圆形重力式网箱流场效应的试验研究

为探索圆形重力式网箱在动态流场中的水动力学特性,同时获得网箱系统内部与周围流场分布及流速变化规律,设计了4种不同网目形状和不同网目大小的网箱模型(C1、C2、C3、C4),选取4种不同水流流速(0.068 m/s、0.105 m/s、0.143 m/s、0.182 m/s),分别采用声学多普勒流速仪(ADV)和粒子图像测速(PⅣ)技术对网箱系统内外的流速及流场变化进行测定。结果表明,ADV试验与PⅣ技术测量结果基本一致;来流速度不同时,单个网箱范围内的水流衰减程度差异不大;来流速度相同时,小网目网箱的减流效果优于大网目网箱;网目大小相同时,菱形网目网箱减流效果优于方形网目网箱;群组网箱减流效果明显,且随着水流通过网箱数目的增加,网箱内与网箱后的流速降低明显,其中第2个网箱中心的流速衰减率已经达到了67.6%,第4个网箱中心的流速衰减率为88.2%,网箱后的流速衰减率为72.1%。研究结果可为养殖生产实践中网箱类型的选择提供理论参考。

Experimental study on flow-field effect of circular gravity cage

In order to understand hydrodynamic characteristics of circular gravity cage in varied flow-field, and obtain both the flow-velocity variations and flow-field distribution inside and around cages, four models(C1,C2,C3,C4) were designed to be measured at specific measurement points at a velocity of 0.068m/s,0.105m/s,0.143m/s,0.182m/s by particle image velocimetry (PIV) technique and acoustic Doppler velocimeter(ADV).The experimental data showed that the measurement result of ADV was basically same with that of PIV. The ratio of flow-velocity reduction inside a cage remained approximately the same in different current. On the effect of the flow-velocity reduction ,the cages with small mesh did better than the cages with big mesh and the cage with diamond mesh did better than the cage with round mesh at the same velocity. As current flowed through multiple cages, the flow velocity was gradually reduced. The flow velocity inside and downstream from the cages decreased with increasing number of net cages. The flow-velocity reduction was 67.6% inside the second cage, 88.2% inside the forth cage,72.1%downstream from multiple cages. This research can provide a reference to a suitable type of net cages used in production practice.