機翼之翼尖小翼設計具有增加升力與節省燃料的功能，本研究擬將之應用於軸流扇設計中，以達到減緩翼尖渦流進而提升風機性能的效用，首先選定波音737的融合式小翼應用於6038軸流扇，並以數值工具對增設小翼所產生之氣動力性能與流場差異進行比較。透過CFD商用軟體對機翼在有與無融合式小翼下，就其於不同攻角之升、阻力進行分析，結果顯示具小翼機翼之升力大幅提高，在攻角到達失速區以前，具小翼機翼的升力都較裸翼高48~57%；由於軸流扇運轉之操作雷諾數較飛機低，在此藉由建立小翼於低操作雷諾數的升、阻力資料，來確認小翼應用於軸流扇也有類似效果。接著選用市售6038軸流扇作為基準風扇，經模擬流場發現其翼端間隙之回流非常嚴重，故將融合式小翼應用在基準風扇中，以完成具小翼風扇之設計來改善此問題；在模擬比對兩者之氣動力性能後，發現具小翼風扇之回流現象減緩、且最大流量上升3.4%(65.6 CFM增為67.9 CFM)，而最大靜壓則因總體葉片面積略減，而由77.4 mmAq略降為71.2 mmAq。尤其值得注意是，在中低阻抗操作點(30%最大靜壓)產生最大65.8%之流量升幅，而扭矩在低阻抗操作點(15%最大靜壓)有24.8%最大提升，皆可證明其升力在此阻抗區間有所提高。至於中阻抗操作點 (50%最大靜壓)至最大靜壓點的操作區間，具小翼風扇之扭矩與軸向受力皆較低，代表在高阻抗操作區間具小翼風扇擁有較好的效率。
確認融合式翼尖小翼對軸流扇之氣動性能有幫助後，本文系統性地改動小翼設計參數、移除部分小翼、及更動小翼方向，以期找出各參數之影響及優化方向；模擬分析結果彙整顯示，最對稱之具小翼風扇-TT型的表現最佳，可以在最大壓力不變下提高3.7%之最大流量，且中低阻抗操作點(30%最大靜壓)之流量也上升4.4%。移除部分小翼之規劃皆不利於性能，其中以移除1/2小翼型之最大壓力、流量及中低阻抗操作點之流量降低最多，分別為7.0%、11.8%以及49.3%；而朝葉片吸、壓力面各生長小翼之方案，能更有效地減弱翼尖渦流且增加葉片面積，使風機之流量與壓力都提高，而向壓力面生長小翼之提升效果則受其軸向面積影響甚大，若不足則無法彰顯減弱翼尖渦流之效用。綜合歸納上述結果，當融合式翼尖小翼應用於轉速較低之軸流扇，確實能達到減緩翼尖渦流的效用，進而提高升力與強化風機之性能。

This research intends to investigate whether the aerodynamic performance of a small axial-flow fan can be enhanced by introducing the winglet, which is extensively used in the aircraft wing for increasing lift and saving fuel. Here, the blended winglet design of Boeing 737 is chosen as the base geometry to be applied on the rotor blade of a 6038 (60x60x38 mm3) axial-flow fan. Firstly, within the framework of CFD technology, performance superiority of the airplane wing with a winglet is confirmed under a range of low Reynolds numbers corresponding to the fan operation. The numerical flow field reveals that the strength of wingtip vortices are diminished significantly after adding the wingtip. Also, the lift of wing is 48~ 57% higher than that of the wing without wingtip under various attack angles before reaching the stall zone. Thereafter, the original 6038 fan is analyzed numerically to obtain its aerodynamic performance and flow field for serving as the comparison basis. And, serious reverse flow is identified in the tip region of this reference fan. Obviously, this flow feature is appropriate for utilizing the winglet design to reduce the wingtip vortex by preventing the pressure leakage generated from the pressure surface to the suction surface of rotor blade. Later, a blended winglet pointing to the pressure surface near the rotor wingtip is implemented on the reference fan for performance improvement. After comparing the calculated performances of two fans with/without the winglet, it is found that winglet addition causes a 3.4% (65.6 to 67.9 CFM) increase and an 8.0% drop (77.4 to 71.2 mmAq) on the maximum flow rate and static pressure, respectively. Note that, the largest increase (65.8%) on volume flow rate is found at the operating point of 30% Pmax. Also, the required torque and axial force applied on the rotor reach the maximum increases of 24.8% and 59.2% at the low-impedance operating point (15% of Pmax). Thus, the lift is substantially enhanced at this operating point. Regarding the middle-to-high resistance range (50~100% of Pmax), smaller axial force and torque on the rotor are observed and can result in a higher fan efficiency.
Subsequently, the parametric study on the winglet design is executed systematically with the aids of numerical simulation to attain the proper design approach. The design parameters considered here include twisting the winglet, adding the upper/downward winglet, and deleting partial winglet. The outcome shows the best winglet, which is featured with a nearly symmetric geometry and denoted as TT model, can produce an extra 3.73 and 4.44% on the flow rates under the free-delivery and the mid-low impedance (30% Pmax) operating point, while the maximum static pressure remains the same. Also, the removal of partial winglet demonstrates negative effects on the fans performance. Regarding the addition of upper/downward winglets, CFD simulation indicates that the downward winglet can retain the high-pressure on the pressure surface from leaking to the free surface, thus can diminish the winglet vortex, while the upper winglet cannot function properly to prevent this vortex generation. Also, adding both downward and upper winglets is capable to lessen the wingtip vortex and increase the blade surface; thus, the maximum flow rate and static pressure are both enlarged. Nevertheless, the complex geometry of this design results in the technical and economic obstacles for its mass production. In addition, the performance enhancement induced by the downward winglet (toward the pressure surface) is severely affected by the tip area of winglets, which should be large enough to weaken the wingtip vortices. In conclusion, this study successfully demonstrates that adding the blended winglet on rotor blade can decrease wingtip vortices, increase the lift, and enhance the performance of an axial-flow fan.

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