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Experimental Research for Performance and Noise of Small Axial Fan
Ito, Takahiro,Minorikawa, Gaku,Fan, Qinyin Korean Society for Fluid machinery 2009 International journal of fluid machinery and syste Vol.2 No.2
Small axial fans have become widely used as cooling devices in recent years. Because of their increasing importance, studies have been conducted on ways to improve the performance and reduce the noise of such fans. In this report, a small axial fan with a diameter of 85 mm (a type popularity used in personal computer or workstation) was selected for further examination. The influence on aerodynamic performance and noise of such frame design parameters as blade tip clearance results in a decrease of discrete frequency noise and an increase of broad-spectrum noise. As for the most suitable design refinement in terms of fan efficiency, we found that the treatment of outlet corner roundness and altering spoke skew to the direction counter to that of fan rotation was effective.
임태균,전완호,Gaku Minorikawa 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.11
This study is an attempt to characterize unsteady flow field and predict flow noise produced by a radial fan installed in a system that has a tiny gap between the fan casing and upper wall (similar conditions found in actual products). The large-eddy simulation turbulence model was used to simulate unsteady flow conditions, and an impeller was rotated 13 times in total to sufficiently develop unsteady flow and obtain data for Computational aeroacoustics (CAA). Unsteady flow field due to the radial fan structure and narrow flow channel in a system was verified, and a location wherein flow properties rapidly changed over time due to the complicated flow field was identified. The noise spectrum obtained through CAA was compared with that measured through experiment. Both tonal noise components consisting of blade passing frequency with its harmonic frequencies and broadband noise were matched. The major source of noise of the radial fan was on the inner surface of the casing. However, the sources of noise in the upper and lower sides of the casing were not equivalent to each other due to the interaction between the flow coming through an inlet located in the upper part of the casing and the flow discharged through an outlet installed at its side, as well as the interaction between impeller rotation and cut-off. Sources of noise located at the upper casing are caused by the flow around impeller tips, whereas sources on the lower casing are related to the interaction of the flow between the impeller and casing. A low noise model with a modified impeller tip was proposed, and its noise reducing effects were evaluated. The modified model reduced overall sound pressure level by 0.8 dB compared with the base model.
Design and Prototyping Micro Centrifugal Compressor for Ultra Micro Gas Turbine
Hirano, Toshiyuki,Tsujita, Hoshio,Gu, Ronglei,Minorikawa, Gaku Korean Society for Fluid machinery 2009 International journal of fluid machinery and syste Vol.2 No.4
In order to investigate the design method for a micro centrifugal compressor, which is the most important component of an ultra micro gas turbine, an impeller having the outer diameter of 20mm was designed, manufactured and tested. The designed rotational speed is 500,000 rpm and the impeller has a fully 3-dimensional shape. The impeller was rotated at 250,000 rpm in the present study. The experimental results of the tested compressor with the vaned and the vaneless diffusers were compared. It was found that the vaned diffuser attained the higher flow rate than the vaneless diffuser at the maximum pressure ratio. In addition the maximum pressure ratio was higher for the diffuser having a larger diffuser divergence angle at the high flow rate. These results were compared with those obtained by the prediction method used at the design stage.
Tae-Gyun Lim,Wan-Ho Jeon,Gaku Minorikawa 한국유체기계학회 2018 International journal of fluid machinery and syste Vol.11 No.2
In this study, computational fluid dynamics (CFD) and computational aeroacoustics (CAA) were used to reduce the noise of a small axial cooling fan that is widely applied to electronic devices. The noise of an axial cooling fan that was measured in semi-anechoic room was compared with the results obtained from CAA. Three-dimensional Navier-Stokes equations were solved for the unsteady flow field simulation. The noise was calculated by using simplified Ffowcs Williams and Hawkings (FW-H) equation. The result of CAA was consistent with one data obtained from the experiment. The results of unsteady flow field presented the noise generation mechanism and that of CAA presented the sound sources. The shape of a shroud was a factor causing one of the major noise sources on the fan surface. The shape modification was made in the inlet of the shroud for noise reduction. The Overall Sound Pressure Level (OASPL) was reduced by 3.7 dB compared to that predicted for Base model.
