for wave energy conversion. The performance of the turbine is calculated by the variation of nozzle shape using a commercial CFD code. Moreover, Three kinds of test turbine models are adopted for the experiments of performance test and internal flow visualization. All the experiments using the test turbine models have been conducted in a 2-D wave channel. Regular waves by various wave conditions of wave height and wave period are applied to the turbine performance test. Influence of turbine configuration by several combinations of turbine nozzle shapes and attachment devices on the turbine performance is also investigated.
The results of CFD analysis show that nozzle shape should be designed considering wave height and flow rate entering to the turbine. Best efficiencies of the turbine by 4 types of the nozzle shape do not change largely but overall performances vary mainly by the cross-sectional area of nozzle inlet. The output power of the cross-flow type hydro turbine changes considerably by the nozzle shape, and a partial region of Stage 2 in the runner blade passage obtains maximum regional output power in comparison with the other region of the runner blade passage.
Experimental results show that rotational speed, differential pressure, inflow flow rate, maximum output power and best efficiency of the turbine model vary considerably by the wave conditions. Number of rotation time series data of no load condition is shown change of 10%. When wave height rises, the performance increases.(H=20cm , P_(T)=7.2W , η=45.5% -> H=26cm , P_(T)=11.9W , η=51.6%) Installation of front guide nozzle and rear water reservoir to the test turbine improves the turbine performance. Large passage vortex occurs both at the front and rear nozzles in turn by reciprocating flow in the turbine passage.