We developed a high-efficiency half-ducted propeller fan to reduce the electric power consumption of the outdoor unit of a packaged air conditioner by using a design tool combining computational fluid dynamics (CFD) with multi-objective optimization techniques based on a genetic algorithm (GA). The baseline fan was a half-ducted propeller fan with three blades of a currently available product. The objective functions for optimization were fan efficiency and aerodynamic noise. We found there was a trade-off relationship between the static pressure efficiency and the fan noise. We then selected the optimized fan that had the same noise level as the baseline fan but with improved fan efficiency. The blade tip of the optimized fan was curled toward the suction side direction. Finally, we confirmed through experiments that the static pressure efficiency of the optimized fan was increased by 1.8%compared to the baseline fan.

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The system environments of the axial flow fan are various. The axial flow fans are often used under unsuitable operating condition. Especially, the cases where the obstacles are distributed in upstream of the fan to downsize are increasing, in recent high density design of equipment. An attempt is made to clarify the influence of the obstacle on the flow characteristics of axial-flow fans. In this study, a blockage disk is installed upstream of a test fan which is a typical cooling axial-flow fan. Blockage disks with various diameters are set up. The performance curves of axial-flow fan with blockage disks are measured. In addition, flow instabilities with a cell structure are demonstrated on typical condition. The main objects of the present study are : to evaluate the performance degradation when obstacles are installed in upstream of the test fan, to elucidate causes of positive slope for the performance characteristics curves and reverse flow, to clarify the generation mechanism of flow instabilities when the blockage disks which are larger than diameter of the test fan are installed.

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Indoor and outdoor units of home-use air conditioner incorporate compact fans for heat exchange. Typical forms of these fans are forward type sirocco fan, axial-flow type propeller fan and cross-flow type tangential fan. They are required to be small enough for a given unit size and also to have an appropriate air flow rate, a lower noise level and a higher energy saving (fan efficiency). However, in designing the fan built in a newly developed air conditioner unit, it is generally difficult to satisfy all of required conditions only by similarity law using known parameters of a prototype fan. Therefore, this study aims to offer a modified, semi-empirical similarity law based on experimental data which enables us to give the fan with better efficiency and lower noise, even though the geometrical shapes of each part of the fan may slightly differ from those of the prototype fan.

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For the purpose of balancing axial thrust, balance piston mechanism is often used in rocket engine turbopumps. Balance piston is a self-thrust balancing system and quasi-statically stable, but might become unstable due to a compressibility of liquid hydrogen, one of the major propellants for rockets. In past rocket engine firing tests, the self-induced axial vibration caused by balance piston instability occurred in a liquid hydrogen turbopump. So it is needed to establish the evaluation technique to understand the dynamic characteristics of balance piston mechanism. In this report, axial eigenvalues of balance piston mechanism are studied analytically by one-dimensional model in various ways, and the difference of results due to the difference of analysis methods is discussed.

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In the design for a wind turbine, the validation of the numerical computation result is almost carried out by the comparison with the wind tunnel experiment. However, the Reynolds number of the wind tunnel experiment is low and the flow does not become turbulence fully developed on a leading edge of wind turbine blade. Therefore, the transition area from laminar to turbulence becomes wide under the conditions, and the separation point is difficult to predict using the turbulence models. The prediction precision extremely decreases in the tip speed ratios less than a maximum power point. This study carries out the unsteady calculation without and with turbulence models for a 3-blades horizontal axis wind turbine. The validation of the calculations is performed by comparing with the experimental results. The power coefficients calculated without turbulence models are in agreement with the experimental data for the high tip speed ratio heiger than 5.

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In order to discuss the major factor on the noise characteristics of a propeller fan, the influence of the blade numbers on the periodical fan noise generated due to the blade tip vortex is analyzed. The influence of the blade tip vortex on the fan noise is argued by the measured internal flow. For the analysis of the structure on the mean flow in the blade passage, the phase of the unsteady signal of the wake is locked by the trigger signal synchronized with the rotation signal. The noise generated from the tip vortex became 200 Hz even if the number of blades was different. We clarified experimentally that the periodical noise due to the blade tip vortex changed according to the scale of the tip vortex.

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