As a self-rectifying turbine for wave energy conversion, the new versions of impulse-turbine with self-pitch-controlled tandem guide vane are proposed. These include (1) variable-pitch flat-plate type and (2) variable-pitch splitter type. In order to examine the unsteady characteristics of the turbines, the experimental investigations have been made by a special turbine equipment and flow visualization using smoke wire method. The result shows that a high-efficiency impulse turbine can be developed through the use of the splitter. It is found that, in this case, the upstream guide vanes act as a slotted nozzle blade row and the downstream vanes as a tandem diffuser blade row by changing the pitch angle of the splitter automatically in a reciprocating flow
