Design optimization have become widely used in industry fields as a means of improving aerodynamic performance while satisfying various design constraints. Adjoint method, which can calculate the sensitivity of the objective improvement to shape changes by only one calculation, has been adapted gradient-based optimizations to reduce the calculation cost. In this study, single-point and multi-points gradient-based optimizations using adjoint method were conducted for a centrifugal compressor impeller in order to improve aerodynamic performance. As theses optimizations results, the peak efficiency was improved by 3.5％ in the single objective optimization. In the multi-objective optimization, the operating point efficiency was improved in wide area while maintaining the same mass flow capacity as the baseline.

Contra-rotating rotors are suitable for a small hydroturbine, because they can be expected to achieve compactification of radial direction and high performance. However, a conventional contra-rotating rotor is composed of two axial flow rotors, so it has a specification suitable for high flow rate and low head. In order to achieve a small hydroturbine suitable for low flow rate and high head, we propose a new type of contra-rotating rotor, which is composed of a hybrid rotor and a centrifugal rotor. We investigated the performance of this hydroturbine by experiment and numerical analysis. As a result, it became clear that the performance of the rear rotor was low. And we considered the cause from the internal flow conditions.

A fundamental model of air column resonant surge is proposed. It is assumed that the flow in the suction pipe is incompressible but the effects of compressibility and pipe resistance are taken into account in the discharge pipe. The characteristic equation is derived and the differences of onset condition and frequency from those of Helmholtz resonant surge are discussed. The results are validated by comparisons with experiments.

The development of wind power generation from large wind turbines has shown excellent profitability, however, large wind turbines must be built in locations away from residential area, from the point of view of the landscape and noise. Wind power generation also requires that wind conditions be good and the site be near an electric power-consuming region. A Magnus wind turbine which uses a rotating cylinder as a substitution for the blade of a common wind turbine. The Magnus wind turbine is compact, resistant to wind pulsation and can be installed in residential areas. The purpose of this study is to optimize the shape of the straight fin attached to a rotating cylinder by using genetic algorithms and CFD, in order to improve lift-to-drag（L/D）ratio under the low rotating speed conditions. The validity of the CFD is confirmed by comparing the results in a wind tunnel experiment. The proposed new straight fin attains the lift enhancement and the drag reduction in contrast to the original straight fin at low rotating speed of the cylinder.

The present paper focuses on effect of flow and hole cross-sectional shape on acoustic absorption performance of perforated plate with background air space. We experimentally measured the flow rate, acoustic pressure, and transfer function using the improved acoustic impedance tube. The normal incidence absorption coefficient was calculated from the measured transfer function using transfer function methods. As the bias flow velocity passing through the orifices increased, the peak level of the acoustic absorption coefficient increased. The acoustic absorption performance has improved using taper orifices of perforated plate. The peak frequency of the acoustic absorption coefficient depended on the taper angle of hole of perforated plate. Velocity measurements were performed around perforated plate by means of particle image velocimetry. The vortices were formed clearly at the downstream of the orifices due to incident sound of pure tone. We discussed the relation between flow field and acoustic absorption performance of perforated plate with bias flow.

The tumbling is one of autorotations, and can be used for a novel windmill and waterwheel. The authors conduct a series of subsonic wind-tunnel experiments with the least support-friction loss, in order to investigate the effect of cross-section geometry upon the tumbling of a simple two-dimensional rectangular-cross-section prism. On the basis of the freely-rotating rate of the prism, the tumbling can be classified into two; namely, a flat-plates mode for depth-to-width ratio λ<0.6 with reduced rotating rate Ω^*_max≃0.4-0.6, and a rectangular-prism mode for λ≥0.6 with Ω^*_max≃0.4. In the former mode, Ω^*_max monotonically decreases with increasing λ.