| Summary: | 碩士 === 國立中興大學 === 土木工程學系所 === 96 === The characteristics of skimming flows over a vertical drop were investigated experimentally using visualization technique and high speed particle image velocimetry (HSPIV) system. The non-dimensional critical depth (Yc/H) ranges from 0.335 to 0.632. According to the result observed qualitatively by using visualization technique, the flow region can be divided to sliding jet and pool regions. The flow fields were measured and discussed for these two regions.
First the study aims at sliding jet. According to digital image and water surface profile measured by point gauge, the curve of water surface can be determined by multi-variable regression. In order to measure the velocity of shear layer, curvilinear coordinate used instead of cartesian coordinate. The velocity profiles were measured from upstream to downstream. Based on the result, the shear layer thickness increases as the sliding jet moves downstream. Using the method proposed by Lin et al. (2008), the velocity profiles can be established by the center point of shear layer, Yrc, the specific width, bs, as length scale and the velocities of the upper and lower boundary of specific width Uu and Ud, as velocity scale., the similarity profile of shear layer was obtained as following:(略)
The study also focuses on the characteristics of pool region. The shape of velocity profiles in the pool is similar to a wall jet. Different characteristic values were tested for velocity and length scales for similarity analysis. Finally, by selecting the maximum adverse velocity Um as velocity scale and half-width thickness b0 as length scale, similarity profile can be obtained in the form of:(略)
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