不同工作姿态下立式双曲面网板水动力及周围流场特性研究

网板是单拖网中实现网具扩张的重要属具,其稳定状态直接决定拖网网口扩张程度,进而影响渔获效率和经济效益。该研究以立式双曲面网板为研究对象,利用水槽模型试验和数值模拟(Computational fluid dynamics,CFD)探究立式双曲面网板在不同倾斜状态(内、外倾斜,前、后倾斜)和冲角下的水动力性能变化,并对网板周围流场和表面压力进行可视化。结果显示:1)模型试验和数值模拟的网板升力系数均在倾角为0°,冲角为25°时达到最大值,分别为1.69和1.88;而两者的阻力系数均随倾角增大逐渐减小。2)模型试验和数值模拟的升阻比均随倾角增大逐渐减小;当内倾角为5°时,两者的升阻比均达到最大,分别为3.27和3.69。3)压力中心系数Cpb随倾角变化基本保持不变;但当网板处于前倾状态时,Cpc随倾角增大而增加;而网板处于后倾状态时,Cpc随倾角增大逐渐减小。4)CFD结果显示,网板中心面后部旋涡随倾角增大逐渐减小;当网板处于内、外倾状态时,前端流速衰减区随倾角增大逐渐增加;但当网板处于前、后倾状态时,衰减区随倾角增大逐渐减小;网板处于前倾状态时,压力中心随倾角增大逐渐向网板上端翼弦移动,网板处于后倾状态时则出现相反结果。研究结果可为今后研究网板稳定性和合理使用及调整网板提供科学参考。

Hydrodynamic performance and around flow field of biplane-type otter board with different working positions

Otter board,an important accessory for net expansion in the single trawl,whose stability directly determines the degree of expansion of the trawl mouth and affects the catch efficiency and economic benefits.In this study,the hydrodynamic performance of the biplane-type was investigated by using the flume tank experiment and numerical simulation(Computational fluid dynamics,CFD)at different heel angles(inward,outward and tilt)and angles of attack,and the flow field and surface pressure around otter board was visualized.The results show:1)At heel angle of 0°and angle of attack of 25°,both the lift coefficients of otter board for flume tank experiment and numerical simulation reached the maximum values(1.69 and 1.88,respectively),while both drag coefficients decreased with increasing heel angle.2)Both the lift-to-drag ratios of model experiment and numerical simulation decreased with the increase of heel angle,and both reached the maximum values(3.27 and 3.69,respectively)when the heel inward angle was 5°.3)The pressure center coefficient(Cpb)almost maintained stable with the change of heel angle;Cpc increased and decreased with increasing heel angle when the otter board was set to forward and backward tilting states,respectively.4)CFD results show that the vortex at the rear of the center surface of otter board decreased with increasing heel angle.When the otter board was in inward and outward inclination states,the front end flow velocity reduction zone increased with increasing heel angle gradually.The pressure center moved toward the end chord of otter board as the heel angle increased in forward tilting state,but moved toward the lower end chord in backward tilting state.The results can provide scientific references for the studies on the stability of otter board and adjustion of fishing strategy.