Author(s): Chunjing Liu; Wenhong Cao; Linjuan Xu; Danxun Li; Xingkui Wang
Keywords: Shear Velocity; Unsteady; Open Channel Flow; Flume Experiment
Abstract: Shear velocity is one of the most important parameters for analyzing the friction properties and sediment transport in open channel flows. The aim of this study is to evaluate 4 different methods for estimating the friction velocity in unsteady open channel flows. Six runs of unsteady flow experiments with different unsteadiness were carried out in a flume with a smooth bed. The discharge and water level were measured in each test. The Instantaneous velocities were measured by a two-dimensional LDA system. Time dependent friction velocities during the ascending and descending unsteady flows of each runs were determined from four different approaches, namely the Saint-Venant equation method, the log-law method and the Reynolds stress method, and the steady flow method. The results calculated from each run of the experiments showed that the unsteadiness of the flow would have strong effect on the shear velocity estimation. The reasonable friction velocity could be obtained by using the log-law and Reynolds stress approach for all of the six runs of test. But the Saint-Venant equation method was failed for the sharply changing unsteady flow.