隨著科技的進步，消費型電子產品皆往短小輕薄方向發展，因此組成元件隨之縮小以便置入更小體積中，其中包括散熱系統及冷卻風扇等；而縮小後的風扇須提高轉速，才能產生足夠冷卻氣流，也因此衍生了惱人之氣動噪音。為了抑制此氣動噪音，本研究選用亥姆霍茲共振器來進行離心扇之窄頻帶噪音的降噪，利用不同設計參數分析探討相對應之效果。首先利用CFD模擬軟體進行前傾式離心扇的優化設計，藉由更動風扇尺寸、出口造型、葉片出入口角、葉片數及出口導葉等參數，完成優化設計並將之作為基準風扇；接著經由計算結果探討流場與噪音之連動關係，試圖找出風扇的最大噪音源，且將共振器裝於最大噪音源進行降噪。隨後針對此具有共振器之風扇進行流場與噪音的數值模擬，以確認共振器應用於風扇的降噪效果；同時，製作共振器及風扇原型，並組裝成風扇進行相關性能實驗，透過量測結果來驗證數值模擬之準確度。由裝配亥姆霍茲共振器的風扇實驗可得知，共振器對風扇之氣動性能影響不大，而降噪效果最高可降特徵頻率之噪音3.9dB；透過與模擬的結果比較，模擬和實驗所得之特徵頻率的降噪趨勢相同。綜合歸納上述結論，本文所探討的亥姆霍茲共振器應用於離心扇確實有效果，但應針對共振器之設計參數和安裝位置作更多探討，才能確保此減噪方案之實用性。

With the advancement of science and technology, consumer electronics have developed to be shorter and thinner. Therefore, the size of their components and circuit boards are reduced to fit in smaller spaces. These components include fans and cooling systems, and in order to provide equivalent fan performance, the fan speed increases to provide the fan performance required for the cooling system, leading to aerodynamic noises. In order to suppress the aerodynamic noise mentioned above, the resonator is introduced into the study of noise reduction. However, the volume of the λ/4 resonator is too large to be installed into electronics; so as to overcome this difficulty, this study will use the Helmholtz resonator to conduct the noise reduction of the narrow-band noise of the centrifugal fan, and different resonator designs to study the noise reduction application of Helmholtz resonance.
First, the CFD simulation software is used to design the forward curved centrifugal fan. The design is completed by changing the size of the fan, the shape of the fan outlet , the number of impeller blades , and the guiding vane . As a reference fan , the forward curved centrifugal fan is used to investigate and understand the linkage relationship between its flow field and its noise, so as to find the biggest noise source of the fan, where the Helmholtz resonator is installed for noise reduction. Then, the numerical simulation of the flow field and the noise of the fan with the resonator is carried out, from which the result will determine the fan’s effect on noise reduction. Meanwhile, the resonator and the impeller and shell of the fan are made with the SLA processing technology, then put to related performance experiments with the reference fan. The measurement results are used to verify the accuracy of the numerical simulation.
According to the experiment of the Helmholtz resonator-installed fan, it can reduce up to 3.9dB of the 1st BPF . When comparing the simulation results, while there are some inaccuracy in the simulation and experiment, the results concerning the characteristic frequency have shown a similar trend in the simulated noise reduction. The application of the Helmholtz resonator on centrifugal fans discussed in this paper indeed shows high effectiveness and adaptability. After the completion of this system, it can be provided for the industry as a reference.

參考文獻
[1] Eck, B., “Fans : Design and Operation of Centrifugal, Axial-Flow and Cross-Flow Fans”, Pergamon Press, New York, 1973.
[2] Bowerman, R. and Acosta, A., “Effect of the Volume on Performance of a Centrifugal Pump Impeller,” Trans. ASME, Vol. 79, pp. 1057-1069, 1957.
[3] Leidel, W., “Einfluss Von Zungenabstand and Zungenradius auf Kennlinie und Gerausch eines Radial Ventilators ,” DLR-FB, pp. 61-69, 1969.
