Abstract
Contracted flows caused by short hydraulic structures (length L/depth H=2.5–20) were extensively analysed by previous investigators. However, flows narrowed by long cofferdams (L/H>20) have neither been thoroughly examined nor well understood. In this study, a series of simulations were conducted by using a plane two-dimensional numerical model to analyse the influence of a cofferdam on flows in a narrowed channel and to evaluate the effects of the contraction ratio, longitudinal cofferdam length and cofferdam angle on the flow field. The model was developed with the finite-volume method and was validated by using laboratory flume measurements. Simulation results and analyses show that the cofferdam significantly affects the flow field and that the contraction ratio has a greater effect on flow characteristics in the narrowed channel than the longitudinal cofferdam length and cofferdam angle. This study assists in the better understanding of the impacts of cofferdam on the flow field and provides useful information in cofferdam design for multi-staged diversion during the construction of hydraulic projects.
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