本研究目標為家用雙級同軸離心式泵浦之性能改善，其特點為採用兩級葉輪固定在同軸，故只需要一個馬達並可減少安裝所需空間，但這也使兩級動葉輪間的流道變得十分複雜，離開第一級葉輪的流體必須在極狹窄空間轉180度，再由外圍以徑向往中心進入第二級葉輪入口 ; 另外離開第二級動葉輪的流體也有著相似的情形，必須在短距離轉向才能由泵出口排出，上述問題成為提升泵浦性能及效率時的巨大挑戰。本研究選用CFD軟體Fluent作為分析工具，對同軸離心泵浦做流場聲場的數值模擬，由流場可視化了解內部流場，進一步提出相對應之改善方案，主要的改善對象分為葉輪及流道 ; 首先對靜葉輪和動葉輪進行參數優化，其中靜葉輪考量的參數有入口角度、葉片擺設方向及葉數，而動葉輪包括葉片角度和葉片數。
數值參數分析結果顯示，動葉輪在第一級11葉、第二級8葉、入口角60∘和出口角50∘的參數組合下，其流量在低揚程(5.56m)時增加7.9% (由138到148.9 LPM)，於高揚程(24m)時上升67% (由34.8到58.1 LPM) ; 至於效率部份，則在低揚程維持在18.1%，另外高揚程則有顯著提升從45.0%提升到52.9%。接著進行各連接流道部份之改良，包括進口與出口銜接流道的流線化，結果顯示成功地去除流場混亂與局部高壓區，也提升高揚程之流量和效率。最後搭配優化葉輪和改良流道的新泵浦設計，其數值計算結果顯示，於24m的高揚程操作情形下，其流量可增加到72.8 LPM，為原始設計的2倍多，靜壓效率也再增加4%到56.9%，同時所產生的聲壓分貝值則維持不變。綜合歸納而言，本數值研究成功建立一套系統分析模式，可用來改良泵浦的靜葉輪、動葉輪及流道，且此方法對於雙級同軸離心式泵浦在高揚程時有明顯的效果。

This research intends to enhance the aerodynamic performance of a two-stage coaxial centrifugal pump, which is used extensively for the household water supply. Noticeably, the coaxial arrangement on two impellers, which needs only one motor, is adopted to reduce the installation space and the pump cost. However, it also induces a tremendous difficulty in designing a proper flow pathway between two parallel impellers fixed on the same axis. Clearly, the outflow of the 1st rotor needs to reverse its direction completely at the outer periphery within a tiny distance between the rotor and the circular housing; thereafter, this stream must flow radially inward to reach the 2nd rotor inlet uniformly for ensuring effectively energy transfer along the blade passage. Moreover, the similar challenge exists for the outflux at the 2nd rotor making two vertical turns before reaching the pump discharge. The foregoing problems form an incredible task for engineers to secure a good aerodynamic performance with a fair efficiency, and also becomes the motivation of this work.
With the aids of CFD technology, this study chooses Ansys Fluent as the analysis tool to examine flow field, aerodynamic performance, and static efficiency of the reference pump. Thereafter, the adverse flow phenomena are identified for proposing further improvements. This numerical study consists of two improving efforts on rotors and flow paths in sequence. Firstly, the comprehensive parametric studies on the stator and rotor is executed systematically to attain an optimum rotor set. The parameters considered here include the rotating direction and the inlet blade angle of stator, the blade angles and numbers of the running impellers. Consequently, with 11 and 8 blades for the 1st and the 2nd running rotors, the combination of 60∘inlet and 50∘outlet blade angles results in the flowrate increases of 7.9% (from 138.0 to 148.9 LPM) and 67% (from 34.8 to 58.1 LPM) for the low-head (5.56 m) and the high-head (24 m) operating points, respectively. Besides, the static efficiencies are near the same at 18.1% for the 5.6-m head, and enhanced significantly from 45.0% to 52.9% for the 24-m operating point.
Lastly, operating under the 24-m head, this new pump with the optimized rotor and the improved flow pathway yields a remarkable flowrate enlargement up to 72.8 LPM (i.e., twice of the original output) and an extra 4% efficiency rise with the same sound pressure level generation. In summary, this numerical investigation successfully establishes a systematic scheme to analyze the performance influences induced by various parameters on the stator, the rotor, and the connecting passageway. Furthermore, the results of aforementioned parametric studies are applied to optimize this 2-stage, coaxial centrifugal pump for attaining the significant enlargements on flowrate and efficiency for the high-head operating condition.

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