鱼类自主游动推进机理与游动性能二维数值模拟研究

Numerical simulation of propulsion mechanism and swimming performance of 2D fish autonomous swimming

推进机理及游动性能研究对鱼类洄游通道建设具有重要意义。利用计算流体动力学方法结合重叠网格技术,通过编译控制鱼体摆动的UDF程序,对二维鱼类自主游动进行模拟,分析鱼体压力场分布及反卡门涡街结构演化过程与参数变化情况,开展不同摆尾频率、摆尾幅度、鱼体体形及尾鳍尺寸等参数下鱼类游动性能及鱼体受力的变化情况,揭示鱼类自主游动过程中的游动机理。研究结果表明:(1)鱼体尾鳍周期性往复摆动下漩涡脱落形成反卡门涡街,是鱼体前进推力的主要来源,且随着摆尾频率、摆尾幅度的增加,鱼体尾部涡街长度、涡街强度逐渐增加,而摆尾幅度对涡街宽度的影响较大;(2)随着摆尾频率、摆尾幅度的增加,纵向平均合力系数和最大侧向力系数均增大,使得鱼类获得较大的游动速度,但摆尾频率改变时平均合力系数和游动速度的增加更为明显,摆尾幅度改变时最大侧向力系数的增加更为明显;(3)随着体宽指数的增加,纵向平均合力系数逐渐减小,需克服的游动阻力增加,使得鱼类游动速度逐渐减小,而最大侧向力系数逐渐增加;(4)随着尾鳍指数的增加,纵向平均合力系数和最大侧向力系数均增大,使得鱼类游动速度逐渐增大。研究成果可为鱼类生境恢复营造提供支撑。

The propulsion mechanism and swimming performance are of great significance to the construction of fish migratory channels.By using computational fluid dynamics method combined with overlapping mesh technology,the two-dimensional fish autonomous swimming was simulated by compiling the UDF program for controlling fish body swing,analyzing the evolution process and parameter changes of fish body pressure field distribution and inverse Carmen vortex street structure,carrying out the changes of fish swimming performance and fish body force under different parameters of tail swing frequency,tail swing amplitude,fish body shape and tail fin size,etc.,and revealing the swimming mechanism of fish in the process of autonomous swimming.The results show that:(1)the fish body’s tail fin periodically swings back and forth under the formation of anti-Carmen vortex street,which is the main source of the fish body forward thrust,and with the increase of tail swing frequency and tail swing amplitude,the fish body tail vortex street length and vortex street strength gradually increase,while the effect of tail swing amplitude on the vortex street width is greater;(2)with the increase of swinging frequency and swinging amplitude,the horizontal mean coefficient of synergy and the maximum lateral force coefficient increase,which makes the fish obtain a larger swimming speed,but the increase of mean coefficient of synergy and swimming speed is more obvious when the swinging frequency has been changed,and the increase of maximum lateral force coefficient is more obvious when the swinging amplitude has changed;(3)with the increase of body width index,the horizontal average coefficient of force gradually decreases,and the swimming resistance to be overcome increases,which makes the swimming speed of fish gradually decrease,while the maximum lateral force coefficient gradually increases;(4)and with the increase of caudal fin index,both horizontal mean coefficient of force and maximum lateral force coefficient increase,which leads to the gradual increase of swimming speed of fish.The results of the study can provide a support for fish habitat restoration.