基于PIV技术的方形网箱二维流场分析

Analysis of Two-Dimension Flow Field of the Square Cage Based on Particle Image Velocimetry(PIV)

方形重力式网箱在水流中会产生一定的阻流效应,研究不同类型网箱在不同流速下网箱周围的减流情况非常重要。本研究通过水槽试验,设计了4组不同网目形状与网目尺寸的网箱模型,利用粒子测速技术(PIV)与多普勒流速计(ADV)试验技术,分析方形网箱二维流场特性、流速分布及其减速情况。结果显示,水流经过4组网箱后均出现明显的流速衰减,衰减区的高度与网箱高度大致相当;而网箱底部则出现流速增大区。ADV与PIV测量结果基本一致。当来流速度为0.18 m/s时,4组网箱中心点的平均流速衰减系数在0.5–0.8左右。装配菱形网目的网箱流速衰减略大于方形网目网箱;小网目网箱的流速衰减则明显大于大网目网箱,而网箱的平均流速衰减系数随流速变化趋势不明显。结果表明,利用PIV技术给出经过网箱中心点铅垂面流场分布的云图呈现,可清晰看出网箱周围的水流流线分布疏密程度。

The current in sea can maintain the water quality in the cage, but the strong current can cause serious deformation of the cage and reduce the effective volume of the cage. This study was conducted to research the reduction in flow velocity downstream from square cages in currents. The flow-velocity distribution downstream from cages was invested with four different net mesh shapes and sizes. The reduction in flow velocity was recorded using both the Particle Image Velocimetry （PIV） and Acoustic Doppler Velocimetry （ADV）. The results showed that there was an obvious reduction in flow velocity downstream in the four cage models. The height of the flow-reduction region was approximately the same as the height of the cage. The flow velocity increased at the bottom of the cage. The results achieved by PIV consistent with the data recorded by ADV. The average reduction factor of the four cage models was from 0.5 to 0.8 at 0.18 m/s the incoming velocity. The reduction in flow velocity of the cage with small meshes was greater than the cage with big meshes. The reduction in flow velocity of the cage with diamond meshes was slightly greater than the cage with square meshes. The average reduction factor was not obviously impacted by the incoming velocity. The results of the vertical plane through the center of the cage by PIV were visualized by the velocity nephogram. These findings will contribute to the understanding of the flow characteristics around the square cage.