임태균,Wan-Ho Jeon,Gaku Minorikawa 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.10
The recent development of small and lightweight rack mount servers and computers has resulted in the decrease of the size of cooling fans. However, internal fans still need to achieve a high performance to release the heat generated from interior parts, and they should emit low noise. On the contrary, measurement data, such as flow properties and flow visualizations, cannot be obtained easily when cooling fans are small. Thus, a numerical analysis approach is necessary for the performance evaluation and noise reduction of small cooling fans. In this study, the noise of a small cooling fan used for computers or servers was measured and then compared with the aeroacoustic noise result based on a numerical analysis. Three-dimensional Navier-Stokes equations were solved to predict the unsteady flow field and surface pressure fluctuation according to the blades and casing surface used. The simplified Ffowcs Williams and Hawkings equation was used to predict aeroacoustic noise by assuming that a dipole is the major cause of fan noise. Results of the aeroacoustic noise analysis agreed well with that of the experiment, and a tonal noise whose frequency was lower than the first blade passing frequency could be identified in the noise spectrum. This phenomenon is caused by the shape of the bell mouth. A coherence analysis was performed to examine the correlation between the shape of the cooling fan and the noise.
축류팬의 유동소음 정확도 향상을 위한 수치해석에 관한 연구
전완호(Wan-Ho Jeon),임태균(Tae-Gyun Lim),御法川學(Gaku Minorikawa) 한국소음진동공학회 2013 한국소음진동공학회 학술대회논문집 Vol.2013 No.4
The paper describes the prediction method for the unsteady flow field and the aeroacoustic noise of an small axial fan. The prediction method is comprised of various CFD conditions and acoustic analogy by using Ffowcs Williams-Hawkings equation. The diameter of tested axial fan is 170 mm and number of blade is 5. Virtual anechoic room which has same size with real one was used for CFD. URANS and LES models were used. For mesh dependence study, a different mesh type was tested and optimized mesh was selected. Calculation conditions were also studied such as time step and turbulence model for accurate noise analysis. In this paper, we got optimum analysis conditions and computational results. The unsteady pressure fluctuation at given 4 points were compared between the measured data and computational results. Also, the predicted acoustic spectrum at 3 given microphone points were compared with measured ones.
Tae-Gyun Lim,Jae Hyuk Jung,Wan-Ho Jeon,주원구,Gaku Minorikawa 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.7
Axial flow fans of outdoor units are equipped with specially shaped winglets and shroud for reduction of the flow-induced noise. In this study, the unsteady state flow field and the characteristics of the flow-induced noise according to the application of the sweptback tip winglets and 30 % covered shroud in an axial flow fan of an outdoor unit of air conditioner were experimentally and numerically analyzed. To analyze the unsteady flow field, large eddy simulation (LES) reflecting the geometry of complicated outdoor unit was performed; and the LES results were used by simplified Ffowcs Williams and Hawkings (FW-H) equation in order to calculate the noise numerically. As a result, asymmetric flow characteristics inside the outdoor unit by the mount and the shape of blade tip and shroud were found to cause inconsistent movement of the tip leakage vortex, which was revealed to change the characteristics of the flow-induced noise.
수치해석기법을 이용한 노트북 소형 냉각팬의 유동 및 소음 특성에 관한 연구
전완호(W.H. Jeon),임태균(T.G. Lim),御法川?(Gaku Minorikawa),宮原雅晴(Masaharu Miyahara) 한국전산유체공학회 2013 한국전산유체공학회 학술대회논문집 Vol.2013 No.10
In recent years, the size of a notebook gets thinner and smaller. Its inner size makes problems in cooling fan performance, system installation condition, and so on. In this study, a small turbofan was installed in the very narrow gap like a notebook system, in order to generate similar condition to a real product. Experiments were performed to measure the fans performance and the flow and noise characteristics, results were compared with computational ones. CFD simulation predicted P-Q curve under about 5% error in high flowrate and its trend agreed with experiment data over the flow range. The noise was measured at a distance of 100 mm from a rotation axis direction of an impeller. The measured data corresponded well with computational ones of broadband and BPF noise analyzed by a commercial program(FlowNoise).