The transverse water surface slope and secondary flow are main hydraulic features of bend flows, which are the result of the interaction between the gravity and the centrifugal force in bend flows. The hydrodynamic characteristics of bend flows such as the water surface slope, the longitudinal velocity, the transverse circulation, the turbulence kinetic energy and the intensity of secondary flow vary with the water depth in downstream. A series of flume experiments were conducted in a U-shape bend to study these hydrodynamic characteristics. Results show that the water surface slope, the longitudinal velocity, the turbulence kinetic energy and the intensity of secondary flow generally decrease with the increase of downstream water depths. The decline appears to be uneven in different sections of the bend. The results are favorable to further study on the effect of backwater to the structure of bend flows.
采用U形弯道模型,研究在弯道出口顺直段上建坝及不同坝高对水流纵向流速分布特性的影响。试验结果表明:在弯道上建坝后水流的纵向流速变小,且坝越高流速越小,坝前顺直段流速偏离系数增大;高坝对弯道流速沿程变化规律的影响比低坝大;建坝后弯道水流的流速分布比无坝时更均匀对称;低坝对水流纵向流速在垂线上分布规律的影响不大,高坝会使纵向流速在垂线上的变幅减小。
The characteristics of flow motion in a U-shape bend after a sluice construction were studied through flume experiments.The experimental results show that there are obvious changes of water levels at the convex and concave sides and the center line of the bend before and after constructing a sluice.It results in gentle transverse gradient of water surface,smooth dynamic axis of flows and uniform distribution of flow velocity.It is in favor of deeply analyzing the characteristics of flows in bends with sluice construction as well as the influences on sediment motion and riverbed evolution,etc.
The structure of an U-shape bend flow including lateral slope of water surface,streamwise velocity,circulation flow and typical u-v vectors along water depth directions were analyzed.Velocities were measured using up-looking and down-looking Sontec-ADV(acoustic doppler velocimenters).Furthermore,the numerical modeling of bend flow has also been conducted in the experimental flume under various flow conditions.These simulated results agree well with the experimental data.
