Numerical Simulation Of Flow Field Effect Around The Cross-wing Series Artificial Reef

Due to overfishing and intensified environmental pollution in the coastal waters,China 's offshore fishery resources have suffered a serious decline,and marine pasture construction has received much attention.Marine pasture is a new type of sustainable marine fisheries proliferation method that meets the needs of China's fishery industry,and plays an important role in the proliferation and protection of fishery resources.Artificial reef as the basic structure of marine pasture construction,are extremely important for their hydrodynamic research.The hydrodynamic characteristics of artificial reef mainly focus on their flow field effects and stability.The artificial reef' flow field effect is the basis for realizing its principle of proliferation and aggregation.After the artificial reef is placed on the ocean floor,it forms upwelling and wake vortex,which promotes the circulation of nutrients in the upper and lower water layers.The shape of the artificial fish reef single structure has a great influence on its flow field effect.It is of great significance to study the reef flow field effects of different structures on the optimization design and configuration of artificial reefs.In this paper,Fluent with the large eddy simulation(LES)turbulence module is used to numerically simulate the flow field effects of four double-layer cross-wing artificial reefs,three reef double-layer octagonal artificial reefs derived from three crosswing reef,with different upstream angles.Through the analysis of the flow field data,the specific volume method is used to obtain the relative parameters of upwelling and wake vortex,the average velocity of upwelling and wake vortex,and the optimal reef structure of the two reef types.Then,the two reef types are compared and analyzed to study the optimal reef type design.The results show that:(1)The roof structure has no gain on the flow pattern effect of the double-layer cross-wing artificial reef.The volume and relative volume of the upwelling and wake vortex flow of the AB-type sub-reef with the roof are smaller than the AA-type reef without roof,and the utilization rate is reduced,The economy becomes worse;(2)The side plate structure has a significant gain on the flow pattern benefits of the double-layer cross-wing artificial reef.With the increase of the side plates,the relative volume of the ascending flow becomes larger,the relative volume of the wake vortex also gradually increases,and the average velocity of the wake vortex gradually decreases.In short,the increase of the side plate can form a better flow field effect.Double-layer cross-wing type reef design should consider adding side panel structure;(3)The change of the heading angle has five significant differences in the volume of the upwelling and wake vortex of the four double-layer cross-wing reef,and the AD reef has a good adaptability to the tidal current in natural seas;(4)Among the four kind of reefs of the double-layer cross-wing artificial reef,the upwelling and wake vortex effects of the AD reef are the best.The transport is also the largest,the average velocity of the back vortex is the smallest,and the effect of upwelling and wake vortex is the best.It is currently the best structural design of the double-layer cross-wing reef;(5)the artificial fish reef transport flux index to the upper water body,combined with the nutrient concentration difference of the surface and bottom water bodies of the on-site sea area,can effectively quantitatively calculate the salt flux of the artificial fish reef to the upper water body;(6)The roof structure has little effect on the flow field benefit of the doublelayer octagonal artificial reef.The relative volume of the upwelling and wake vortex of the BB reef with roof is lower than that of the BA reef,and the flow velocity of the back vortex is not reduced.The increase of the roof makes the utilization of the reef worse,which increases the amount of concrete.Considering the economic benefits,reefs with roofs have lower benefits than reefs without roofs;(7)The side plate structure has a positive effect on increasing the flow field effect of the double-layer octagonal artificial reef.After the side plate is added,the volume and relative volume of the upwelling are significantly increased,which can form the best upwelling benefit.The wake vortex volume and relative volume are also increased,and the wake vortex flow rate is reduced,and the wake vortex effect is better.In short,The increase of the side plate structure has an effect on improving the flow field effect of the double-layer octagonal artificial reef;(8)The double-layer octagonal artificial reef has a better fluidity benefit than the doublelayer cross-wing artificial reef.The relative volume of the upwelling and the wake vortex of the BC type reef is larger than that of the AC type reef.The relative volume of the ascending current and the wake vortex of the sub-reef are larger than that of the AD-type sub-reef,and the double-sided octagonal reef body has a larger volume of empty space and a smaller volume of concrete.From the comprehensive consideration of economics and flow benefits,the double-layer Eight prism-shaped artificial reefs can form better benefits;(9)The upwelling volume of AD type,CD type and BD type reef is similar to the relative volume,the height of CD type upwelling is the highest,the BD type has the largest upward transport capacity,the volume and relative volume of wake vortex are the best,and the benefit of wake vortex is the best.On the same economic basis,if you need a greater upwelling effect,you can choose the CD-type reef,to get a strong upward water transport capacity and wake vortex effect,you can choose the BC-type reef.In short,the design of the cross-wing series artificial reefs should consider adding side plate structures,and the reef frame can use double-layer octagonal reefs.