非设计工况下虹吸式出水流道内流数值分析

采用非结构化网格和SIMPLEC算法，对非设计工况下虹吸式出水流道的内部流动进行了数值分析。结果表明，轴流泵后导叶出口断面流速分布不均匀，存在横向流速和剩余环量，与均匀、无旋和轴向出流假定有明显差别。在非设计工况下，虹吸式出水流道内部流态恶化，下降段和出口段的回流区范围增大，驼峰断面和出口断面轴向流速分布均匀度显著下降。在Q=3501／s时，出口断面左右两侧质量加权平均流速分别增大了93．39％和35．54％。研究还发现，流道右侧的流量大于流道左侧的流量，在p=2501／s及Q=4201／s时，左右侧流量比高达1：2．33。非设计工况下流道的水力损失恒大于相同流量时设计工况下的水力损失，左侧的水力损失大于右侧的水力损失，且不符合二次抛物线变化规律。在水泵最高效率点附近，设计工况与设计工况下水力损失的差值有最小值。

Numerical analysis on the internal flow of siphon discharge passages under off-design conditions

Numerical simulation is adopted to analyze the internal flow of a siphon discharge passage under off-design conditions by using unstructured grid and SIMPLEC algorithm.The results show that the velocity profile at the post-vane outlet of an axial-flow pump is unevenly distributed,and there exist transverse velocities and residual circulations,which obviously differ from the hypothesis of uniform,no circulation and axial ouffiow made for the design.The internal flow degenerates under off-design conditions,the backflow regions increase at the descending and outlet segments and the distribution uniformities of axial velocity drop notably at the crest and outlet cross-sections of the passage.When the dischargeis 350l/s,the mass-weighted average velocity at the left and right side increases by 93.39% and 35.54% respectively.The research also reveals that the discharge from the left side of the passage is smaller than that from the right side,the ratio of discharge increases as high as 1:2.33.Compared with the designed flow conditions,the hydraulic loss of the passage under off-design conditions is greater at the same discharge.The head loss of the left side is always greater than that of the right side,and the head loss curves don't comply with the second order parabolic law.A minimum difference of head loss curves between design and off-design conditions appears in the vicinity of the best efficiency point of the pump.