隨著科技進步與雲端產業的蓬勃發展，主要硬體設備伺服器需應付全天候長時間的運作，其穩定性及可靠度更顯得重要，但伺服器本身結構與存放地點機房都是狹小的密閉空間，運作過程過程中所產生的廢熱光靠自然對流散熱是不足夠地；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。有鑑於此，本文將針對廣泛應用於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氣動性能之影響進行討論，先針對入口與出口之風扇分別提出設計方案，而後將兩單級軸流風扇串聯且利用數值模擬分析其流場，藉流場可視化對置於中央之導流葉片參數，與風扇整體流場缺失進行探討與設計改善；而所考量之風扇參數主要有入口葉輪之輪轂外型、出口風扇葉片參數變化、靜葉片之葉片數、入口及出口葉輪之轉速，最後為出口葉輪安裝角對於整體風扇之性能影響，經以上參數分析與改善與討論後，得到一組良好的風扇參數以應用於伺服器內部散熱系統中。
最後為驗證此最適化風扇設計與數值模擬的準確性，將其模型利用CNC加工製造技術實體化，並進行相關氣動力性能與噪音量測；所得之測試結果與數值模擬相互比較後，顯示模擬值與實驗值的性能曲線趨勢相當一致，雖然之間具有一些差異但還在可接受的範圍內，因此證實數值模擬具有一定的準確度。而後將此測試結果與市售風扇相比較後，顯示本文所設計之雙級軸流風扇在維持與市售風扇相當之噪音值下，於氣動性能表現上優於市售風扇，其最大靜壓值高於市售風扇15.7%，而最大流量則是提升1.6%。因此在綜合上述之研究成果顯示，本文所設計之雙級軸流風扇能夠應用於1U伺服器或相關產品內部散熱系統中，其風扇設計流程以及參數討論可提供後續研究一重要的設計參考。

Because of the rapid development of cloud-computing technology, the computing hardware needs to function reliably in a nonstop mode. Also, the demand on reducing computer size, especially the high-performance server, has generated a problem of more heat dissipation being crowded into less space. Moreover, most of the computers are installed inside a small and packed room, which forms a difficult obstacle for heat removing process. Accordingly, the cooling fans not only need to deliver sufficient air flow, but also provide adequate static pressure to overcome the high system resistance. To meet with this challenging request, this work aims to design a two-stage 4056 axial fan (40×40×56 mm3), which is used extensively to generate the high-pressure air stream for the thermal management of 1U server.
First of all, the first-stage and second-stage rotors are designed and verified their performances via the CFD code Fluent separately. Later, with the aids of CFD tool, the detailed flow visualization and the comprehensive parametric study are executed on the complete 4056 fan, which is assembled by combining two rotors together in series. In addition, based on the flow pattern observed, a proper stator is proposed and installed between two impellers to enhance the aerodynamic performance of 4056 fan. The parameters considered here include the hub geometry, the blade shape, the blade angles, the blade numbers, the setting angles, the rotational speeds, and the dimensions of rotors and stator. Subsequently, an adequate parameter setting is obtained after the aforementioned design procedure.
Thereafter, the prototype of optimized design is manufactured by the CNC machine to carry out the corresponding experimental performance verifications. To ensure a reliable outcome, the fan’s performance and noise tests are executed in AMCA and semi-anechoic chambers by following AMCA-210-99 and CNS-8753 codes. By comparing the experimental and numerical results, a remarkable agreement between these performance curves is observed for verifying the reliability of numerical simulation. Besides, under the same rotating speed and similar noise level, the aerodynamic performance of optimum fan is superior to the reference fan by 1.6% and 15.7% increases on its maximum flow rate and maximum static pressure, respectively. In summary, this study successfully establishes a reliable and systematic scheme to design the two-stage axial fan for the cooling management of 1U server or the related products. Besides, the corresponding performance influences caused by important fan parameters are analyzed and summed up for serving as the design reference for the two-stage axial fan.

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