隨著科技進步與雲端產業的發展，主要硬體設備伺服器需應付長時間的運作，其穩定性及可靠度更顯得重要，但伺服器本身結構為狹小的密閉空間，運作過程中所產生的廢熱易使產品效能降低與不穩定的情形；因此風扇在伺服器散熱系統中佔有重要的角色，且因內部阻抗較高，故需要小型高靜壓風扇才能有效地進行系統散熱。本文針對廣泛應用於1U伺服器散熱的4056雙級軸流式風扇，就其設計及參數變化對風扇性能之影響進行討論，首先執行入口風扇設計和流場模擬，並據此建構靜葉式肋條來引導氣流和增加靜壓；分析結果顯示靜葉式肋條之設計，可使流量從22提升至23.25 CFM (5.4%)、靜壓30.76增加至49.51 mmAq (37.9%)，確認此設計能提升風扇氣動力性能此靜葉片係由入口風扇和出口風扇之兩組支撐肋條組成，故並不會增加整體風扇所占空間，而後執行出口風扇設計並串聯成完整之雙級軸流扇。隨後藉流場可視化觀察此風扇整體流場有無缺失，並結合CFD工具作進一步的參數分析，所考量包括葉輪之輪轂外型和毂端比、靜葉肋條數目、和葉片角度參數等，經系統化的參數分析得到最適化的風扇參數組合，以產生足夠的氣動力特性應用於伺服器之散熱系統。
為驗證此最適化雙級風扇之優異性能與模擬可靠性，利用CNC加工與3D列印將此設計模型實體化，以供進行相關的氣動力性能與噪音實測，此測試數據與模擬計算值相互比對；結果顯示兩者的性能曲線之趨勢相當吻合具一致性，可驗證數值模擬的準確和可信度。為了確認最是風扇之優異性能，將實測結果與同規格市售風扇進行比較，在17,000 rpm下結果顯示在噪音值僅差0.6 dBA，其最大流量為34.16 CFM較市售風扇高25.3%、而最大靜壓達66.28 mmAq 較市售風扇高14.5%，且消耗功率僅25.8 W較市售風扇低14%。綜合上述研究成果顯示，最適化風扇能以較低消耗功率產生得到較佳的氣動力性能，此雙級軸流風扇確能滿足1U伺服器或相關產品之散熱需求，同時所建立的風扇設計流程以及參數分析結論，皆可作為後續研究之重要參考。

The high-performance 1U server is used extensively to meet the nonstop-operation requirement for the cloud industry due to its compact size, which becomes a challenging task for thermal engineers. Many heat-generating electronic components are placed closely to form an extremely high system-resistance and heat-density inside this crowded space. Thus, the two-stage 4056 axial fan is developed and utilized to provide the high-pressure sufficient airstream for taking care of this severe thermal situation. Nevertheless, the limited fan space creates serious obstacle to construct a motor delivering sufficient power output to support fan running at near 20,000 rpm. Accordingly, to meet this practical need, this research aims to design a two-stage 4056 axial-flow fan generating an adequate high-pressure cooling air with a superior power efficiency. An integrated CFD and experimental effort is used to carry out the parametric study sequentially over the inlet fan, the supporting frame, and the outlet fan for attaining a superior two-stage 4056 fan. Additionally, the supporting frame ribs of 1st-stage and 2nd-stage fans are assembled to form a complete set of stationary guiding vanes between two counterrotating fans. Thus, under the same limited geometry, the outlet flow of 1st-stage fan can move smoothly into the guiding vane to gain extra static pressure; also, the 2nd-stage fan has a good incoming flow pattern to enlarge the aerodynamic performance of this two-stage axial-flow fan.
At first, under the framework of CFD tool, a systematic parametric study on the impeller is imposed to improve performance of the 1st-stage fan, which is designed with the aids of airfoil and cascade theory. Next, flow simulation is performed to provide the detailed plots for flow visualization, which is useful to construct the appropriate stationary guiding vanes. In addition, the corresponding CFD calculations show that the new guiding frame incorporated with the inlet fan can result a minor flowrate increase (5.4%, from 22 to 23.25 CFM) and a significant pressure gain (37.9%, from 30.76 to 49.51 mmAq). After that, the 2nd-stage fan is optimized with the help of numerical simulation and parametric study, which considers the hub geometry, hub-to-tip ratio, blade angles of rotor, and number of guiding vanes. Thereafter, an optimized two-stage axial-flow fan is obtained by combing the above rotors and frames with the guiding-vane ribs. Moreover, to validate the reliability of CFD prediction, prototype for the best two-stage fan design is manufactured via CNC and 3-D printing technologies for testing its aerodynamic and acoustic characteristics. Consequently, test results show that fan performances attained from CFD and experiment are in great agreement overall. The deviations for all the measured performances are small and within an acceptable range. Furthermore, the test fan performance is compared with that of the commercial fan with same specification. It is found that this designed 4056 fan can generate an extra 25.3% volume flow rate (34.16 CFM), an extra 14.5% static-pressure gain (66.28 mmAq), and a minor bigger noise by 0.5dB, which should be improved after the mass production stage. Additionally, a 14% reduction on power consumption (25.8 W) of this new fan is recorded when it is compared to 29.4W of the reference commercial fan under the same rotation speed (17,000 rpm). In conclusion, this work successfully establishes a systematic scheme to design a superior, effective two-stage 4056 fan for fulfilling the thermal demand of high-end 1U server.

