Air-separators are one of effective methods to suppress stall phenomena of axial flow fans. In the present study, numerical investigations are carried out to clarify the stall suppression mechanisms of the air-separator using an axial flow fan with and without the air-separator which are examined experimentally by Yamaguchi et al. The comparisons between numerical and experimental results show reasonable agreements. The results show that a backflow region around the rotor tip is removed at the low flow rate and that the blade loading around the blade tip is increased by the air-separator. Consequently the pressure performance at the low flow rate is improved significantly. Additionally, influences of flow rate through the air-separator and air-separator geometries are also examined to clarify the air-separator effects.

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The machine Reynolds number and the specific speed of centrifugal blood pump are lower than conventional pumps, therefore, it is difficult to apply a general design method. In this research, CFD analysis was done to examine the influence of shape of impeller and volute on the performance and internal flow of adult and pediatric centrifugal blood pump. Moreover, the method of the design of pump that is appropriate for low specific speed and low mechanical Reynolds number were examined. As a result, the efficiency of the blood pump increases by miniaturizing the impeller diameter and enlarging the vane height, and the ratio of the vane height and impeller diameter has an appropriate value. Furthermore, the specific speed with the viscosity ratio expands the coverage of a centrifugal pump, and the efficiency of a centrifugal pump that uses the working fluid with high viscosity can be estimated.

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Recently, fans have been used in order to cool the interior of electronics. A sirocco fan has been used in a narrow place especially because it has the characteristics of high pressure and high flow rate. But the noise of the sirocco fan becomes loud easily so it's very important to reduce the noise of the sirocco fan. So far, there were a lot of attempts to reduce the noise of the fan by performing experiments and numerical analysis. However, there is little knowledge regarding the sirocco fan with a small number of blades. There is an advantage that can reduce the production cost of the sirocco fan if it has a small number of blades. The purpose of this study is to clarify the flow field around the blade of a small sirocco fan with a small number of blades, using LES. As a result, it was suggested that the fast reverse flow appeared between blades at θ=330deg in high flow rate points (Q=0.0321 m³/s, 0.0178 m³/s). Because of the changing flow field, pressure fluctuation around the blades and between the blades became higher easily. Moreover, it was acquired that the pressure fluctuation decreased by the flow reduction.

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The stability analysis with utilizing the lumped parameter piping system was performed in the double-suction centrifugal pump. Cavitation surge was observed in the region of the negative gradients of suction performance curve at low cavitation numbers. The cavitation compliance K and mass flow gain factor M, which represents the dynamic characteristics of cavitation, were evaluated by combining the stability analysis with the several experimental data. The values of K and M were distributed near the analytical neutrally stable lines. Both the experimental and analytical results show that the higher flow rate produce the narrower region of cavitation surge. These results indicate that the analytical results agree with experimental ones qualitatively, and the analysis proposed here is available and the K and M are reasonably estimated.

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Thermodynamic effect of cavitation is a favorable effect for pumps, in which cavity volume is suppressed and available net positive suction head of the pump will be improved. When evaporation occurs in low pressure region inside the pump, local temperature is decreased by the latent heat, the local saturated pressure decreases, then the cavity is suppressed. The thermodynamic effect is known to appear when the main stream temperature closes to critical temperature of the fluid. In institute of fluid science of tohoku university, in order to clarify the basic characteristics of the thermodynamic effect of cavitation, high temperature and high pressure water tunnel is constructed, in which the main stream temperature can be increased to 140°C. And a high accuracy measuring technique of temperature inside a cavity is developed in the present study.

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