隨著電腦主機朝微型化發展，狹小的散熱空間使得系統阻抗上升，進而影響散熱效果，因此提升散熱風扇之性能即成為研究重點，本文以常見的十四公分軸流風扇作為研究目標。首先建立一套具有可信度的翼型升、阻力之分析模擬方法，接著挑選扇葉所需據有高失速角的四種翼型，進行低雷諾數之氣動力資料庫建立，提供風扇葉片外型有合適且可靠的翼型選擇；此外，本研究也嘗試於葉片尾緣加入打孔的結構，並探討此結構對風扇流場及性能的影響。模擬研究結果顯示，使用在低雷諾數及高攻角條件下據有高升力係數之翼型的風扇葉片，可使軸流風扇在最大壓力點有較明顯的變化，但在最大流量點並無明顯提升；其中以E216翼型風扇的效果最佳，其最大靜壓可提升11.2%。而在葉片尾緣鑽孔的結構，藉由調整孔洞角度、直徑及位置等參數後，在r=21mm及r=35mm位置都加入傾角110°的兩個直徑1.0mm孔，於最大流量有2.4%的提升，但最大壓力則影響不大，此外，輪毂附近的回流得到顯著改善，在最大流量點和最大壓力點的能源效率因子分別提高了3.5%和9%。綜合以上研究成果顯示，適當的翼型挑選及孔洞結構能提供正向的影響，而本研究之完成可作為各型軸流風扇提升性能的設計參考。

Due to the increasing compact-size demand, the system resistance of PC product is strengthening and turning into a critical thermal-design task. Thus, performance enhancement of the axial-flow cooling fan has attracted significant attention and become the goal of this thesis. Firstly, an extensively-used axial-flow fan with 140mm diameter and 25mm thickness (denoted as 14025) is chosen as the research target. Later, its flow pattern and aerodynamic performance are analyzed and calculated with the aids of CFD codes Fluent. Subsequent, a low-Reynolds-number airfoil database is established for the utilization on small cooling fan to replace the inappropriate NACA airfoil databank, which is prepared for the high speed applications. Several high-stall-angle blade geometries, including E216, GOE430, NACA4412, and SG6043, are selected to construct a reliable database via CFD calculations incorporated with a dependable turbulent model. Additionally, holes are imposed near the trailing edge of impeller blade to form a channel, which can induce a high-pressure airstream from the lower pressure surface to the upper suction surface for diminishing the negative effect of separation phenomenon. Subsequently, a systematic parameter analysis on the drilling holes is executed to obtain the best hole design. In this work, the design parameters considered include the hole diameter, the inclined angle, the radius location near the hub, and the distance from the blade trailing edge.
As a result. there is no significant enhancement on the maximum flow rate when the high-stall-angle airfoils are applied on the fan design. However, an obvious increase 11.2% on the maximum pressure is observed for an impeller with E216 blades. Regarding drilling hole on the rotor blade, the best 2.4% increase of flow rate is found when two 1mm-diameter holes with an 110° inclined angle are added on each E126-airfoil blade at 3mm away from the trailing edge in both r=21mm and r=35mm locations. Moreover, the reversed flow near the hub is improved considerably to yield a better energy efficiency factor by 3.5% and 9% increases at the free-delivery and non-delivery points, respectively. In conclusion, this study successfully constructs a reliable airfoil database for the low-Reynolds-number fan design to improve its performance. Also, adding holes on the blade does result in a superior flow field, higher flowrate, and better energy efficiency.

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