Abstract: Obstacles on the bed have important impacts on the hydrodynamic behaviors of gravity currents in hydraulic engineering. In this paper, a high-speed camera and a laser particle image velocimetry (PIV) technique were applied to investigate the characteristics of lock-exchange gravity currents encountering different obstacles at the slumping stage on a flat bed. The experimental results show that the obstacle influenced the head velocity of gravity currents within about 5-lock length, while the reduction of maximum speed of the head before meeting the obstacle was small, with a value of about 1%. When the thickness of the gravity current was equal to the height of the obstacle, the maximum height of the gravity current on the environment may be nearly doubled. In the same condition, the height caused by the rectangular obstacle was about 20% larger than that by the triangle one. The time for the peak thickness of the gravity current at three characteristic sections (i.e. in front of, behind, and on the top of the obstacle) varied from 1.5 to 2s later than that for the energy. The energies at the characteristic sections in front of and behind the obstacle followed a unimodal distribution, while that at the top section followed a bimodal distribution. The peak thickness at the characteristic sections in front of the obstacle increased about 20%, but the peak energy decreased about 40%. The present results provide useful information for pollutant in water environment, submarine cable protection, and reservoir deposition, etc.

Key words: gravity current, obstacle, particle image velocimetry (PIV), velocity field, vorticity field