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Several models have been proposed to predict the shaft output characteristics of the vertical axis wind turbine from the aerodynamic characteristics of the blade. However, it has not predicted the output characteristics of the small wind turbine, turbine diameter less than 1 m, even the multiple stream tube model included effect of the momentum reduction. A solidity of the small wind turbine become higher than large, i.e. blades interval of small wind turbine becomes short. Therefore, it expects that the wake of preceding blade influence strongly aerodynamic character of following blade. Thus, we have investigated the relation between wake of rotating turbine and its shaft output characteristics. From result obtain, we had cleared the shaft output character agree with variation of momentum loss of the wake of turbine. Moreover, the relevance between the shaft output characteristics and velocity fluctuation in the wake had been found. In the low tip speed ratio region increasing the shaft output, the periodical component synchronized with motion of the blade remarkably appear in velocity fluctuation, and it disappear near the peak of shaft output. Meanwhile, in the high tip speed ratio region decreasing the shaft output, the turbulent component is dominant in velocity fluctuation. It indicates that the blade-wake interference was affected on shaft output of the small wind turbine. Therefore, the purpose of this study was to find out a similarity parameter of the shaft output characteristics based on blade-wake interference. The larger the scale of blade wake or slower the advection velocity of it, the higher the possibility that blade wake generated from previous blade interfere to following blade become. For blade-wake interaction, these two parameters which the scale and the advection velocity of blade wake, are important. Thus, I estimated these parameter in this study using the wind turbine model with single blade. From measurement of the blade wake, I found that the scale of the blade wake depends on the ratio of the rotational speed of the turbine to the free stream velocity, and the advection velocity of blade wake depends on the free stream velocity. From these characteristics of blade wake, I suggest a new parameter based on the blade-wake interaction using tip speed ratio, solidity, number of blade, and turbine diameter. The shaft output characteristics of the small wind turbine indicates good similarity for the new parameter.

It was well-known that a disturbance, introduced artificially into a supercritical laminar boundary layer along a flat plate, is still laminar in the initial stage of its downstream development. Thus, we named it a "laminar spot" because it resembles a turbulent spot though its velocity perturbation remains laminar. From velocity measurements using a rake-type 16-channel hot-wire probe, we found that in the first stage of the downstream development of a laminar spot, its maximum width was at 0.2δ (what is called the critical layer) and one-half of its lateral growth angle was about 5°, which is almost one-half that of a turbulent spot. We call this region a "laminar spot region". In the present study, we measured in detail the velocity field of a laminar spot using a new hot-wire probe in the laminar spot region. The results showed that a laminar spot consists of some hairpin vortices and some induced U-shaped vortices under the hairpin vortices. Because of the interaction of the velocities induced by the respective vortex legs, the legs of the U-shaped vortices were located at the outermost part of the spot. Moreover, the new vortex legs extended spanwise at about 4° as the spot traveled downstream. Consequently, we concluded that the laminar spot grew spanwise in accordance with the span of these vortex legs.

We manufactured a new hot-wire probe (abbreviated as NHP) with two parallel wires placed close together for measuring a transitional boundary-layer flow. The main feature of NHP was that it was much smaller than conventional multi-sensor probes, such as an X-type probe. Thus, the present probe could be regarded as a sensor similar to an I-type probe in configuration;we expected to obtain high spatial resolution for the velocity components. The principle of measurement was very simple so that streamwise and normalwise velocity components were simultaneously obtained from sums and differences of the linearized hot-wire outputs with aid of the look-up matrix method. As a result, we found that although the characteristics between the hot-wire output and flow angle are very complicated, we can obtain simple relations between them if flow angle is confined from -30° to 30°. Moreover, we measured velocity profiles in a low Reynolds number turbulent boundary layer using NHP. From results obtained, it was found that NHP is very useful tool for measuring velocities in a thin boundary layer.