[1]http://www.cc.ntu.edu.tw/chinese/epaper/0008/20090320_8008.htm
[2]https://www.stat.gov.tw/public/data/11281538171.pdf
[3]Zhu, X. C., Lin, W. L., and Du, Z. H., “Experimental and Numerical
Investigation of the Flow Field in the Tip Region of an Axial Ventilation
Fan,” Journal of Fluids Engineering, Vol. 127, pp. 299-307, 2005.
[4]Eck, B., “Fans: Design and Operation of Centrifugal, Axial-Flow, and Cross-
Flow Fans,” Pergamon Press, New York, 1973.
[5]Chen, S. H. and Williams, M. H., “Panel Method for Counter-Rotating Propfans,”
Journal of Propulsion and Power, Vol. 7, No. 4, pp. 593-601, July-August 1991.
[6]Shepherd, D. G., “Principles of Turbomachinery,” Macmillan Publishing CO.,
Inc., New York, 1956.
[7]押田良輝，”送風機技術讀本”，復興出版社，1979年。
[8]Wallis, R. A., “Axial Flow Fans & Ducts,” John Wiley and Sons, Inc., New York,
1983.
[9]Horlock, J. H., “Axial Flow Compressors,” Krieger Pub Co, 1982.
[10]聶能光、李福忠，“風機節能與降噪”，科學出版社，1990年。
[11]簡煥然、施銘銓，“軸流風扇性能測試技術與扇葉技術”，機械工業雜誌，民國八十一年八月，
269-288頁。
[12]施銘銓，“小型冷卻風扇開發介紹”，機械工業雜誌，民國八十四年五月，148-156頁。
[13]Mckenzie, A.B., “Axial Flow Fans and Compressors ,” Published by Ashgate
Publishing Limited, 1997.
[14]Bleier, F. P., “Fan Handbook: Selection, Application,” and Design, McGraw-
Hill, New York, 1998.
[15]Wright, T., “Fluid Machinery: Performance, Analysis, and Design,”
CRC Press, Boca Raton, New York, 1999.
[16]張瑞釗、許福忠、施良璘、張起領，“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，民國七十五年六月。
[17]許文英、陳世雄，“軸流式渦輪葉片參數設計”，中國航空太空學會第三十七界學術研討會論文
集，1995年。
[18]蘇聖斌、陳世雄，“軸流泵葉輪與導葉之設計分析”，中國機械工程學會第十三屆全國學術研討會
論文集，298-306頁，1996年。
[19]林至遠，“軸流風扇的性能提昇與測試”，國立成功大學航空太空研究所碩士論文，1997年。
[20]張裕慶，“軸流風扇之數值模擬”，台灣科技大學機械工程系碩士論文，1997年。
[21]林育洲，“軸流風扇之數值與實驗分析”，國立台灣科技大學機械工程系碩士論文，1998年。
[22]簡宏斌，“PC風扇之三維數值模擬分析”，國立台灣科技大學機械工程系碩士論文，1999年。
[23]林鴻志，“Pentium 4 處理器冷卻風扇之製造與實驗研究”，國立台灣科技大學機械工程系碩士
論文，1999年。
[24]洪國泰，“小型軸流風扇之設計、模擬與實驗整合研究”，國立台灣科技大學機械工程系碩士論
文，2007年。
[25]蔡明倫，”風扇性能評估與設計方法之整合研究”，國立台灣科技大學機械工程技術研究所博士論
文，2010年。
[26]Katagiri, H., Fujikake, K., and Yamada, K., “Automotive Mixed Flow Fan with
Guide Vanes on Blade Surfaces,” SAE Paper 80-0034, 1980.
[27]陳文亮，“小型冷卻風扇之性能與噪音改善研究”，國立台灣科技大學機械工程技術研究所碩士論
文，1998年。
[28]簡嘉宏，“軸流式風扇之設計、模擬與實驗”，國立台灣科技大學機械工程系碩士論文，2010年。
[29]林玟孜，“小型軸流風扇性能之數值與實驗研究”，國立台灣科技大學機械工程系碩士論文，2016
年。
[30]Wu, Y., Jin, Y., and Zhang, L., “Effect of Hub-Ratio on Performance of
Asymmetric Dual-Rotor Small Axial Fan,” Open Journal of Fluid Dynamics, pp.
