In order to recover the small hydraulic energy in extra-low head but enough flow rate, the output characteristics of a semi-immersion type undershot water turbine was evaluated by the water funnel test. The momentum of the main flow was exchanged to the output power of the water turbine by the primary blade faced to the main flow. In the case of such kind of water turbine, it is effective to design the number of blades appropriately small number not to be impeded the conversion from the momentum of the main flow to the angular momentum of the primary blade. Furthermore, we clarified that when the pitch angle of the primary blade is designed to be perpendicular to the main flow, it is possible to effectively recover the small hydraulic energy of extra-low head.

A noise problem at a low flow rate of multi-blade centrifugal fan was investigated experimentally in terms of low frequency fluctuation in flow by using a time resolved PIV. The present PIV equipment makes blade by blade passing observation be possible to detect the low frequency velocity fluctuation without blade passing fluctuation, because the data acquisition rate was set equivalent to BPF. The experimental results show that the flow at the impeller outlet has a large fluctuation locally, in the present case, at the scroll angle θ=120°. This fluctuated flow was transported to the downstream in the scroll casing, which passed along the outside of the main flow exited from the impeller. This fluctuated flow was divided into a reverse flow to the impeller and a flow towards tongue in the vicinity of the scroll exit. The reverse flow returned again near θ=120° through the impeller towards the scroll casing. Thus, it was confirmed that the low frequency noise was generated due to this circulating fluctuation.

The flow and sound fields around a small axial fan in a duct are directly predicted based on the compressible Navier-Stokes equations, where the flow around rotating blades is reproduced by the volume penalization method. The computational methods are validated by comparing the predicted performance and the sound pressure spectrum with those measured. Moreover, the effects of the slits in the casing on the flow and sound are focused on. It is shown that more intense tip vortices are generated in the casing with the slits compared with that without a slit. In the wake of the fan, the regions with velocity deficit due to the tip vortices are formed in addition to those in the downstream of the blades. As a result, the radiated sound due to the wake and the struts is affected by the slits of the casing.

Rotor dynamic (RD) fluid force generated in turbomachinery has significant influence on stability of the entire rotor system. Therefore, in order to improve system reliability, predicting RD fluid force from the initial design stage is important. In this study, a coupled analysis method of finite difference analysis of RD fluid force acting on an annular plain seal and shaft vibration analysis of simple rotor system is constructed. In this analysis method, both calculations of fluid force and shaft motion are performed at the same time considering the interaction between them. Using the constructed coupled analysis method, the behavior and stability of the rotor system in the case of large whirl amplitude where the nonlinearity of fluid force becomes prominent are investigated. Moreover, domain of entrainment of stable equilibrium position is focused, and the influence of pre-swirl ratio on this domain is investigated.

A CFD model has been constructed to numerically validate the wind tunnel model of a small vertical-axis wind turbine with a motor-driven variable-pitch mechanism for which we previously reported the result of wind tunnel tests. The test turbine has a radius of 0.18 m, a diameter of the rotating shaft of 0.02 m and three blades with the airfoil section of NACA0015 and chord length of 0.08 m. 2-D Unsteady Reynolds Averaged Navier-Stokes equations with k-k_L-ω turbulence model are solved to simulate a flow around the test turbine rotating at a constant tip speed ratio (TSR) using OpenFOAM. From the simulation results of sixteen cases consisting of two blade conditions of fixed-pitch (FP) and variable-pitch (VP), and eight TSRs of 0.3 to 1.7 with 0.2 increments in one uniform flow of 4 m/s, it has been confirmed that the power coefficients for VP cases become larger than those for FP cases.