[4] Raj, D. and Swim, W. B., ”Measurements of the Mean Flow Velocity and Velocity Fluctuations at the Exit of an F-C Centrifugal Fan Rotor,” Journal of Engineering for Power, Vol. 103, pp. 393-399, 1981.
[5] Lin, S. C., “A Novel F-C Centrifugal Fan Design for Improved Performance,” Department of Mechanical Engineering, Technical Report, Tennessee Technological University, 1982.
[6] 吳慶財，“前傾式離心扇之實驗設計”，國立台灣工業技術學院機械工程技術研究所碩士論文，1993年。
[7] Huang, J., Yin, M., and Yao, X. J., “Effects of Concealed Motor’s Shape on Performance of Forward Multi-Blade Centrifugal Fans,” Journal of Shanghai Jiaotong University, Vol. 35, No. 8, pp. 1196-1199, 2001.
[8] 黃家烈，“筆記型電腦冷卻風扇之研究”， 國立台灣科技大學機械工程技術研究所博士論文，2001 年。
[9] Zeller, W. and Stang, H., “Predetermination of the Axial-Flow Fans,” Heizung-Luftung-Haustchnik, Vol. 9, No. 12, pp. 995-1054, 1957.
[10] Zeller, W., “Conerning Mathematical Treatment of Noise Behaviour in Fans for Air Conditioning Plants,” VID-Berichte, No. 38, pp. 695-708, 1959.
[11] Schlichting, H., “Application of the Boundary Layer Theory to Flow Problems of Turbo Machines,” Siemens-Zeitschrift, Vol. 33, No. 7, pp. 74-82, 1959.
[12] Neise, W., “Noise Reduction in Centrifugal Fans: a Literature Survey,” Journal of Sound and Viberation, Vol. 45, No. 3, pp. 375-403, 1976.
[13] Alster, M., “Improved Calculation of Resonant Frequencies of Helmhlotz Resonantors,” Journal of Sound and Vibration, Vol. 24, No. 1, pp. 63-65,1972.
[14] Beranck, L., “Noise and Vibration Control,” Institute of Noise Control Engineereering, Washington, DC, 1998.
[15] Parente, C. A., “Hybird Active/Passive Jet Engine Noise Suppression Systems, ” NASA CR-1999-208875, NSL-RPT-98-002, February, 1999.
[16] Han, S. H., “Sound reduction by a Helmholtz resonator,” Master Thesis , The Department ofMechanical Engineering and Mechanics, Lehigh University, 2008.
[17] Han, S. S. and Rhim, Y. C., “Noise-Level Reduction of a Slim-Type Optical Disk Drive Using the Idea of a Helmholtz Resonator ”, Transactions on Magnetics, Vol. 45, No.5 , pp. 2217-2220, 2009.
[18] 陳彥彰，“亥姆霍茲共振器應用於管路風機之實驗與模擬整合研究” ，國立台灣科技大學機械工程技術研究所碩士論文，119-136頁，中華民國一零三年。
[19] Zhao Xiao-Dan, “Improving Low-Frequency Sound Absorption of Micro-Perforated Panel Absorbers by Using Mechanical Impedance Plate Combined with Helmholtz Resonators,” Master Thesis , School of Automobile and Traffic Engineering , Jiangsu University, 2016.
[20] Cai, Chenzhi, “An Extended Neck Versus a Spiral Neck of the Helmholtz Resonator,” Master Thesis, Department of Building Services Engineering, The Hong Kong Polytechnic University, 2016.
[21] Neise, W. and Koopman, G. H., “Reduction of Centrifugal Fan Noise by Use of Resonator,” Journal of Sound and Viberation, Vol. 72, No. 2, pp. 297-308,1980.
[22] 洪宗揚，“後傾式離心風機之噪音研究”，國立台灣工業技術學院碩士論文，1996年。
[23] 呂水煙, “前傾式離心風機之噪音研究”，國立台灣工業技術學院碩士論文, 1997年。
[24] 吳御銓，“λ/4減噪器應用在離心扇之數值與實務整合研究”，國立台灣科技大學機械工程技術研究所碩士論文，127-130頁，中華民國一零三年。
[25] Lighthill, M. J., “On Sound Generation Aerodynamically-I. General Theory,” Proc. Roy. Soc., London 211, pp. 564-587, 1952.
