Effects of Two Consecutive Obstacles on Gravity Currents Dynamics

Abstract:

The phenomenon of gravity current exists widely in natural environments and hydraulic engineering. In practical conditions, the obstacle is an effective mean to prevent the invasion of gravity current, so it is valuable and worthwhile to study the effects of obstacles on the dynamic characteristics of gravity current. In this paper, the lock-exchange experiments were carried out to compare the maximum diffusion height and head velocity of gravity current with different obstacle conditions, and the optimal obstacle layout for the engineering application can be therefore obtained. In addition, the velocity profiles in the upstream and downstream of the obstacles, the vorticity field of gravity current over the obstacles, and changes in the entrainment coefficient of gravity current along the channel were analyzed. The results show that for the optimal engineering layout scheme of consecutive obstacles is as follows: the first obstacle needs to be higher than the second obstacle, and the distance between two obstacles should be as large as possible, but the typical head shape of gravity current should not be restored before it meet the second obstacle. In the upstream of the first obstacle, the velocity profiles is disturbed and decreased, and the disturbed range is approximately equal to the height of the obstacle. In the downstream of the second obstacle, there are obvious wall region and jet region in the velocity profiles of the gravity current. Compared with the condition of no obstacle and single obstacle, the thickness of the gravity current flowing through the two obstacles decreases obviously. When the gravity current flows over obstacles, the current entrainment coefficient presents an "M" type distribution. The entrainment coefficient of gravity current over the second obstacle is greater than that in the first obstacle. The conclusion of the study can provide scientific basis for mitigating the hazards induced by gravity current and ensuring the safety of hydraulic infrastructures.