|
|
|
| Analysis on characteristics of tip cavitation in an axial-flow pump based on PANS model |
| SHI Lei, ZHANG Desheng, CHEN Jian, GENG Linlin, LIU Junlong |
| National Research Center of Pumps, Jiangsu University, Zhenjiang, Jiangsu 212013, China |
|
|
|
|
Abstract Tip cavitation in a scaled axial-flow pump is simulated by using a partially-averaged Navier-Stokes(PANS)model and Zwart cavitation model at a rated flow rate and under a specific NPSH. The numerical results are compared with the experimental data made by making use of high-speed photography. Different types of tip vortex cavitation and leakage vortices are exploited, and the locations where cavitation in tip leakage vortex core is mostly prone to occur are identified; the cavitating flow fields at various dimensionless chord lengths are analyzed as well. The simulated pump cavitation performance curve agrees so well with the experimental data that the largest error is 5.8% only. The tip leakage vortex core has the maximum vortex intensity coefficient and minimum pressure coefficient at a dimensionless chord length of λ=0.30~0.35, indicating a location where cavitation is mostly pronounced to emerge based on vorticity method. Based on the method, the vortex center is defined as a point with the maximum vortex intensity. Due to the lowest pressure in the vortex core, the formation and development of cavitation in the tip region usually couples with the evolution of vortex structure. When migrating towards the pressure side of the neighboring blade, the tip leakage vortex will interact with the casing wall, resulting in counter-rotating vortex near the end-wall. At the trailing edge of blade tip, separated and induced vortices are generated, enhancing the instability of flow field between the impeller passages. As moving towards the neighboring blade pressure surface, the separation vortex can cause a change in blade loading distribution. As a consequence of increased leakage flux, the cavitation in the blade tip becomes more extensive, resulting in a severe degradation in the pump performance.
|
|
Received: 28 August 2015
|
|
|
|
| [1]张德胜, 陈健, 张光建, 等. 轴流泵叶顶泄漏涡空化的数值模拟与可视化实验研究[J]. 工程力学, 2014, 31(9): 225-231. ZHANG Desheng, CHEN Jian, ZHANG Guangjian, et al. Numerical simulation and visualization study on tip leakage vortex cavitation in an axial-flow pump[J]. Engineering mechanics, 2014,31(9): 225-231.(in Chinese)[2]MAILACH R, LEHMANN I, VOGELER K. Rotating instabilities in an axial compressor originating from the fluctuating blade tip vortex[J]. Journal of turbomachinery, 2000,123(3): 453-460.[3]HAH C. Investigation of turbulent tip leakage vortex in an axial water jet pump with large eddy simulation[C]//Peoceedings of ASME 2012 Fluids Engineering Division Summer Meeting collocated with the ASME 2012 Heat Transfer Summer Conference and the ASME 2012 10th International Conference on Nanochannels, Microchannels, and Minichannels, 2012: 135-142.[4]SORANNA F, CHOW Y C, UZOL O, et al. Flow structure and turbulence in the tip region of a turbomachine rotor blade[C]//Proceedings of the ASME Turbo Expo 2007: Power for Land, Sea and Air, 2007: 1687-1699.[5]TABAR M T S, POURSHARIFI Z. An experimental study of tip vortex cavitation inception in an axial flow pump[J]. World academy of science, engineering and technology, 2011, 5(1):86-89.