In this study, the generation mechanism of the discrete frequency noise from a small axial flow fan having an outlet guide vane was analyzed based on the wake characteristics of the rotor blades. Based on the organize of the actual measured fan noise, we indicated that the noise in the vicinity of the design point of the fan with the outlet guide vanes was affected by the discrete frequency noise synchronized with the blade passing frequency. The drag force formed in the wake near the blade tip represented the characteristics of the discrete frequency noise. We clarified that the discrete frequency noise of the small axial fan was generated by the drag force formed at the blade tip flowing into the outlet guide vanes.

Centrifugal pumps designed for operation at low flow rates used in various applications such as medical, food processing, chemical, and manufacturing are known to be less efficient than general industrial pumps. To overcome this problem, small double-rotating single screw pump was developed based on the principle of a single-screw pump. The pump mainly consists of a rotor, stator, and casing, with the stator rotating passively as the rotor rotates. Therefore, there are two very narrow gaps between the rotor and the stator, and between the stator and the casing, where the differential pressure inside the pump causes leakage. In this report, improvement of pump efficiency by filling the gap between the stator and the casing with grease to reduce leakage loss was investigated.

A centrifugal compressor used in turbochargers, industrial compressors and so on consists of an impeller, which is a rotating part, and a diffuser and a scroll, which are stationary parts. The kinetic energy given to the fluid by the impeller is decelerated and converted to pressure in the diffuser, then collected circumferentially by the scroll, and guided to the discharge pipe finally. In order to improve the aerodynamic performance of centrifugal compressors, the scroll is designed to minimize its pressure loss and also to prevent non-uniform circumferential pressure distribution to suppress the influence on the impeller and diffuser. As a result, the centrifugal compressor scroll has a cross-sectional area distribution which is gradually increased in the circumferential direction toward discharge. However, it is well-known that the off-design performance is deteriorated significantly due to the mismatch of the flow distribution and the area distribution of the scroll. In this study, to clarify a variation of flow distribution in the compressor scroll at the off-design condition, traverse measurements using a 5-hole yaw meter probe were conducted on two types of scrolls with different cross-sectional area and shapes, and the internal flow of the scrolls were investigated in detail when the pressure ratio and flow rate are changed.

Ducts are widely used in an industry field. For example, a high-power suction truck has a complex piping system which starts from a root blower to a final exit while repeating bend. The root blower generates a large pulsation and make resonance with the piping system. In order to avoid the resonance, it is necessary to know the natural acoustic frequency of the piping system. We already reported on the resonant frequency of sound fields in ducts with different diameters. This paper investigates the noise damping effects of bending in ducts with multiple bends. Additionally, the noise damping effects of inserting sound-absorbing materials into the duct were also examined. Through experiments and analysis, the frequencies at which damping effects occur were identified. Furthermore, it became clear that the frequencies at which damping effects occur vary depending on the inner diameter of the duct.