Author(s): Shuen-Jong Tsorng; Guan-Ru Chen; Jihn-Sung Lai; Yih-Chi Tan
Keywords: Free overfall; Laser-sheet imaging technique; Periodic oscillatory flow
Abstract: In this study, water stage of free overfall flow with a plunge pool in a rectangular flume (B=20 cm) is measured using point gauge and laser-sheet imaging technique. Single approaching flowrate Q i =2620cm 3 /s, constant drop height h d =11 cm and fixed sill height h s =5 cm are given. The length of plunge pool is considered in the range of L p =5-30 cm. The laser-sheet imaging technique show good performance to accurately profile the oscillating free water surface. The flow field of skimming and napped flow are described and the range of the plunge pool length is defined, 14.5≤L p ≤20.5 cm. Skimming and napped flow conditions alternatively emerge at a constant period in the periodic oscillatory flow. From water stage histories, the oscillatory pattern is not only found in the plunge pool, but also at the upstream side of drop. The water stage amplitude also gradually disappears as measurement position far from the pool. To expand the application of end-depth method, a check is then carried out. The mean end depth of periodic oscillatory flow is still suitable for flowrate estimation.