泵(Pump)的設計通常是以直管入流條件為主，但實際工程中安裝空間限制、結構設計等原因，造成入口流動不均勻，導致泵效率降低，彎管入流是影響因素之一。本研究使用CAD軟體建立離心泵之幾何模型，以數值模擬方法，分析不同彎管入流、磨損環間隙、表面粗糙度等對離心式泵的性能影響。數值模擬之控制方程式為三維雷諾平均Navier-Stoke方程，壓力項與速度項之耦合計算使用Couple法則，紊流模式為三方程k-ω SST模型，流場則假設為不可壓縮流體。經由紊流模式選用、網格獨立性分析，模擬結果和實際實驗值相吻合；在四個彎管入流條件中，45度一倍葉輪直徑長彎管，是所有彎管效率和揚程最好的，效率提升主要在於彎管角度的減少；模擬0.15mm、0.2mm、0.5mm三種不同磨損環間隙，經由揚程和效率曲線可以看出，磨損環間隙大小對泵效率有明顯影響，且0.15mm總體效率略大於0.2mm，但考量到那些微的提升效益和實際製程的技術成本問題，選擇0.2mm間隙成本效益為最高；經由0.1、0.05、0.01mm表面粗糙度比較，過了額定流量後，當流量越大，泵效能損耗越劇烈，結果顯示數值模擬的揚程會高於實驗量測，考量粗糙度效應數值模擬值則會接近實驗值；模擬粗糙度在0.1mm時，揚程效率曲線和實驗最相符。

The pump performance design is usually evaluated with inflow conditions on the straight pipe under various volumetric flow rates. However, in the actual operational environment, due to installation space limitations, structural enforcement, and other special reasons the pump performance is decayed more than the engineer expected value. The blend pipe cause uneven inlet flow resulting in a degree of reduced pump efficiency that is unknown for the pump industry. The effects of inflow blend pipes, wall roughness, and seal clearness on the output stoke of centrifugal pump under various flow rates are investigated in this works by CFD method.
In this study, the first step is using CAD software of SolidWorks2014 to establish the geometric model of the centrifugal pump provided by the manufacturer. Based on the original design, some modifications to the model are made about the connected elbow inflow pipes and seal clearance. The second step is to employ the CFD tools to finish the computational grids. The performance of the centrifugal pump was analyzed by the numerical simulation software based on to control volume method. The conservation equations of the numerical simulation are the steady, incompressible three-dimensional Reynolds-averaged Navier-Stoke equations. The coupling calculation of the pressure term and the velocity term use the Couple law, the turbulence model is a two-equation SST k-ω model. The working fluid is pure water and the flow field is assumed to be an incompressible fluid flow.
After finished the selection of turbulent flow mode and grid independence analysis, the numerical methods are specified and the simulation results are compared with the actual experimental values. The performance cures are well agreement with each other. Among the four inflow conditions (a combination of 450 and 900 elbow with 0.5 and 1 times diameter of straight pipes), the 450 elbows with one time of diameter long pipe have the best efficiency. The worst case belongs to the model of 900 elbow with short straight pipe due to the uneven impingement flow on the propeller blades.
Simulation runs are conducted for three different wear ring gaps of 0.15mm, 0.2mm, and 0.5mm under various flow rates. From the stoke and efficiency with respect to the flow rate curves, it can be seen that the value of the wear ring gap has a significant impact on the output efficiency of the pump, and the overall efficiency of 0.15mm is slightly greater than 0.2mm. The reduction in the seal clearance shows a positive effect on the improvement of the pump’s performance. However, due to complex factors in the manufacturing process, it is suggested that a model with 0.2mm seal clearance is more suitable for the present pump company. Inspections on the results of cases with the surface roughness of 0.1, 0.05, and 0.01mm show that the performance is obviously dropped when the tested flow rates are higher than the on-design point. Generally, the increase in the wall roughness resulted in the reduction of pump efficiency.
When the flow rate is fixed, it is showing that the head of the numerical simulation of smooth wall boundary conditions will be higher than those of experimental measurements. After correcting the numerical with the actual wall roughness of the pump body, the predictions are more fitted to of experimental from test platforms. It means that the wall roughness effect should be considered in the CFD simulations of centrifugal pumps.

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