苗森春, 罗文, 王晓晖, 杨军虎. 双吸泵作液力透平时叶轮内部能量损失机理分析[J]. 农业工程学报, 2022, 38(22): 12-22. DOI: 10.11975/j.issn.1002-6819.2022.22.002
    引用本文: 苗森春, 罗文, 王晓晖, 杨军虎. 双吸泵作液力透平时叶轮内部能量损失机理分析[J]. 农业工程学报, 2022, 38(22): 12-22. DOI: 10.11975/j.issn.1002-6819.2022.22.002
    Miao Senchun, Luo Wen, Wang Xiaohui, Yang Junhu. Impeller internal energy loss mechanism for a double-suction pump as the turbine[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2022, 38(22): 12-22. DOI: 10.11975/j.issn.1002-6819.2022.22.002
    Citation: Miao Senchun, Luo Wen, Wang Xiaohui, Yang Junhu. Impeller internal energy loss mechanism for a double-suction pump as the turbine[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2022, 38(22): 12-22. DOI: 10.11975/j.issn.1002-6819.2022.22.002

    双吸泵作液力透平时叶轮内部能量损失机理分析

    Impeller internal energy loss mechanism for a double-suction pump as the turbine

    • 摘要: 叶轮是双吸泵作液力透平的核心部件,其性能决定着液力透平的能量回收能力。为研究液力透平叶轮内部能量损失机理,该研究基于熵产理论和数值模拟,采用剪切应力传输(Shear-Stress Transport,SST)湍流模型,分析了不同流量下液力透平各过流部件的能量损失规律。结果表明:叶轮流道内部不稳定流动造成的能量损失和近壁区的内摩擦效应引起的能量损失是整机水力损失产生的主要组成部分;叶轮内部的流动分离、漩涡、动静干涉、强曲率流动以及尾水室内部的死水区对叶轮内部流动状态的反作用等会对能量损失产生较大影响,且平均损失占比高达41%;叶轮近壁区的能量损失主要由叶片和前后盖板与流体间的相互作用导致。研究结果可为双吸液力透平的水力优化设计提供参考。

       

      Abstract: Abstract: An energy recovery device, the double-suction centrifugal pump as the turbine has a wide application prospect in the field of large flow and high-pressure head. The impeller is one of the most important rotating flow components. Its working efficiency can pose a great influence on the energy conversion of the double-suction pump as the turbine. Meanwhile, the internal friction and unstable flow in the impeller can cause the hydraulic loss of the double-suction pump as the turbine, leading to the low efficiency and safety of the pump as the turbine operates. However, the local and wall entropy production rate can be classified as the dissipation caused by irreversible factors, according to the entropy production theory. The local entropy production rate includes the direct entropy production rate caused by non-uniform time average velocity distribution and the turbulent entropy production rate caused by non-uniform fluctuation velocity distribution. Furthermore, the location and size of the irreversible loss in the flow process can be diagnosed by the entropy production theory. In this study, a Shear Stress Transport(SST) κ-ω turbulence model was adopted to clarify the energy loss mechanism in the pump as the turbine impeller. A numerical simulation was then carried out using reasonable mesh division and an accurate boundary layer under Computational Fluid Dynamics(CFD). An external characteristic test was conducted to verify the numerical simulation strategy. Finally, a systematic analysis was made on the energy loss of each flow-through component in the pump under different flow rates, in order to determine the area of high entropy production rate in the pump as the turbine impeller. The energy loss mechanism of the impeller area was clarified to combine with the entropy production theory. The results show that the main reasons for the hydraulic loss in the whole machine were the entropy production rate of turbulent caused by the unstable flow in the impeller channel, and the wall entropy production rate caused by the internal friction in the near-wall area. The average proportions were 41% and 55%, respectively, indicating the extremely low proportion of direct entropy production rate. The total entropy production rate of each flow-through component was ranked in the descending order of the impeller, draft chamber, and volute, where the average proportions were 55%, 30%, and 15%, respectively. In the local entropy production rate of the impeller region, the uneven velocity distribution in the flow field is caused by the flow separation and vortex generated at the suction side and pressure side of the blade, the dynamic and static interference between the volute tongue and the impeller, the bending flow with strong curvature between some impeller flow channels, and the reaction of the backwater zone of the draft chamber on the internal flow state of the impeller, which is the main reason for the increase of the turbulent entropy production rate and energy loss. In addition, the entropy production rate continuously increased on the wall with the increase of flow, due to the dynamic and static interference between the volute tongue and the blade, the interaction between blade, shroud, and fluid, the sharp increase of velocity gradient near the wall, and the increase of shear force and viscous force. At the same time, the flow in the channel posed a great influence on the entropy production of the front cover wall. But, there was no influence on the rear cover wall, which was closely related to the special back-to-back impeller structure of the double suction pump. This finding can provide a strong reference for the hydraulic optimization design of the double-suction pump as the turbine.

       

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