Abstract：During the operation of Venturi injector, when the negative pressure in throat portion gets lower, the suction flow rate will increase. But a lower negative pressure will cause cavitation easily, which may damage the surface of internal structures and finally affect the suction flow rate and the fertigation uniformity of micro-irrigation system. The internal flow of a Venturi injector with 1.5 inch dia-meter for both inlet and outlet was observed using high-speed photography technique. The relations between the cavitation characteristics, the inlet pressure, and pressure differences between inlet and outlet were analyzed. The impact of cavitation on the injection performance was also investigated. The results indicate that the cavitation occurred firstly in the junction of constriction and throat portions. With the increase of the pressure difference, cavitation gradually aggravated and the bubbles extended from the throat to the diffusion portion, meanwhile the growth rate of the suction flow rate decreased gradually. When the pressure difference increased to a certain value, the critical cavitation occurred, while the suction flow increased no longer. The increase of suction flow rate would impact on the working fluid, causing the bubbles to move toward the upper side of the diffusion portion and distributed unevenly. The reflux phenomenon occurred obviously in the rear of the diffusion portion leading the bubbles shed periodically.
[1]严海军,陈燕,徐云成,等. 文丘里施肥器的空化特性试验研究[J]. 排灌机械工程学报, 2013, 31(8): 724-728. Yan Haijun,Chen Yan,Xu Yuncheng, et al. Experimental investigation on cavitation characteristics of Venturi injector[J]. Journal of Drainage and Irrigation Machinery Engineering, 2013, 31(8): 724-728.(in Chinese)[2]Ghassemi H, Fasih H F. Application of small size cavitating venturi as flow controller and flow meter[J]. Flow Measurement and Instrumentation, 2011, 22(5): 406-412.[3]Stutz B, Reboud J L. Experiments on unsteady cavita-tion[J]. Fluids, 1997, 22(3): 191-198.[4]Stutz B, Reboud J L. Two-phase flow structure of sheet cavitation[J]. Physics of Fluids, 1997, 9(12): 3678-3686.[5]Barre S, Rolland J, Boitel G, et al. Experiments and modeling of cavitating flows in venturi: Attached sheet cavitation[J]. Fluids, 2009, 28(3): 444-464.[6]Yazici B, Tuncer I H, Ali Ak M. Numerical & experimental investigation of flow through a cavitating venturi[C]//Recent Advances in Space Technologies, 2007: 236-241.[7]Coutier-Delgosha O, Vabre A, Hocevar M, et al. Local measurements in cavitating flow by ultra-fast X-Ray imaging[C]//Proceedings of the ASME Fluids Engineering Division Summer Conference,2009:371-379.[8]Sato K, Hachine K, Saito Y. Inception and dynamics of traveling-bubble-type cavitation in a venturi[C]//4th ASME/JSME Joint Fluids Eng Conf,2003: 279-285.[9]Sayyaadi H. Instability of the cavitating flow in a venturi reactor[J]. Fluid Dynamics Research, 2010, 42(5): 055503.[10]龙新平, 王磊. 液体射流泵空化噪声与振动试验[J]. 排灌机械, 2007, 25(4): 1-5. Long Xinping, Wang Lei. Experiment on cavitation noise and vibration in liquid jet pump[J].Drainage and Irrigation Machinery, 2007, 25(4): 1-5.(in Chinese)[11]龙新平, 程茜, 韩宁,等. 射流泵空化流动的数值模拟[J]. 排灌机械工程学报, 2010, 28(1): 7-11. Long Xinping, Cheng Qian, Han Ning, et al. Numerical simulation on cavitating flow within jet pump[J]. Journal of Drainage and Irrigation Machinery Engineering, 2010, 28(1): 7-11.(in Chinese)[12]杨雪龙,龙新平,肖龙洲,等. 不同湍流模型对射流泵内部流场模拟的影响[J]. 排灌机械工程学报, 2013, 31(2): 98-102. Yang Xuelong,Long Xinping,Xiao Longzhou,et al. Influence of different turbulence models on simulation of internal flow field of jet pump[J]. Journal of Drainage and Irrigation Machinery Engineering, 2013, 31(2): 98-102.(in Chinese)[13]孙艳琦, 牛文全. 文丘里管结构参数对其水力性能的影响[J]. 西北农林科技大学学报:自然科学版, 2010, 38(2): 211-218. Sun Yanqi, Niu Wenquan. Effects of Venturi structural parameters on the hydraulic performance[J]. Journal of Northwest A&F University:Natural Science Edition, 2010, 38(2):211-218.(in Chinese)[14]Brennen C E. Hydrodynamics of Pumps[M]. Cambridge:Cambridge University Press, 2011.[15]杨庆, 张建民, 戴光清, 等. 脉动压力对空化的影响[J]. 四川大学学报:工程科学版, 2004(4):19-21. Yang Qing, Zhang Jianmin, Dai Guangqing, et al. Effects of fluctuation pressure on cavitation[J]. Journal of Sichuan University:Engineering Science Edition, 2004(4):19-21.(in Chinese)[16]An H, Plesniak M W. Cavitation structures in a venturi flow with various backward facing steps[J]. Journal of Fluids Engineering, 2008, 130(7): 713041-713047.
