不同迎流攻角下正多边形柱流致振动特性

Numerical simulations of flow-induced vibrations of polygonal prism with different angles of attack

采用嵌入式迭代浸入边界法对不同迎流攻角下边数3≤N≤7的正多边形柱流致振动进行了二维数值模拟,基于多边形有效长度的雷诺数为Re=100,质量比为m*=m/mf=5(m为柱体的质量,mf为柱体排开水的质量),折合流速为1≤Ur=U/f_(n)D_(e)≤20(U为入流流速,f_(n)为柱体的自振频率,D_(e)为柱体迎流有效长度)。研究了边数对正多边形柱体振动响应的影响,分析了横流向振幅、平衡位置偏移、水动力系数和振动频率随边数、迎流攻角和折合流速变化的情况。结果表明,随着边数的增加,正多边形柱体的振动特性趋于圆柱。当边数N=7时,不同折合流速下,正多边形柱体的振幅、升阻力和频率等都与圆柱的基本相同。三角柱在迎流攻角0°≤α≤15°时,振动响应为涡振-驰振联合模式;α=20°时,为涡振-驰振分离模式;22.5°≤α≤60°时,为涡振模式。其他棱柱的振动响应在不同迎流攻角下均表现为涡振模式。

In this paper,the flow induced vibration of a regular polygonal prism with a side number of 3≤N≤7 and different angles of attack is studied by using the immersed boundary method.The Reynolds number based on the effective length of the polygonal prism is Re=100,the mass ratio is m*=m/mf=5(where m and mf are the prism and displaced fluid mass,respectively),and the reduced velocity is 1≤Ur=U/f_(n)D_(e)≤20(where U is the incoming flow velocity,f_(n)is the natural frequency of the prism and D_(e)is the incoming flow effective length of the prism).The influence of the edge number of the regular polygonal prism on the vibration responses is studied.The transverse vibration amplitude,the lateral shift of the balanced position,the hydrodynamic coefficients and the vibration frequency are investigated with different edge numbers,angles of attack and reduced velocities.Results show that the vibration characteristics of the polygonal prism approach that of a circular cylinder with the increasing number of edge.When the edge number N=7,the vibration amplitude,the lift and drag coefficients and the vibration frequency of the polygonal prism are almost the same as those of a circular cylinder at different reduced velocities.For the triangular prism,the vibration mode is the combined vortex-induced vibration(VIV)and galloping in the range of angle of attack 0°≤α≤15°,separated VIV and galloping atα=20°,and VIV in the range of 22.5°≤α≤60°.However,other polygonal prism exhibit VIV responses at all angles of attack.