中文摘要
風扇是散熱技術中一種相當主流且成熟的對策，產生的振動卻會讓人感到不舒服及加入系統後對組合件產生種種不良的影響，例如：當機或結構損壞，小振動也有可能造成共振放大。
本研究的內容是解決40*40*48mm尺寸的風扇因共振所產生的振動問題，針對風扇的結構進行自然頻率的模擬，再配合實驗測得的自然頻率進行比對，結果是模擬與實驗結果相符，為解決共振造成的振動問題，採用改變結構設計的方式改變自然頻率，發現自然頻率僅由3000Hz拉到3200Hz。因而採取改變風扇葉片數及轉速的方式，使振動源的頻率避開自然頻率，再用流場模擬來比對看數據是否合理，結果是實驗與結果相符，並非一定葉片多性能就會好，從模擬的結果也可以佐證實驗結果無誤，最後葉片數由7（入風）/4（出風）葉改成5（入風）/4（出風）葉匹配，轉速也由14500rpm改成15500/11600rpm。本研究發現利用流場分析的方法將扇葉轉速改變對減少共振及避開振動頻率是有效的，再以此風扇施以衝擊試驗，得知此設計對風扇整體抗衝擊的能力在設計改變前後沒有明顯差異。
風扇的架構在初步設計後大多已經定型，除非有大的設計變更，自然頻率是不會有太大的改變，期待只藉由改變結構的共振頻率避免激振，是難以達到預期效果的，還得配合上其它對策才能確保產品振動的穩定性。

ABSTRACT
Fan cooling is a fairly mainstream and well-developed technology. Vibration may make users feel uncomfortable. Assembly system may produce different noises right after the adverse effect components were destroyed, such as computer crashed or vibration or fan structural damage subsequently affects their fan reliability. Therefore, small vibration resonance amplification can not be overlooked.
The researcher applied a 40 * 40 * 48mm fan to solve the problem of resonant vibration. He found the similar results of the natural frequencies of the structure of the fan by experimental and finite element analysis. In order to improve the vibration resonance, he changed the structural of the fans. In different structural designs, the natural frequencies did not change a lot. The natural frequency switched from 3000Hz to 3200Hz. To avoid the resonant frequency of the assemble fan, the researcher changed the number of fan blades and simulated the flow field. Compared the data to the experimental results, the results of the analysis were reasonable. The results showed the performance of the assembly fan did not necessarily need more leaves. The leaf numbers were from 7 (Inlet Fan) & 4 (Outlet Fan) into 5 (Inlet Fan) & 4 (Outlet Fan). Operation speed was changed from 14500 rpm (Inlet & Outlet Fan) to 15500 rpm (Inlet Fan) &11600 rpm (Outlet Fan). Using the fluid flow analysis, he found the change of the leaf number and operation speed of the fan could effectively avoid the resonance frequency and reduce vibration. An impact analysis was also helped to verify the capacity of the anti-impact of the fan.
The structure of the fan after the preliminary design has been shaped mostly. By only changing the structural design to avoid excitation of the resonant frequency is difficult to achieve the effective function. To ensure the product stability, it is necessary to deal with the inducing vibration of the fluid flow.

目錄
誌謝 i
中文摘要 iii
ABSTRACT iv
目錄 v
表目錄 vii
圖目錄 viii
符號表 xi

第一章 緒論 1
1.1 前言 1
1.2 簡介 1
1.3 研究動機與目的 5
1.4 參考文獻 7
第二章 風扇設計參數 10
2.1 模態理論 10
2.2 衝擊理論 12
2.3 流場理論 15
2.3.1 紊流模式 16
2.3.2 standard k-ε模型 16
2.3.3 RNG k-ε模型 18
第三章 試驗方式與設備 20
3.1 動平衡試驗 20
3.2 風扇運轉振動頻譜測試 24
3.3 模態測試分析比對 27
3.4 風量風壓測試機 28
第四章 試驗與糢擬數值比對 31
4.1 試驗進行方向 34
4.2 模態問題分析 35
4.2.1 完整模型的模態模擬結果與激振錘敲出結果比對 36
4.2.2 模型簡化與邊界條件設定 36
4.3 改變風扇的條件觀察對模態的影響 36
4.3.1 增加雙風扇的結合預力 40
4.3.2 改變扇葉材質 42
4.3.3 變更彈簧預壓力 43
4.3.4 變更扇葉片數 43
4.3.5 觀察零件組合前後與風扇的關係 44
4.4 流場問題分析 49
4.5 分析加入結合預壓力前後衝擊應力的變化 55
第五章 結論 58
參考文獻 60

