沉降对多孔方型人工鱼礁流场效应影响的数值模拟

Numerical simulation of effect of settlement on flow field of porous square artificial reef

摘要:

礁体沉降作为人工鱼礁投放后普遍产生的现象,对人工鱼礁周围流场会产生影响。为研究多孔方型人工鱼礁不同沉降情况下流场效应的变化,采用计算流体动力学(Computational fluid dynamics,CFD)技术,利用Fluent软件模拟在固定来流流速为0.8 m/s时,5种不同沉降程度下单体鱼礁周围的流场情况。结果显示:与无沉降时(初始状态)相比,在沉降程度为20%时,上升流最大高度降低约1.0 m,最大上升流流速增大约0.015 m/s,侧向流速增大区域(大于来流速度)扩大至1.5倍左右,同时礁体背流面透水区域增大,背涡流区域沿水流方向移动约2 m,礁体周围流场情况一定程度上变得更加复杂;在沉降程度为40%时,上升流流速最大值与初始状态相比减少约为0.010 m/s,侧向流增大区域基本一致,此时礁体背流面透水区变化较大,有形成一个逆时针涡旋的趋势;当沉降程度达到60%时,礁体周围流场效应开始明显下降,上升流最大高度相较于初始状态降低约3.2 m,上升流最大流速降低约0.600 m/s,侧向流速增大区域与壁面间距缩短约0.4 m,背涡流区域有消失的迹象;在沉降程度达到80%时,礁体流场效应基本丧失。研究表明,对于多孔方型人工鱼礁,在沉降程度40%以内,人工鱼礁仍然能够发挥着较好的流场效应;礁体在沉降程度达到60%时,礁体周围流场复杂程度相较于初始状态有明显损失,之后随着沉降深度增加,礁体流场效应逐渐消失。

Abstract:

As a common phenomenon after artificial reefs are put into operation, reef settlement will have an impact on the flow field around artificial reefs.In order to study the change of flow field effect under different settlement of porous square artificial reef, the flow field around single reef to five different settlement degrees was simulated by using computational fluid dynamics (CFD) technology and Fluent software when the fixed incoming flow velocity was 0.8 m/s.The results showed that compared with the case without settlement (initial state), when the settlement degree was 20%, the maximum height of upwelling decreased by about 1m, the maximum upwelling velocity increased by about 0.015 m/s, the lateral velocity increase area (greater than the incoming velocity) expands to about 1.5 times, at the same time, the permeable area of the reef back flow surface increased, and the back vortex area moved about 2 m along the flow direction. The flow field around the reef becomes more complex to some extent;When the settlement degree is 40%, the maximum value of upwelling velocity decreases by about 0.01 m/s compared with the initial state, and the increasing area of lateral flow is basically the same. At this time, the permeable area of reef back flow surface changes greatly, and there is a trend of counterclockwise vortex; When the settlement reaches 60%, the flow field effect around the reef begins to decrease significantly, the maximum height of the upwelling decreases by about 3.2 m compared with the initial state, the maximum velocity of the upwelling decreases by about 0.6 m/s, the distance between the lateral velocity increasing area and the wall shortens by about 0.4 m, and the back vortex area seemed disappear;When the settlement reaches 80%, the flow field effect of reef body basically lost.The results showed that for the porous square artificial reef, the artificial reef can still play a good flow field effect when the settlement degree is less than 40%; When the settlement of the reef reaches 60%, the complexity of the flow field around the reef is obviously lost compared with the initial state. Then, with the increase of the settlement depth, the flow field effect of the reef gradually disappears.