低扬程泵站弯肘形出水流道内Dean涡的演变及流动控制研究

Hydraulic loss in elbow outlet conduit is the key problem that needs to be solved to improve the efficiency of low-head pump stations, which requires a deep understanding into the mechanism of secondary flow loss and innovative methods for control this flow that is intrinsically unsteady and 3D. In this study, the Dean vortex theory is firstly used to investigate the flow in elbow outlet conduit. A combined numerical (CFD) and experimental (PIV) approach is utilized to systematically examine the influence of varying inlet flow condition, curvature and cross-sectional shape of the conduit on the generation/evolution of the secondary Dean vortices along the conduit. Based on the variation of the hydraulic loss of outlet conduit obtained by performance test and the flow instability detected by a newly-proposed method named ‘vortex core criterion’, the relationship between the flow instability characteristics and hydraulic loss caused by inlet disturbance is established theoretically. The advantages and/or disadvantages of vortex evolution are studied by the correlation between the internal vortex evolution and the bulk flow parameters related to hydraulic loss in elbow outlet conduit, based on which the relationship between geometric parameter and vortex evolution pattern is established accordingly. Using a steady or quasi-steady flow model, an optimal design can be achieved for minimizing the hydraulic loss based on meticulous choice of geometric parameters. The purposes of this project are to reveal the dynamics (generation and evolution) of Dean vortex flow in elbow conduit under a broad range of flow and geometrical conditions, and to achieve effective control of Dean vortex and hence to propose a new Hydraulic Optimization Design Method for elbow outlet conduit.

降低弯肘形出水流道水力损失是提高低扬程泵站装置效率急需解决的关键问题，而揭示流道内部二次流损失机理并提出流动控制方法是改善其水力性能的基础研究。本项目首次引用Dean涡流动理论，采用数值计算和PIV试验相结合的方法研究不同几何参数和环量影响下流道内Dean涡的演变规律；利用性能试验获得流道水力损失变化规律，结合涡核速度特征法对流场进行分析诊断，构建入口扰动引起的流动失稳特征与流道水力损失的映射关系；基于演变涡与流道水力损失相关的流动参数之间的关联性对演变涡的利弊特性进行研究，建立不同几何参数与对应演变涡的映射关系；依据定常或准定常的流动模型，通过几何参数的精心设计，达到流道水力损失最小的优化目标。本项目研究旨在揭示几何参数和环量对Dean涡流动损失机理的影响，实现Dean涡流动的被动控制，创新弯肘形出水流道水力优化设计方法。

降低弯肘形出水流道水力损失是提高低扬程泵站装置效率急需解决的关键问题，而揭示流道内部二次流损失机理并提出流动控制方法是改善其水力性能的基础研究。本项目在理论分析层面，首次在低扬程泵站弯肘形出水流道内引入Dean涡理论，揭示了几何参数和入口流动参数对弯肘形出水流道内Dean涡的发展演化规律及其水力损失影响机理，建立并发展了涡核速度特征法成功捕捉了Dean涡不稳定性，初步揭示了二次流强度与流道水力损失的映射关系。在设计方法层面上，基于Dean涡理论对弯肘形流道几何参数进行数学描述，推导并拟合了弯肘形流道的曲率比和面积比随流道沿程变化的函数关系式，建立了基于Dean涡理论的弯肘形出水流道水力设计方法，为高效可靠的流道水力模型开发提供了新方法。在技术应用层面上，开展了多个弯肘形出水流道泵装置水力性能综合试验，通过能量特性曲线获得了不同叶片安放角运行时泵装置的流量、效率、轴功率和流道损失等模型试验数据，证明了弯肘形出水流道型线设计优化和水力模型选择合理，研究成果已成功应用于凤凰颈新站、阚疃南站、江庄提水泵站等多个大中型水利工程和农业灌排工程用泵站，取得了显著经济效益和社会效益。