American Society of Civil Engineers


Characteristics of Shear Layer Structure in Skimming Flow over a Vertical Drop Pool


by Wei-Jung Lin, (Postdoctoral Research Fellow, Center for Environmental Restoration and Disaster Reduction (CERDR), National Chung Hsing Univ., Taichung 402, Taiwan. E-mail: linweijung@gmail.com), Chang Lin, (corresponding author), (Professor, Dept. of Civil Engineering, National Chung Hsing Univ., Taichung 402, Taiwan E-mail: clin@mail.nchu.edu.tw), Shih-Chun Hsieh, (Postdoctoral Research Fellow, Dept. of Civil Engineering, National Chung Hsing Univ., Taichung 402, Taiwan. E-mail: iraqkimo@yahoo.com.tw), Chien-Chuan Li, (Graduate student, Dept. of Civil Engineering, National Chung Hsing Univ., Taichung 402, Taiwan. E-mail: leecc1982@gmail.com), and Rajkumar V. Raikar, (Professor, Dept. of Civil Engineering, K. L. E. S. College of Engineering and Technology, Belgaum 590008, India. E-mail: rvraikar@gmail.com)

Journal of Engineering Mechanics, Vol. 135, No. 12, December 2009, pp. 1452-1466, (doi:  http://dx.doi.org/10.1061/(ASCE)EM.1943-7889.0000050)

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Document type: Journal Paper
Abstract: The characteristics of shear layer structure between the sliding jet and the pool for skimming flows over a vertical drop pool were investigated experimentally, using flow visualization technique and high speed particle image velocimetry. Four series of experiments having different end sill ratios (h/H=0.12, 0.43, 0.71 and 1.0, where h=end sill height and H=drop height) with various approaching flow discharges were performed to measure the detailed quantitative velocity fields of the shear layer. The mean velocities and turbulence properties were obtained by ensemble averaging the repeated measurements. From the velocity profiles, it is found that the growth of the shear layer in the downward direction as the jet slides down the pool represents the momentum exchange. Analyzing the distribution of measured velocity, the similarity profile of the mean velocity at different cross sections along the shear layer was obtained. The proposed characteristic scales provided unique similarity profiles having promising regression coefficient. The selection of these characteristic scales is also discussed. Further, the spatial variations of mean velocity profiles, turbulence intensities, in-plane turbulent kinetic energy, and Reynolds shear stress were also elucidated in detail. The imperative observation is that the Reynolds shear stress dominates the major part along the shear layer as compared to the viscous shear stress. The study also provides an insight into the flow phenomena through the velocity and turbulent characteristics.


ASCE Subject Headings:
Drop structures
Flow measurement
Layered systems
Velocity