Author(s): C. Polatel
Linked Author(s):
Keywords: Open channel flow; Free surface velocity; Indexing; Laser Doppler Velocimetry (LDV); Large Scale Particle Image Velocimetry (LSPIV); Sand dunes
Abstract: Discharge estimation is the essential part of any hydraulics problem related with rivers, such as sediment or pollutant transport. Traditional methods that are used to determine river discharge have many shortcomings. A non-contact method with lower cost, better accuracy, and less hazards than that of traditional stream-gauging method is currently being investigated. One of these methods, called “indexing”, aims to plot all the velocity profile for known bed characteristics by using only one pointwise velocity measurement. The essential part of this method is to estimate the non-dimensional velocity distribution for given bed characteristics. Having the structure of the velocity distribution, only one pointwise velocity measurement will be enough to plot velocity profile. Taking the free surface velocity as indexing velocity has advantages in the aspect of appropriateness to non-contact measurement techniques. However, both free surface velocity and velocity profile are sensitive to many factors including the bed characteristics. From the perspective of the non-contact, remote measurements of the free surface, the effects of related parameters on the free surface velocity and velocity profile have become an important issue to be investigated. Here the summary of some preliminary results related to this topic obtained from the ongoing studies at IIHRHydroscience and Engineering laboratories are presented. Among the parameters involved, bedform effect is discussed in this paper. Two tests, one for the flow on smooth straight channel bed and the other for the flow over sand dunes, are presented. The results of the observations show that there is a signature of the spatial changes in the channel bed on the free surface velocity. The quantitative description of this signature is left as a future work for the subsequent publications.
Year: 2003