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http://dx.doi.org/10.3741/JKWRA.2005.38.11.917

Estimatation of Mean Velocity from Surface Velocity  

Roh, Young-Sin (Korea Institute of Construction Technology)
Yoon, Byung-Man (Dept. of Civil & Environmental Eng., Myongji Univ.)
Yu, Kwon-Kyu (Dept. of Civil & Environmental Eng., Myongji Univ.)
Publication Information
Journal of Korea Water Resources Association / v.38, no.11, 2005 , pp. 917-925 More about this Journal
Abstract
LSIV (Large Scale Image Velcocimetry) Is one of the image-based velocity measurement techniques. Since it measures surface velocities, it gives simple and inexpensive way to measure velocity, compared to other methods. Because of these advantages, there have been many studies to apply LSIV to the river discharge measurement in the field. Measuring the discharge by using LSIV requires a method which converts a surface velocity to a mean velocity In the present study, experiments and analysis of vortical velocity profile of open-channel flow in various conditions were performed to develop methods which estimate a mean velocity from a surface velocity. The result of this experiment reveals that velocity-dip phenomena occur at free-surface layer in open channel flow and Froude number affects more than bed roughness does. Two methods for estimating the mean velocity were proposed. One is to correct the wake law's profiles by using the difference of surface velocity from the mean velocity, and the other is to use the ratio of mean and surface velocities. The result of applying these methods in an experiment shows that they are quite accurate having an error of approximately $6\%$ only.
Keywords
LSIV; surface velocity; mean velocity; velocity-dip phenomena;
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