Abstract:The threedimensional unsteady flow field in a mixedflow pump was calculated by means of the large eddy simulation (LES), subgrid scale model and sliding mesh technique in order to analyze the instability in head curve and flow characteristics caused from the interaction between impeller and guide vane in the pump under low flow rate conditions. The experimental results showed the headcapacity curve exhibits a positive slope at 60%Qd and 85%Qd operating conditions, and the error between predicted and experimental results is less than 4%, suggesting LES can predict the positive slope characteristic accurately. On this basis, the flow mechanism for the unstable characteristic was analyzed. The simulated results showed that the fluid tangential velocity is distributed nonaxisymmetrically in the impeller inlet evidently. Because of the stall of flow in the impeller and guide vane passages, there is a large scale vortex structure on the blade surface and the hub surface at the leading ledge of guide vane. The scale of the vortices in the guide vane passages is larger than that in the impeller. It is apparent that the pressure fluctuates periodically along the axial direction, allowing the vortex zone extends into the middle of guide vane passage from the suction side of guide vane. The core of large scale vortex is attached to the suction side at the middle span of the guide vane where pressure fluctuation is minimal; moreover, the rotational direction of the core is the same as the impeller.
[1]王福军,张玲,张志民.轴流泵不稳定流场的压力脉动特性研究[J].水利学报, 2007,38(8):1003-1009.Wang Fujun, Zhang Ling, Zhang Zhimin. Analysis on pressure fluctuation of unsteady flow in axialflow pump[J].Journal of Hydraulic Engineering, 2007,38 (8):1003-1009.(in Chinese)[2]Kato C, Mukai H, Manabe A. Largeeddy simulation of unsteady flow in a mixedflow pump[J]. International Journal of Rotating Machinery, 2003,9(1):345-351.[3]施卫东,邹萍萍,张德胜,等.高比转速斜流泵内部非定常压力脉动特性[J].农业工程学报,2011,27(4): 147-152.Shi Weidong, Zou Pingping, Zhang Desheng,et al.Unsteady flow pressure fluctuation of highspecificspeed mixedflow pump[J].Transactions of the CSAE,2011,27(4):147-152. (in Chinese)[4]施卫东,冷洪飞,张德胜,等.轴流泵内部流场压力脉动性能预测与试验[J].农业机械学报,2011,42(5): 44-48.Shi Weidong, Leng Hongfei, Zhang Desheng, et al. Performance prediction and experiment for pressure fluctuation of interior flow in axial flow pump[J].Transactions of the Chinese Society for Agricultural Machinery, 2011, 42(5): 44-48. (in Chinese)[5]王福军,张玲,黎耀军,等.轴流式水泵非定常湍流数值模拟的若干关键问题[J].机械工程学报,2008,44 (8):73-77.Wang Fujun, Zhang Ling, Li Yaojun, et al. Some key issues of unsteady turbulent numerical simulation in axialflow pump[J].Chinese Journal of Mechanical Engineering, 2008,44 (8):73-77.(in Chinese)[6]常书平,王永生,魏应三,等.喷水推进器内非定常压力脉动特性[J]. 江苏大学学报:自然科学版, 2012, 33(5): 522-527.Chang Shuping, Wang Yongsheng,Wei Yingsan, et al. Pressure fluctuation of unsteady flow in waterjet[J]. Journal of Jiangsu University:Natural Science Edition, 2012,33(5):522-527.(in Chinese)[7]潘中永,吴涛涛,潘希伟,等.斜流式泵喷水推进器内部流动不稳定性分析[J].华中科技大学学报:自然科学版,2012,40(9):118-121.Pan Zhongyong, Wu Taotao, Pan Xiwei, et al. Instability analysis of internal flow in mixedflow pump waterjet propulsion [J]. Journal of Huazhong University of Science and Technology:Natural Science Edition, 2012,40 (9):118-121. (in Chinese)[8]潘中永,李俊杰,李晓俊,等.斜流泵不稳定特性及旋转失速研究[J].农业机械学报,2012,43(5):64-68.Pan Zhongyong, Li Junjie, Li Xiaojun, et al. Performance curve instability and rotating stall[J].Transactions of the Chinese Society for Agricultural Machinery, 2012,43 (5):64-68.(in Chinese)[9]Miyabe M, Maeda H, Umeki I, et al. Unstable headflow characteristic generation mechanism of a low specific speed mixed flow pump [J]. Journal of Thermal Science,2006,15(2): 115-120,144.[10]邴浩,曹树良,谭磊,等.速度矩分布规律的参数化描述及对混流泵性能的影响[J].农业工程学报,2012,28(13):100-105.Bing Hao, Cao Shuliang, Tan Lei, et a1.Parameterization of velocity moment distribution and its efects on performance of mixedflow pump[J].Transactions of the CSAE,2012,28(13):100-105.(in Chinese)[11]Smagorinsky J. General circulation experiments with the primitive equations—I: The basic experiment[J]. Monthly Weather Review, 1963,91 (3):99-164.[12]Slack M D, Prasad R O, Bakker A, et al. Advances in cyclone modeling using unstructured grids[J].Chemical Engineering Research and Design,2000,78 (A):1098-1104.