This paper shows results of flow field measurements around a horizontal axis wind turbine in various yawed flow conditions and pressure distribution measurements on a rotor blade of the wind turbine. These measurements were carried out with 2.4m-diameter rotor with pressure sensors and a 2-dimensional laser Doppler velocimetry for each azimuth angles in a wind tunnel. As the results, aerodynamic forces of the blade based on the pressure measurements change according to the angle of attack during rotation. So wake of the yawed rotor becomes asymmetric for the rotor axis. Furthermore, the relations between aerodynamic forces and azimuth angles change according to tip speed ratio. By the analysis of the results, relations between the flow field and the aerodynamic forces for each azimuth angles were clarified.

View full abstract

Numerical and experimental studies were done on unsteady flow in a pump sump to study the generation of air core vortex and submerged vortex, which cause vibration and acoustic noise. The geometry of the free surface in the test pump sump was visualized by Moire method, and velocities near pump suction were measured by PIV. Unsteady flow in the pump sump was calculated using VOF method in a commercial CFD software, and calculated velocities as well as free surface geometry were compared with measured ones. The present study showed that CFD can capture unsteady flow in a pump sump with a reasonable accuracy, and that the air core vortex as well as submerged vortex can be predicted by CFD.

View full abstract

Longitudinal vortices produced by the interaction between jets and a free stream are useful to enhance the boundary layer mixing and have proven effective in the control of flow separation. This technique is known as the vortex generator jet method. The vortex generator jet method is an active control technique that provides a time-varying control action to optimize performance under a wide range of flow conditions because the strength of longitudinal vortices can be adjusted by varying the jet speed. In the present study, an active separation control system using vortex generator jets has been developed and can be practically applied to the flow separation control of a two-dimensional diffuser. The proposed system can be operated just before the onset of flow separation, and the separation control is always attained with no flow separation. For the proposed system, if the system starts the operation just before the onset of separation, the total amount of energy to suppress separation can be reduced in contrast to the original feedback system, which starts the operation after separation occurs.

View full abstract

A sea trial of wave power plant using an impulse turbine for bi-directional airflow has been carried out at Niigata-nishi Port, in order to demonstrate usefulness of the turbine. The wave power plant using OWC has been installed at the side of a breakwater and has an air chamber with a sectional area of 4m²(=2m x 2m). The impulse turbine used in the sea trial has fixed guide vanes both upstream and downstream, and these geometries are symmetrical with respect to the rotor centerline in order to rotate in a single direction in bi-directional airflow generated by OWC. As a result, it was concluded that total conversion efficiency of the plant using the impulse turbine is superior to Wells turbine which is the mainstream of turbine for wave energy conversion. Further, the performance of wave power plant was predicted by numerical analysis and it was compared to the experimental data.

View full abstract