Turbulent Structures and the associated sucliment transport

本文利用双分量激光多普勒测速系统和水波计同时测量了明渠非恒定流中光滑壁面上的湍流。“一般”对数律分布，其中冯卡门常数是普遍的k=0.41，但积分常数A是一个函数的主流条件，满足以及在壁区的上涨和下跌阶段的洪水。另一方面，对数尾流定律被合理地应用于包括深度变化区在内的外部区域。Coles尾流参数PI在上升段增大，而在下降段减小。上升段的湍流比下降段的湍流强，除了非常靠近自由表面的区域。这些非定常特性在变水面明渠水流中与在封闭管道水流中有很大的不同。特别重要的是逆时针循环的速度和湍流对变化的深度在不稳定的明渠flow.Next，在进一步的研究中，非常小的100妈妈直径的颗粒均匀悬浮在复合明渠流的图像记录在光盘上使用高灵敏度的CCD相机和2W氩离子激光狭缝照明技术。在激光狭缝平面中的每一点的瞬时速度测量从这些连续的四个图像的一个粒子。粒子跟踪测速技术（PTV）是一种新的测量湍流相干涡时空相关结构的方法，它采用速度分量象限运动的条件采样方法，可以在水流任意截面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.