基于大涡模拟与被动示踪物模型的人工鱼礁数值研究

NUMERICAL SIMULATION OF CUBIC ARTIFICIAL REEF UNDER LARGE EDDY IN PASSIVE SCALAR MODEL

投放人工鱼礁是解决海洋生态环境问题的重要措施之一。通过使用并行大涡模拟模式(the parallelizeda large-eddy simulation model,PALM)及被动示踪物模型模块,研究了不同流速条件(0.1,0.2,0.4和0.6 m/s)下方型人工鱼礁对流场形态、营养盐的抬升作用、和湍流动能收支的影响。研究表明,鱼礁的存在使得其附近垂向速度增大,产生上升流。受到上升流的抬升作用,鱼礁底部的示踪物迅速进入海洋上层,之后遇到鱼礁后方的背涡流,示踪物的抬升受阻,高度逐渐降低。在上升流区域以及背涡流区域的共同影响下,示踪物抬升区域的最大高度与来流流速无关。不同上升流定义对应的上升流区域的高度与来流流速均不相关;上升流区域的最大速度、平均速度与来流流速都成线性增加的关系;然而随着来流流速的增大,不同上升流定义对应的上升流区域面积的变化趋势却完全不同。投放鱼礁后,鱼礁区域底部的混合增强,区域底部的能量被输运至上层。这说明,鱼礁的存在不仅对营养物质具有抬升作用,还能将能量向上输运。

Artificial reef is a widely used tool for marine ecosystem improvement.A numerical simulation was conducted in the parallel large eddy simulation model(PALM)in passive scalar mode to explore the effects of solid cubic artificial reef on flow field,turbulent kinetic energy(TKE)budget,and nutrient uplift under four inflow velocities(0.1,0.2,0.4,and 0.6 m/s).Results show that artificial reef significantly increases the vertical velocities near reef,and underpin inflow into upwelling.Scalars at the reef bottom are pushed up to the ocean surface quickly and then sunk by vortex at the reef rear.Under the joint effects of upwelling and vortex,the maximum height of uplift of passive scalar show no relation with inflow velocities.In addition,different definitions of upwelling present no influences on the heights and velocities of upwelling.Both average and maximum velocities of upwelling are increased linearly with inflow velocities.However,the area of upwelling change demonstrates a totally different trend.After reef is placed,mixing at the bottom is strengthened,dissipation and shear are remarkably enlarged,and energy at the bottom is transported to the upper layers.Therefore,artificial reef can not only uplift nutrients,but also transport energy upward.