[6]TAN D, LI Yuanchao, WILKES I, et al. Visualization and time resolved PIV measurements of the flow in the tip region of a subsonic compressor rotor[C]//Proceedings of ASME Turbo Expo 2014: Turbine Technical Conference and Exposition, 2014: V02AT37A051-V02AT37A051.[7]WU Huixuan, MIORINI R L, KATZ J. Analysis of turbulence in the tip region of a waterjet pump rotor[C]//Proceedings of ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting collocated with 8th International Conference on Nanochannels, Microchannels, and Minichannels, 2010: 699-711.[8]黎耀军, 沈金峰, 严海军, 等. 叶顶间隙对轴流泵轮缘泄漏流动影响的大涡模拟[J]. 水利学报, 2014, 45(2): 235-242. LI Yaojun, SHEN Jinfeng, YAN Haijun, et al. Investigation of the effects of tip-gap size on the tip-leakage flow in an axial-flow pump using LES[J]. Journal of hydraulic engineering, 2014,45(2): 235-242.(in Chinese)[9]黎耀军, 沈金峰, 洪益平, 等. 轮缘间隙对轴流泵内部非定常流场的影响[J]. 排灌机械工程学报, 2013,31(8): 667-673. LI Yaojun, SHEN Jinfeng, HONG Yiping, et al. Effect of tip clearance on unsteady flow in axial-flow pump[J]. Journal of drainage and irrigation machinery engineering, 2013,31(8): 667-673.(in Chinese)[10]施卫东, 邵佩佩, 张德胜, 等. 轴流泵运行工况和叶顶间隙对叶顶泄漏涡轨迹的影响[J]. 排灌机械工程学报, 2014,32(5): 373-377. SHI Weidong, SHAO Peipei, ZHANG Desheng, et al. Influence of operational condition and tip clearance size on trajectory of tip leakage vortex[J]. Journal of drainage and irrigation machinery engineering, 2014,32(5): 373-377.(in Chinese)[11]张德胜, 王海宇, 施卫东, 等. 不同空化数下轴流泵叶顶间隙区空化特性[J]. 农业机械学报, 2014,45(2): 115-121. ZHANG Desheng, WANG Haiyu, SHI Weidong, et al. Tip clearance cavitation characteristics in axial flow pump under different cavitation numbers[J]. Transactions of the CSAM, 2014, 45(2): 115-121.(in Chinese)[12]DREYER M, DECAIX J, MÜNCH-ALLIGNÉ C, et al. Mind the gap: a new insight into the tip leakage vortex using stereo-PIV[J]. Experiments in fluids, 2014,55(11): 1-13.[13]DECAIX J, BALARAC G, DREYER M, et al. RANS and LES computations of the tip-leakage vortex for different gap widths[J]. Journal of turbulence, 2015,16(4): 309-341.[14]YOU D, WANG M, MOIN P, et al. Effects of tip-gap size on the tip-leakage flow in a turbomachinery cascade[J]. Physics of fluids, 2006,18(10): 105102-1-105102-14.[15]GIRIMAJI S S. Partially-averaged Navier-Stokes model for turbulence: a Reynolds-averaged Navier-Stokes to direct numerical simulation bridging method[J]. Journal of applied mechanics, 2006,73(3): 413-421.[16]黄彪, 王国玉, 权晓波, 等. PANS 模型在空化湍流数值计算中的应用[J]. 应用力学学报, 2011,28(4): 339-343. HUANG Biao, WANG Guoyu, QUAN Xiaobo, et al. Application of the partially-averaged Navier-Stokes method in computations of turbulent cavitating flows[J]. Chinese journal of applied mechanics, 2011,28(4): 339-343.(in Chinese)[17]施卫东, 张光建, 张德胜, 等. 基于 PANS 模型的水翼非定常空化特性研究[J]. 华中科技大学学报(自然科学版), 2014,42(4): 1-5,10. SHI Weidong, ZHANG Guangjian, ZHANG Desheng, et al. Investigation of unsteady cavitation around hydrofoil based on PANS model[J]. Journal of Huazhong University of Science and Technology(natural science edition), 2014,42(4):1-5,10.(in Chinese)[18]ZHANG Desheng, SHI Weidong,(BART)van ESCH B P M, et al. Numerical and experimental investigation of tip leakage vortex trajectory and dynamics in an axial flow pump[J]. Computers & fluids, 2015,112: 61-71.[19]WU Huixuan, MIORINI R L, KATZ J. Measurements of the tip leakage vortex structures and turbulence in the meridional plane of an axial water-jet pump[J]. Experiments in fluids, 2011,50(4): 989-1003. |
|
|
|
