Study On The Flow Field Around The Hexagonal Artificial Reef

Artificial reefs are one of the main artificial structures used in the construction of marine pastures,often using open-hole shaped concrete structures or framed steel structures,placed on the seabed to simulate natural reefs,providing a good habitat for marine life,protecting and increasing fish production,and restoring and transforming the original marine ecological environment.The artificial reefs will be subject to natural hydrodynamic factors such as currents and waves,and will have an impact on the flow field around the original area.Firstly,the artificial reef will act as a barrier to the current and a local upward flow will be formed in front of the reef.The upward flow will bring nutrients from the bottom to the upper waters,promoting the exchange of nutrients between the upper and lower waters and increasing the nutrient concentration in the waters around the reef area,which is conducive to fish gathering and feeding.Secondly,the current will form a certain range of slow flow area behind the reef.The Slack flow region in this zone helps to deposit nutrients and provides space for fish to live and breed.The performance of artificial reefs in changing the surrounding hydrodynamic state is called the "flow field effect".Most of the research on artificial reefs at home and abroad is focused on reefs in the form of concrete openings,while the flow field effect of existing artificial reefs is far from ideal and has a large impact on the natural hydrodynamic environment.The development of new forms of reefs with high quality flow field effect and minimal impact on the hydrodynamics of the released area has become one of the important research problems in the construction of marine pastures.This paper investigates the flow field effects of a new type of reef,the hexagonal artificial reef.Firstly,a physical model test is used to measure the flow field of the hexagonal artificial reef under two placement methods and various incoming velocities based on particle image velocimetry(PIV);secondly,a numerical model is established using the computational fluid dynamics software FLUENT to investigate the effects of the relative scale,relative incoming velocity and angle of the deflector on the flow field effect of the hexagonal artificial reef by expanding the group.And the flow field effects were compared with those of existing typical artificial reefs.The results of the study show that:Compared with existing typical artificial reefs,the flow pattern inside the hexagonal artificial reef is simple,and there is no large-scale eddy formation in front and behind the reef,which is suitable for constructing a soft flow field;its flow field effect is less affected by the incoming flow velocity and direction,and has good directional adaptability;the maximum upward flow velocity varies from 20% to 40% of the incoming flow velocity when the head-on angle varies from 0° to 30°;the range of the slow flow area is roughly The best geometric parameters for the effect of the flow field in the hexagonal artificial reef are: the external aperture ratio varies from 0.50 to 0.64,with the best aperture ratio being 0.58;the angle of the deflector varies from 21.8° to 33.2°,with the best angle being set at 30.9°.