Effects of Bottom Obstacle Structure on Density-Induced Flow

Abstract

Density flows frequently occur in nature and some of them have caused serious consequences, such as sedimentation and saline water intrusion. In order to control density flows, the method like placing an obstacle has been proposed. In this paper, the influence of the height and position of obstacle and the salinity difference on the behaviors of lock-exchange density flow was studied experimentally by using high-speed camera and laser particle image velocimetry (PIV) technique. The experiments were conducted in a plexiglass flume whose height, width and depth were 1.8 m, 0.22 m and 0.3 m respectively. Besides, the bottom of the flume is smooth. The flume was separated by one board and the left side of the flume was filled by fresh water while the right side of the flume was filled by salt water. After the board was lifted, the salt water flow into the fresh water and formed a density flow. Obstacles were placed 0.05 m and 0.25 m away from the gate respectively. The velocity and flow field were measured by using the PIV technique. The results indicated that the existence of obstacles blocked the progress of density flow and the propagation distance of density current in the case without obstacle was much longer than the other one which contained obstacle. Additionally, it was observed that when the density flow was crossing over one obstacle, a re-acceleration process was happening at the head of the current, and the maximum velocity caused by this process was larger than the maximum velocity without obstacles. Besides, by comparing the obstacle and non-obstacle situations, the body velocity of density flow was greatly reduced at the front of obstacle. However, the effect of different obstacle positions on the maximum velocity of the head of density flow is not significant.