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The aim of this work is to provide an impulse type hydraulic turbine to utilize unexploited water resources as nano hydropower in the mountainous area. The turbine is simplified to make cheap energy and uses inexpensive components for widespread utilization. The turbine model is tested experimentally to reveal the power characteristics. The flow visualization and numerical simulation are conducted to clarify the behavior of free surface flow in the runner with different nozzle positions. The experimental results show that the maximum runner efficiency of the prototype turbine is 0.56. Numerical simulation shows that the output power depends on the nozzle positions with the impingement of the tail of the jet portion to the backside of the blade. This study gives the fundamental information of the turbine performance to acquire a guideline for future practical applications.

The experimental study of flow field and heat transfer characteristics of a submerged, rectangular jet impinging normally on a flat plate is presented. Four nozzle-to-surface spacing of H/w=3, 6, 10 and 20 with acoustic excitations was performed experimentally. The forcing Strouhal number is set from St=0.1 to 0.9 at 0.1 intervals. Velocity distributions with two excitation modes, symmetric and asymmetric excitation, are investigated by means of hot-wire measurement. It was found that the basic flow fields changed drastically, while there is little difference of heat transfer characteristic for both the excitation modes. For the short nozzle-to-plate distances, the heat transfer was enhanced in the wall jet region for the excitation of St=0.2. The maximum heat transfer ratio was obtained at the stagnation point for the middle spacing of H/w=6 for St=0.5. It was revealed that the non-periodic velocity component played the most important role in promotion of the heat transfer with acoustic excited impinging jet.

The aim of this investigation was to develop an environmentally friendly nano-hydraulic turbine. A model of a two-bucket Savonius type hydraulic turbine was constructed and tested in a water tunnel to arrive at an optimum installation condition. Effects of two installation parameters, namely a distance between a rotor and a bottom wall of the tunnel, a rotation direction of the rotor, on the power performance were studied. A flow field around the rotor was examined visually to clarify influences of installation conditions on the flow field. The flow visualization showed differences of flow pattern around the rotor by the change of these parameters. From this study it was found that the power performances of Savonius hydraulic turbine were changed with the distance between the rotor and the bottom wall of the tunnel and with a rotation direction of the rotor.

The aim of this investigation is to develop an environmentally friendly nano-hydraulic turbine. Three type models of Savonius rotor are constructed and tested in a water tunnel to improve and clarify the power performance. Flow field around the rotor is examined visually to reveal the enhancement mechanisms of power coefficient using the double-step rotor. Flow visualization showed the difference of flow patterns at the central section between the standard (single-step) rotor and the double-step one. A meandering flow in the axial direction of the rotor was observed only for the double-step rotor. This flow had the pressure restoration effect at the returning blade's concave side and the torque strengthened effect at the advancing blade's convex side. As a consequence, the power coefficient was 10% improved.

Active control of an impinging jet upon a wedge has been attempted using a sinusoidal excitation of blowing and sucking at the jet exit. The excitation sufficiently enables 'phase-lock', which is synchronization between self-oscillating flow and the excitation, so that hot-wire measurements directly provide phase averaged flow fields and they illustrate appearance of the jet swing in front of the wedge and collision of the jet on one of side of the wedge. It was demonstrated that this control set up is practical not only for illustration of the phase averaged flow field but also for reduction of the edge tone due to the flow oscillation with inverse phase excitation in half of the jet.

For revealing the transition process in a flat plate boundary layer subjected to a weak free stream turbulence, flow visualization and hot-wire measurements were performed. A weak free stream turbulence was generated by a turbulence grid mounted upstream of the contraction. The flow visualization clearly displayed a transition scenario in which a local two-dimensional wave packet rapidly forms a Λ shape structure and then breaks down to turbulence, resulting in the generation of a turbulent spot. Quantitative measurements performed by using a hot-wire anemometer also confirmed the existence of local Tollmien-Schlichting waves that agreed with the parallel linear theory in terms of their frequency, phase velocity, and the wall-normal distribution of band-pass-filtered fluctuations. For comparison, a boundary layer subjected to a moderate-intensity free stream turbulence was investigated. This investigation showed that streaky structures play an important role in the boundary layer transition, as shown by Matsubara et al. [J. Fluid Mech., 430, (2001), 149-168.] A drastic change occurred in the transition process and this change could be sensitively determined by employing the intensity and/or spectra of the free stream turbulence.