Characteristics of upwelling of hollow square enhancement reefs based on particle image velocimetry

Abstract: Based on particle image velocimetry (PIV), the upwelling characteristics of hollow square enhancement reefs was researched, including the upwelling scale of a single reef under different flow velocity, the influence of reef deployment to upwelling, and the upwelling change with different arrangements of reefs. The real size of the reef was 800 mm in length, 800 mm of height 400 mm in width, and a hole in the reef was 200 mm in length, 200 mm in height, and the thickness of the reef was 40 mm. The real flow velocity (0.2, 0.4, 0.6, 0.8 and 1.0 m/s) and depth of the ocean were measured, According to the similarity principle, the experiment velocities were 0.045, 0.090, 0.135, 0.180, and 0.225 m/s. The experiment results indicated: when the deployment of a single reef is the same, the scale of upwelling became strong as the flow velocity increased. Under the same velocity, the upwelling scale of the main surface against the flow was the largest, the velocity maximum of the upwelling was 62% of flow velocity. The velocity maximum of the upwelling of the side surface and top surface with 90° against the flow was between 30% and 40% of the flow velocity. The upwelling scale of the top surface with 45° against the flow was the smallest, and the velocity maximum of the upwelling was only 14 percent of the flow velocity. Analysis showed that the deployment of the reef had an important effect on upwelling characteristics. As area against the flow became larger, the upwelling scale became apparently stronger. Under the same velocity, the ratio between the upwelling height and reef height of the top surface with 90° against the flow was higher than the others, which did not have a direct proportion with the reef height, and in order to measure the stability of the reefs, the deployment of the top surface with 90° against the flow was chosen, which arrangement of different distance was researched. When the distance between the reefs arranged horizontally was 0.5L, the area and height of the upwelling was the largest. When the distance between the reefs arranged horizontally was 1.0L, the velocity maximum of the upwelling was obtained. When distance between reefs arranged horizontally is 2.0L, upwelling area is smaller than single reef's. When the distance between the reefs arranged horizontally was 1.5-2.0L, the upwelling height was smaller than a single reef's. So when the distance between the reefs arranged horizontally was from 0.5L to 1.0L, the interaction of reefs was strong, and the scale of the upwelling became larger. When the distance between the reefs arranged longitudinally was 1.0L, the velocity maximum of the upwelling was obtained. When the distance between the reefs arranged longitudinally was from 0.5L to 1.5L, the area and height of the upwelling was larger than the single reef's. So when the distance between the reefs arranged longitudinally was from 0.5L to 1.5L, the interaction of the reefs was the largest. According to the experiment's result, the configuration of the reefs was designed, every unit was constituted by 100 reef, the reef was deployed as a top surface with 90° against the flow, and the distance between the reefs arranged horizontally with flow was 1.0L, and the distance between the reefs arranged longitudinally with flow 1.5L.