81-84, March 2013.
[31]嚴文祺，“軸流式風機的性能與噪音特性之整合研究”，國立台灣科技大學機械工程系碩士論文，
2017年。
[32]李虹錤，“小型雙級軸流風扇性能之數值與實驗研究”，國立台灣科技大學機械工程系碩士論文，
2011年。
[33]王福蔭，“利用肋條提升軸流扇性能之數值與實驗研究”，國立台灣科技大學機械工程系博士論
文，2018年。
[34]Lighthill, M. J., “On Sound Generated Aerodynamically. I. General Theory,”
Proc. Roy. Soc. London, Ser. A, Mathematical, Physical and Engineering
Sciences, Vol. 221, No. 1107, pp. 564-587, 1952.
[35]Lowson, M. V., “The Sound Field for Singularities in Motion,” Proc. Roy. Soc.
London, Ser. A, Mathematical, Physical and Engineering Sciences, Vol. 286,
No. 1407, pp. 559-572, 1965.
[36]Arnone, A., “Viscous Analysis of Three-Dimensional Rotor Flow Using a
Multigrid Method,” Journal of Turbomachinery, Vol. 116, No. 3, pp. 435-445,
1994.
[37]Su, M. M., Gu, C. A., and Miao, Y. M., “Numerical Study of Viscous Flow Field
in Mixed-Flow Fan,” Journal of Xi’an Jiaotong University, Vol. 30, No. 10,
pp. 55-63, 1996.
[38]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.
[39]Amano, R. S. and Cheng, X. C., “Aerodynamic Blade Optimal Design of
Turbomachinery,” Proceedings of the International Gas Turbine Congress,
Tokyo, November 2-7, 2003.
[40]Oro, F. J., Diaz, K. A., Morros, C. S., and Tajadura, R. B., ” Unsteady Flow
Analysis of the Stator-Rotor Interaction in an Axial Flow Fan,” Proceedings
of ASME FEDSM’03 4th ASME JSME Joint Fluids Engineering Conference, Honolulu,
Hawaii, USA, July 6-10, 2003.
[41]Kokturk, T., ” Design and Performance Analysis of a Reversible Axial Flow
Fan,” M.S. Thesis, Middle East Technical University, February 2005.
[42]Elhadi, E. E. and Wu, K., “Study of Tip Vortex in Open Axial Flow Fan Using
CFD and PIV Techniques,” 4th International Conference. on Heat Transfer,
Fluid Mechanics and Thermodynamics (HEFAT2005), Egypt, Sept. 2005.
[43]黃家烈、林顯群、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，621-628頁，2000年。
[44]黃家烈，“筆記型電腦散熱風扇之研究”，國立台灣科技大學機械工程技術研究所博士論文，2001
年。
[45]周建安，”小型冷卻風扇在不同流阻下之性能研究”，國立台灣科技大學機械工程技術研究所博士
論文，2004年。
[46]Yang, J. J. and Shan, P., ” Design of a High-Loading Two-Stage Forward Swept
Fan and Investigation on the Swept-Blading Mechanism,” Journal of Aerospace
Power, Vol. 24, Issue 8, pp. 1805-1812, 2009
[47]He, L. and Shan, P.,” Three-Dimensional Aerodynamic Optimization for the Two-
Stage Axial-Flow Fan Based on Work Distribution,” Journal of Aerospace Power,
Vol. 25, Issue 12, pp. 2660-2672, 2010.
[48]ANSI/AMCA Standard 210-16, “Laboratory Method of Testing Fans for Aerodynamic
Performance Rating,” Air Movement and Control Association, Inc., 2016.
[49]CNS 8753, “Determination of Sound Power Level of Noises for Fan, Blower, and
Compressors,” Chinese National Standard, 2016.
[50]https://www.tradeindia.com/fp6078741/Belt-Driven-Propeller-Fan.html
[51]https://www.indiamart.com/proddetail/axial-flow-fan-8063111330.html
[52]Uranga, A., Persson, P., Drela, M., and Peraire, J., “Implicit Large Eddy
Simulation of Transitional Flows over Airfoils and Wings,” 19th AIAA
Computational Fluid Dynamics Conference, San Antonio, Texas, 2009.
[53]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.
[54]Curle, N., “The Influence of Solid Boundaries upon Aerodynamic Sound,”
Proceedings of the Royal Society A: Mathematical, Physical and Engineering
Sciences, Vol. 231, pp. 505–514, 1955.
[55]台達電子，”GFB系列產品風扇資訊”，http//www.delta.com.tw/
product/cp/dcfans/download/pdf/GFB/GFB40x40x56mm.pdf