Experimental study of flow structures of a solitary wave over two rectangular tandem obstacles

In this research, interactions between a solitary wave and two submerged rectangular obstacles with different distances were studied experimentally. The particle image velocimetry (PIV) technique was used to measure the velocity field on the weather and lee sides of the two obstacles. Two submerged rectangular obstacles with 12-cm height and 8-cm length were installed in an open water channel with 7-m length. The velocity fields were obtained with 5 fields of view (FOVs) and then synchronized together. The vortices that formed on the weather and lee sides of the rear and front obstacles were compared to each other. It was found that the vortex on the weather side of the rear obstacle was flatter and smaller than that on the weather side of the front obstacle. Moreover, the weather-side vortex of the front obstacle grew more. After the wave passes over the two obstacles, the vortices on the weather and lee sides of the front obstacle are merged together and form a larger vortex. A higher vorticity at the center of the weather side vortex of the front obstacle was observed. By increasing the distance between the obstacles, the vortex between the obstacles expands more, and the interaction of the flow with the obstacles is more intensive so that more and larger vortices are formed. These vortices depreciate the wave energy. The measurement of the wave height before and after the obstacles showed that the larger the distance between the obstacles, the higher wave energy loss will be.