本文主要目標為建立NACA65系列翼形之資料庫了解翼形增加襟翼結構後之氣動性能，以及增加襟翼之翼形結構應用於軸流風扇時，其流場、壓力場之變化與增加風扇性能的可行性探討。首先將NACA4412翼形實驗數據與數值計算結果比對，其中紊流模型使用LES(大尺度渦漩模擬)計算，而比對後誤差皆在20%之可接受範圍，其中升力與阻力係數的趨勢也相同。接著把翼形改成65系列，作一系列不同雷諾數與攻角之氣動特性分析，並製成資料庫以供風扇設計使用。再來將NACA4412翼型與增加襟翼之結構透過數值計算後，分析兩者之升阻力係數、流場與壓力場，發現其增加襟翼結構之翼形升力比原始翼形增加不少；其中攻角零度時升力增加112%、攻角六度時升力增加46%、攻角為十度時升力增加29%且攻角為十二度時升力增加24%。
在得知翼形增加襟翼結構後升力能大幅度地上升，故將此結構運用於軸流風扇上，因此分別設計採用NACA4412翼形與增加襟翼結構之兩款風扇；結果發現具有襟翼結構之風扇最大流量比原型增加約4%，而在最大壓力則比原型風扇少了3%左右，兩者最大差異是在靜壓為1mm-Aq時，具有襟翼設計之流量比原型風扇減少了38%。仔細分析後發現襟翼風扇葉片下方產生極大的壓力，且越靠近輪殼的區域壓力越大，造成扇葉下方高壓區的氣流往負壓區傳遞，而導致相鄰扇葉吸風面的負壓減少；且在風扇入口處造成流體往外推擠，嚴重地影響葉片吸風面吸引流體進入，且越靠近輪殼的區域此現象越嚴重。從文獻得知翼端間隙對風扇具有嚴重的影響，因此將翼端間隙之參數應用於襟翼風扇上，發現襟翼風扇其性能不因翼端間隙的大小而改變，綜合歸納上述研究成果，清楚地了解襟翼結構在風扇之三維流場的物理現象，及其造成風扇性能降低之機制，這可做為風扇葉片改良設計之參考。

To prevent the overheating and unstable problems, the heat dissipation of electronic products has become a critical and challenging issue due to the demand of dimension reduction. Nowadays, because of its effective heat removing ability and low manufacturing cost, heatsink assembly is the widely-adopted cooling module for handling the thermal- management task. A heatsink assembly is a combination of heatsink and cooling fan; thus the cooling fan plays a vital role and becomes the topic of this thesis. This research focuses on investigating the feasibility of using the flapped airfoil on the small axial-flow fan to enhance its aerodynamic performances, especially the static pressure. The Gurney flap is a small flat plate attached on the trailing edge of airfoil, and it can avoid the unwanted flow from the pressure surface to suction surface for enhancing the lift force substantially.
In this study, the flapped airfoil is utilized in the fan design procedure since the increased lift force on blade may be transferred to the pressure gain, which enables the cooling airflow to overcome the system resistance. Nevertheless, form the simulation results, it is found that some local pressure raises are found on the suction surface of blade, but the total pressure of the discharging air is similar to that of the original fan. To explore the physical mechanism, the comprehensive flow visualization is carried out numerically to identify an unexpected leakage flow, which stems from the pressure surface of one blade to the suction surface of next blade. Evidently, different from the case of single airfoil, this leakage phenomenon is generated by the significant pressure difference caused by the flapped airfoil. It follows that this flow not only diminishes the pressure-raise effect, but also forms an obstacle for the incoming flow near the fan inlet. Consequently, the expected performance enhancement on the axial fan disappears completely. In conclusion, the proposed flapped-airfoil design does not function as expected unless the reversed leakage flow is ceased by proper arrangements based on the flow pattern obtained in this work.

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