スリットを有するケーシング内の小型軸流ファンの性能・発生音の測定

抄録

A small axial-flow fan utilized in cooling systems of electronic equipment is often installed in a casing with slit structures. However, in some installation conditions, the ventilation through the slits is prevented due to obstructions. In this study, the effects of slit structures of the casing on performance and aerodynamic sound were investigated. The fan with casings of different slit intervals were installed in a rectangular duct. When the casing slit was completely blocked, the pneumatic power by the fan was decreased around a design flow rate. The results of numerical simulations performed along with the experiments indicated that the flow towards the tip of each blade appears for the casing without slit structures, where the flow separation occurs at the leading edge of the blade and the wake becomes more turbulent. The experiments showed that the velocity fluctuations measured between the blades and struts are intensified in broadband frequency range by the turbulence in the wake. Also, the measured sound pressure levels at the harmonic frequencies of the blade passing frequency (BPF) were lower and the broadband level was higher for the casing without slits than for the casing with slits, respectively. The power of the velocity fluctuations at BPF and harmonic frequencies in the wake was found to be also decreased by closing slits. In addition, the experimental results with a different slit interval showed that the sound pressure levels at the harmonic frequencies can be reduced with the appropriate slit interval while preventing the performance degradation.