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Turbulent Structures and the associated sucliment transport

湍流结构和相关的水分输送

基本信息

批准号：
05555144
负责人：
NAKAGAWA Hiroji
金额：
$ 9.98万
依托单位：
KYOTO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Developmental Scientific Research (B)
财政年份：
1993
资助国家：
日本
起止时间：
1993 至 1994
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-05555144/
关键词：
Turbulence Unsteady Flow Open Channels Laser Doppler anemometer Particle-Tracking Velocimetry Compound Open Channel Flows PTV FLDA 流れの非定常効果

项目摘要

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.

采用双分量LDA系统和水波计同时进行了非定常明渠光滑壁面湍流度的精确测量。在洪水上升和下降阶段，壁面区域都能很好地满足“一般”对数分布，其中von Karman常数是k=0.41的通用对数分布，而积分常数A是主流条件的函数。另一方面，对数尾流规律在包括变深区在内的外部区域得到了合理的应用。高斯尾流参数PI在上升阶段增大，在下降阶段减小。除了非常接近自由表面外，上升阶段的湍流比下降阶段更强。随水面变化的明渠流动的非定常特性与封闭管道流动的非定常特性有很大不同。特别有意义的是在非定常明渠流动中速度和湍流度随深度变化的逆时针循环的发现。接下来，在进一步的研究中，使用高灵敏度CCD相机和2W氩离子激光狭缝照明技术，在视盘上记录了均匀悬浮在复合明渠流动中的非常小的100 μ m直径颗粒的图像。在激光狭缝平面上每一点的瞬时速度由这四个连续的粒子图像测量得到。这种被称为“粒子跟踪测速（PTV）”的新技术，由于可以在水流的任意截面上的所有网格点同时获得速度分量，因此利用速度分量的象限运动的条件采样方法来研究湍流相干涡的时空相关结构似乎是非常强大的。