Turbulent Structures and the associated sucliment transport

为了准确测量明渠非恒定流中光滑壁面的湍流，同时使用双分量激光测距系统和水波测量仪。其中von Karman常数是k=0.41的普适对数分布，而积分常数A是主流条件的函数，无论是涨落洪水，都能很好地满足“一般”对数定律分布。另一方面，对数尾迹定律被合理地应用于包括变水深区域在内的外部区域。科尔斯尾迹参数PI在上升段增大，在下降段减小。除了非常接近自由面外，上升段的湍流比下降段的湍流更强。变水面明渠水流的这些非定常特性与闭合管道水流的非定常特性有很大的不同。其次，在进一步的研究中，利用高灵敏度的CCD摄像机和2W激光狭缝照明技术，在光盘上记录了直径为100微米的微小颗粒均匀悬浮在复合明渠水流中的图像。从这四幅连续的一个粒子的图像中测量了激光狭缝平面上每个点的瞬时速度。这项名为“粒子跟踪测速(PTV)”的新技术对于用速度分量象限运动的条件采样法研究湍流相干涡旋的时空相关结构似乎是非常有效的，因为它可以在水流任意截面处的所有网格点上同时获得速度分量。

Turbulence measurements over smooth wall in unsteady open-channel flows were conducted accurately by the simultaneous use of two-component LDA system and waterwave gauges. The "general" log-law distributions in which the von Karman constant is universal one of k=0.41 but the integration constant A is a function of main-flow conditions, were satisfied well in the wall region for both the rising and falling stages of flood. On the other hand, the log-wake law was reasonably applied to the outer region including the depth-varying zone. The Coles'wake parameter PI increased for the rising stage, whereas it decreased for the falling one. The turbulence is stronger for the rising stage than for the falling one, except for very near the free surface. These unsteady characteristics in open-channel flows with varying the water surface are quite different from those in closed duct flows. Of particular significance is the findings of counterclockwise loop of the velocity and turbulence against the varying depth in unsteady open-channel flows.Next, in the further study, images of very small 100 mum diameter particles uniformly suspended in compound open-channel flows were recorded on an optic disc using a high-sensitive CCD camera and 2W Argon-ion laser slit illumination techniques. Instantaneous velocities at each point in the laser slit plane were measured from these continuous four images of one particle. This new technique called the "Particle-Tracking Velocimetry (PTV)" seems to be very powerful to investigate space-time correlation structures of coherent vortices of turbulence using the conditional sampling method of quadrant motions of velocity components because simultaneous velocity components can be obtained at all grid points of arbitrary section plane of water flows.