[26] 黃家烈、簡宏斌，“軸流風扇之數值模擬與實驗分析”，中華民國「航太學會/燃燒學會/民航學會」航太聯合會議，桃園，107-117頁，中華民國八十八年。
[27] 黃家烈、許豐麟，“進風口面積在新式筆記型電腦冷卻扇之研究”，中華民國機械工程學會第十七屆全國學術研討會論文集，高雄，中華民國八十九年。
[28] 游裕傑，“離心式電腦風扇的設計與分析”，國立成功大學機械工程學系碩士論文集，2002 年。
[29] 周志成，“新型離心式風扇數值與實驗整合研究”，國立台灣科技大學機械工程技術研究所碩士論文，134-149頁，中華民國九十五年。
[30] 尤清，“無扇葉風扇之數值與實驗整合研究”，國立台灣科技大學機械工程技術研究所碩士論文，126-165頁，中華民國一零三年。
[31] Lowson, M. V., “The Sound Field for Singularities in Motion,” Proceedings of the Royal Society of London, pp. 559-572,1965.
[32] Rafael, B. T., Sandra, V. S., Juan Pablo, H. C., and Carlos, S. M., “Numerical Calculation of Pressure Fluctuations in the Volute of a Centrifugal Fan,” Journal of Fluids Engineering, Vol. 128, pp. 359-369, 2006.
[33] Liu, Q., Qi, D., and Mao, Y., “Numerical Calculation of Centrifugal Fan Noise,” Proceedings of Mechanical Engineers. Part C, Journal of Mechanical Engineering Science, Vol. 220, pp. 1167-1177, 2006.
[34] Lu, H. Z., Huang, L., So, R. M. C. and Wang, J., “A Computational Study of the Interaction Noise from a Small Axial-Flow Fan,” Journal of the Acoustical Society of America, Vol. 122, pp. 1404-1415, 2007.
[35] 蔡明倫, “風扇性能評估與設計方法之整合研究”，國立台灣科技大學博士論文, 2010年。
[36] 《西京雜記》卷一：「長安巧工丁緩者……又作七輪扇，連七輪，大皆徑丈，相連續，一人運之，滿堂寒顫。」
[37] Bleier, Frank P., “Fan Handbook: Selection, Application, and Design,” McGraw Hill, 1997.
[38] Morinushi, K., “The Influence of Geometric Parameters on F. C. Centrifugal Fan Noise,” Journal of Vibration, Acoustics, Stress and Reliability in Design, Vol. 109, pp. 227-234, 1987.
[39] Kondo, L. and Aoki, Y., “Noise Reduction in Turbo Fans for Air Conditioners,” Technical Review-Mitsubishi Heavy Industries, Vol. 26, No. 3, pp. 173-179, 1989.
[40] CNS 8753, Determination of Sound Power Level of Noises for Fan, Blower, and Compressors, Chinese National Standard, 1982.
[41] Hermholtz Resonator – Research on Materials and Thier Resonate Qualities, https://clareandreallo.wordpress.com/2011/05/30/hermholtz-resonator-research-on-materials-and-thier-resonate-qualities/
[42] Wikipedia http://en.wikipedia.org/wiki/Helmholtz_resonance
[43] Patankar, S. V. and Spalding, D. B., “A Calculation Procedure for Heat Mass and Momentum Transfer in Three-Dimensional Parabolic Flows,” International Journal of Heat Mass Transfer, Vol. 15, pp. 1787-1806,1972.
[44] Launder, B. E. and Spalding, D. B., “Lectures in Mathematical Models of Turbulence,” Academic Press, London, England, 1972.
[45] Ffowcs Williams, J. E. and Hawkings, D. L., “Sound Generation by Turbulence and Surface in Arbitrary Motion,” Philosophical Transactions of the Royal Society of London, Vol. 264, pp. 321-342,1969.
[46] 李宗穎，“筆記型電腦散熱模組之數值與實驗整合研究”，國立台灣科技大學機械工程技術研究所碩士論文，96-106頁，2006年。