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A Study on the Process of Low-Frequency Noise Generation in A Multi-Blade Centrifugal Fan
Masatoshi Kawasaki,Hiroyuki Hirahara,Donghyuk Kang 한국유체기계학회 2020 International journal of fluid machinery and syste Vol.13 No.2
This study numerically investigates the flow characteristics of a multi-blade centrifugal fan in order to identify the process of low-frequency aerodynamic noise generation. Computational analysis has been carried out using the large eddy simulation (LES) model. In the preliminary study, it was confirmed that the present computational fluid dynamics simulation using LES shows good agreement with the experimental results of the performance curve, sound pressure spectra, and the flow field obtained by using a time-resolved particle image velocimetry (PIV) system. Consequently, it was found that the appearance of an unexpected significant flow, which recirculated from the scroll casing, passed through the impeller, and returned to the scroll casing again to exit the scroll casing in a specific region, was similar to the flow suggested in the experimental results, which were obtained utilizing PIV measurement. The fluid flow related to the fluctuation, which was remarkably not included in the impeller main flow, existed beside the outer main flow. A certain amount of fluctuated flow bifurcated near the scroll end, one regurgitating into the impeller, and another colliding with the tongue. The former became a driving source of noise and the latter a direct noise-generating factor. Consequently, it was demonstrated that a significant fluctuation owing to flow collision with the tongue propagated through the impeller and formed a loop.
PIV measurement of oscillatory flow in a micro-channel as a bronchiole model
Won-je LEE,Massaki KAWAHASHI,Hiroyuki HIRAHARA 한국가시화정보학회 2004 KOREA-JAPAN Joint Seminar on Particle Image Veloci Vol.- No.-
The improvement of artificial respiration method has brought about the decrease in mortality of pulmonary diseases patients. Various respiratory curative methods, inclusive of HFOV (High Frequency Oscillatory Ventilation), have been developed for more effectual and less harmful management of acute respiratory failure. However, the mechanism of gas transfer and diffusion in a bronchiole has not yet been clarified in detail. As a first approach to the problem, we measured oscillatory flows in a Y-shaped micro-channels as bronchiole model by micro Particle Image Velocimetry(micro PIV). In order to establish the fundamental technique of PIV measurements on oscillatory air flow in a micro-channel, we used about 500-㎚ -diameter incense smoke particles, a diode laser, a high speed camera including an objective lens, and a HFOV, which is effective technique for medical care of pulmonary disease patients, especially, infants. The bronchiole model size is that parent tube is 500㎛ width and 500㎛ depth, and daughter tubes are 450㎛ width and 500㎛ depth. From this study made on the phenomenon of fluid in micro size bronchus branch of a lung, we succeeded to get time series velocity distribution in a micro scale bronchial mode. The experimental results of velocity distribution changing with time obtained by micro PIV can give fundamental knowledge on oscillatory airflow in micro-channel.