平面大扩散角明渠流均衡过渡机理与三角翼调控方法

Due to the limitation of site, many water conveyance projects have no choice but to take the plane diffusing reach with large angle as a transitional connecting form. Problems will occur in diffusing reach, such as flow separation, backflow and bias current, which have adverse influence on the discharge security. Measures must be taken to control the separation of boundary layer so that flow transition can be smooth. Characteristic of flow field at different flow regimes, process of separation of boundary layer and characteristic of separation in diffusing reach with large angle are studied by the methods of a series of hydraulic scale model tests and three-dimensional numerical simulation. Critical condition of losing stability and regulation mechanism of flow are studied by using two-dimensional balance degree and separation degree of boundary layer. The adjustment of the momentum of flow field due to influence of intervention and critical index of equilibrium are studied by appling PIV technology and turbulent coherent analysis. Besed on the theory of adjustment of momentum distribution and restriction of boundary layer, the method of setting up submerged delta wing in diffusing reach is proposed to control flow and separation of boundary layer. Model is built based on κ-εturbulent pattern. The relation of hydraulic characteristics of submerged delta wing and equilibrium of flow field in the diffusing reach is studied. The index of the comprehensive control and application condition in regard to the setting of delta wing are seeked. The method of design of delta wing that meets the requirement of equilibrium transition is put forward. The technical problem of smooth transition in diffusing reach with large angle is solved and the theory of controlling flow and restriction of separation of boundary layer are extended.

许多输水工程因空间限制，需采用大扩散角明渠过渡衔接；过渡段会出现水流脱离边界、侧壁回流、偏流现象，影响泄流安全。要实现水流平顺均衡过渡，须对扩散段边界层分离采取有效抑制措施。采用系列水力模拟与流场三维数值仿真相结合的方法，研究大扩散角明渠过渡段不同流态的流场特征、边界层发展及分离特性，引入二维均衡度、边界层分离度，探寻扩散水流失稳临界条件与调控机理。应用PIV技术和湍流相干分析，研究介入干扰对扩散段流场动量调整的影响机制与均衡性临界指标；基于动量调控分配及边界层胁迫限制理论，提出在扩散段内设置潜没三角翼调控水流，抑制边界层分离的方法。基于κ-ε湍流模式构建模型，研究潜没三角翼体的水动力学特性与扩散段流场均衡性的关系，探寻扩散段内设置潜没三角翼的综合控制指标与适用条件，给出满足水流均衡衔接要求的三角翼设计方法。解决明渠大扩散角过渡段水力设计的技术难题，拓广扩散水流调控及边界层分离限制理论。

流体输送工程通常会遇到明渠大扩散角过渡段的水流衔接问题，为解决过渡段偏流与回流产生影响泄流安全，必须采取减小扩散角延长过渡段的方法或者采用辅助工程措施调控水流抑制偏移；无论是从节约空间的工程应用角度还是从控制边界层分离的理论层面，都需要开展对大扩散角明渠过渡段水流特征及控导机理的研究。本研究以常见水利工程实际问题为研究背景，选择典型研究对象，采用系列水力模拟试验与流场三维数值仿真相结合的方法进行了系统研究。首先对一般大扩散角无控导过渡段不同流态的流场特征、边界层发展及分离特性开展了研究，建立了扩散段三维水动力模型和不同尺度的扩散段水槽试验模型；应用PIV技术和湍流相干分析，研究探寻了扩散段水流结构及水流失稳机理，给出了诱发干扰与偏流趋势的响应关系。在扩散段内设置抑制边界层分离的潜没三角翼，对扩散段水流进行调控模拟研究；探索了三角翼介入干扰对扩散段流场水流结构的影响机制以及下游的调整规律，根据流速及动量调整特征建立了三角翼作用下的扩散段马鞍型水流稳态模式，阐述了潜没三角翼体水动力学特性及其与扩散段新均衡稳态流场的响应关系，在此基础上得到了扩散段内三角翼控制指标，提出了控制指标与扩散段水流边界条件的对应关系及优化方法，给出满足水流均衡衔接要求的三角翼技术参数和设计流程；研究成果拓广了扩散水流调控理论及边界层分离抑制方法，为解决明渠大扩散角过渡段水力设计理论提供了技术支撑。