參考文獻
[1] Rahman, B. S., and Lieu, D. K., 1991, “The Origin of Permanent Magnet Induced Vibration in Electric Machines,” Journal of Vibration and Acoustics, Vol.113, pp.476-481.
[2] Ding, J. J., Jumaily, A. Al., 2000, “A Linear Regression Model for the Identification of Unbalanced Changes in Rotating Machines,” Journal of Sound and Vibration, Vol.231, No.1, pp.124-144.
[3] 陳浩然，2002，磁碟陣列機之振動分析，元智大學碩士論文，頁10-30。
[4] 陳永樹，張成，王慶順，2002，風扇外殼結構動態特性分析與設計，中華民國第二十六屆全國力學會議，虎尾，論文編號：D030。
[5] 呂彥達，2003，個人防護衣設計及其循環風扇之流場和振動分析，崑山科技大學，頁87-116。
[6] 林國楨，1991，汽車引擎冷卻風扇設計發展，機械工業雜誌，頁204-214。
[7] 張瑞釗、許忠福、施良磷、張起領，1986，渦輪葉片參數設計法，中山科學研究院，第一研究所研究報告。
[8] William C., Osborne, 1977, “FANS”, Pergamon Press, New York.
[9] Eck, B., 1973, “Fans: Design and Operation of Centrifugal, Axial-Flow and Cross-Flow Fans”, Pergamon Press, New York.
[10] Shepherd, D. G., 1956, “Principles of Turbomachinery”, Macmillan Publishing Co., Inc., New York.
[11] S.C. Morris,JJ. Good,J.F. Foss,，1998，“Velocity Measure in the Wake of an Automotive Cooling Fan, Experimental Thermal and Fluid Science”,pp:100-106.
[12] M.G. Beiler,T.H., 1999, “Compuation and Measurement of the Flow in Axial Flow Fans with Skewed Blades,Journal of Turbomachinery, vol. 121”, pp:59-66.
[13] H.J. Myung, J.H. Baek, 1999, “Mean Velocity Characteristic Behind a Forward-Swept Axial Flow Fan”, JSME International Journal, Series B, 42(3), pp: 476-488.
[14] E.E. Elhadi, Keqi. Wu, 2002, “Simulation of Vortex Flows in Axial Flow Fan Using Computational Fluid Dynamics,” Pakistan Journal of Information and Technology, 1(3), pp: 242-249.
[15] J. Prato, B. Lakshminarayana, N. Suryavamshi, 2001, “Three-dimensional flow field downstream of an embedded stator in a multistage axial flow compressor. Part 1: Steady and Unsteady flow fields, Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, 215(3),” pp: 281-299.
[16] N.Suryavamshi, B. Lakshminarayana, J. Prato, 2001, “Three-dimensional flow field downstreamm of an embedded stator in a multistage axial flow compressor. Part 2: Deterministic stress and heat flux distribution and average-passage equation system, Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, 215(3),” pp: 301-322.
[17] J. Tallman, B. Lakshminarayana, 2001,“Numerical simulation of tip leakage flows in axial flow turbines with emphasis on flow physics: Part 1-Effect of tip clearance height, Journal of Turbomachinery”, 123(2), pp: 314-323.
[18] J. Tallman, B. Lakshminarayana,“Numerical simulation of tip leakage flows in axial flow turbines with emphasis on flow physics: Part 2-Effect of outer casing relative motion, Journal of Turbomachinery, 123(2) ”, pp:324-333.
[19] X. Xiao, A.A. McCarter, B. Lakshminarayana,，2001，“Tip clearance effects in a turbine rotor Part 1-Pressure field and loss, Journal of Turbomachinery, 123(2)”, pp:296-304.
[20] 張裕慶，1997，軸流風扇之數值模擬，台灣科技大學碩士論文.
[21] W.W. Copenhaver, E.R. Mayhew, C. Hah, A.R. Wadia, 1996, “ The Effect of Tip Clearance on a Sweep Transonic Compressor Rotor, ” ASME Journal of Turbomachinery, pp: 230-239.
[22] Fukano, T., Takamatsu, Y. and Kodama, Y., 1986, “The effects of Tip Clearance on the Noise of Low Pressure Axial and Mixed Flow Fans,” Journal of Sound and Vibration, Vol. 105, No. 2”, pp. 291-308.
[23] 王栢村，1994，振動學，頁2.1-2.57.
[24] 陳精一，2006，Ansys振動實務分析，頁187-420.
[25] Robert W. Fox,Alan T.McDonald ，2004，流體力學（第五版）Indruction to Fluid Mechanics.
[26] 丁明岳，G Tech動平衡機使用手冊。
[27] J. Estevadeordal a, S.Gogineni a, W. Copenhaver b, G. Bloch b, M. Brendel, 2000, “Flow Feld in a low-speed axial fan: a DPIV investigation,” Experimental Thermal and Fluid Science 23.