【作者】 王殿常；

【导师】 王兴奎； 邵学军；

【作者基本信息】 清华大学 ， 水力学及河流动力学， 2000， 博士

【摘要】 明槽紊流近壁区的颗粒运动与紊动猝发现象及紊流相干结构有着密切的关系，开展近壁区颗粒与紊流相互作用的机理研究对于流体力学和泥沙运动力学都有着重要的理论意义和实际价值。本文以试验研究为主要手段，采用流动显示和图像处理技术，从水槽底部和侧面两个方向测量，分别对明槽紊流近壁区的带状结构及颗粒运动特性进行了系统的试验研究。基于流动显示和图像处理技术，独立开发了明槽紊流近壁区带状结构的实时测量系统。利用该系统可获取大量的统计样本并进行计算机快速分析，为明槽紊流相干结构的试验研究提供了一种崭新的测量手段；在前人工作的基础上，开发了一种能够测量水流中颗粒运动轨迹的PTV系统，该系统具有可靠的精度，能同步测量全剖面的颗粒瞬时运动信息，为颗粒运动特性及动力学特性的试验研究提供了强有力的手段。在水力光滑区和过渡区对明槽紊流近壁区的带状结构进行试验，测量并分析了带状结构的分布，首次揭示出低速带间距、宽度、纵向尺度及持续时间等随摩阻雷诺数的变化规律。试验结果表明，低速带间距的无量纲数λ+并非为以往一致认为的100左右的常数，而是随摩阻雷诺数的增大而逐渐增大，在水力光滑区与摩阻雷诺数成二次方关系，在过渡区则为线性关系。低速带间距的概率密度分布可用对数正态分布来描述。低速带宽度、纵向尺度及持续时间等随摩阻雷诺数的变化规律与低速带带间距的变化规律类似。低速带宽度在水槽中心位置最大，往两边的边壁逐渐减小，而且在横向上相对于水槽中心线对称分布。低速带间距与宽度的比值约为2．0。对带状结构的产生过程进行了试验，对其产生机理提出了一种横向涡模型，该模型能够对带状结构的空间分布规律进行定量解释。对轻质沙和重颗粒在明槽水流中的运动特性进行试验，明确提出了颗粒运 。如文摘gb山轧；抓山二川it本类型，即L升、下降和平移，颗粒以不问类刑…力；对其协力，｝特上2－uV个问。按照三种基本类型对颗粒的运动细节进行划’1。个均分析，g．’i人在u，U；，；＞U；，；；＞U；，；；。轻质颗粒向下的运动速度明显大于其在静水’上的沉速，出重颗粒则相反。颗粒纵向平均运动速度沿垂线的分个基本服从对数规律，卡门常数的取值范围为0．29～0．43，积分常数有较大的变化范围。厂 利用实测资料分析了颗粒所受综合升力沿垂线的分布规律，结果表明，综合升力与｝川成反比关系；基于颗粒运动的力学机理，提出了“颗粒的上升速度刚好等于其沉速时表示推移质开始向悬移质转化”的观点，在此基础上推导得出了推移质向悬移质转化高度H。。所满足的方程式。更多还原

【Abstract】 For dilute solid-liquid two-phase flow, the mechanism of particle motion driven by fluid is the main subject, especially the particle motion in the near wall region. The bursting phenomenon and coherent structure of turbulence play an important role on the motion of particles in the near wall region. Therefore, studies on the interaction between particles and turbulence are of essential significance for fluid mechanics and river dynamics. In this paper, the spatial structure of the low-speed streaks and particle motion in the near wall region of turbulent open channel flow were observed on the side and bottom of a water flume, respectively, using flow visualization and image processing techniques.A measurement system was developed based on flow visualization and image processing techniques, which can be used to investigate the spatial structure of low-speed streaks in the near wall region of turbulent open channel flow. A large number of data can be collected using this system because of the real-time sampling on the computer. It is a reliable instrument for the measurement of the coherent structure in turbulence. An improved 2-D PTV was developed based on previous research experiences, which can be used to measure the trajectories of particles motion. For the experimental study on the particle motion in the dilute solid-liquid two-phase flow, especially for the motion characteristics and dynamic characteristics of coarse particles in water, this kind of system was proved to have great advantages.A series of experiments in a wider range of Reynolds number were conducted for the investigation on the spatial and temporal distribution of the low-speed streaks in the near wall region of turbulent open channel flow. For the first time, the relationships between the spacing, the width, the length scale in the streamwise direction and the duration time of low-speed streaks and the Reynolds number based on shear velocity were revealed. The present results indicate that the quantitative description of the non-dimensional mean lateral streak spacing + differs from the results previously published. The spacing + is not a constant value of 100. It becomes larger as the Reynolds number in terms of shear velocity increase. In the smooth regime the spacingincreases with the quadratic power of Re., but has a linear relationship with Re, inthe transitional regime. The dividing point is located at about Re, = 900 . The probability density distribution of + conforms to the lognormal behavior. Thevariation of the width, the length scale in the streamwise direction and the persisting time of low-speed streaks with Re, have similar relations to the spacing.The distribution of streak width along the lateral direction shows that the width attains its maximum value at the central line and becomes narrower toward the side wall, and its distribution is symmetrical about the central line of the flume. The ratio of the streak spacing to the width is about 2.0, which implies that the high and low speed streaks takes up almost the same space in the lateral direction. A special experiment was performed to investigate the formation process of streaks. A new vortex model was presented to interpret some experimental results in present work based on the mechanism of streaks production.A series of experiments on the motion characteristics of light polystyrene particles and heavy glass particles were carried out in open channel flow. The test results show that it is essential to divide the particle motion into three typical types that is rising, falling and translating motion, because the motion characteristics and dynamics characteristics are apparently different when the particles moving in different types, especially in the near bed region of the open channel flow. The mean velocity profile ofparticles in streamwise direction follows the log-law, namely U p = Kp lny+ + Bpwith KP = 0.29 ~ 0.43 . The value of Bp is dispersed. The particle velocity instreamwise direction as the particle rise is larger更多还原