被动控制圆柱涡振-驰振过渡区振动特性及激励机理

Vibration characters and driving mechanism of a circular cylinder with passive turbulence control during the transition from VIV to galloping

为了研究处于涡致振动(VIV)上部分支-驰振过渡区域的被动湍流控制单圆柱的流致振动特性,采用有限体积法,选取Spalart-Allmaaras湍流模型,通过求解二维非稳态雷诺平均Navier-Stokes方程进行数值计算。仅考虑柱体在模流方向上的振动,分析了柱体的振幅、频率、升力和尾涡形态,并揭示了驰振的激励机制。本文数值计算结果与实验数据吻合良好。结果表明,柱体处于VIV上部分支-驰振过渡区域时,随着折减速度增加,柱体的振幅持续上升,振动频率则缓慢下降,逐步过渡到高振幅、低频率的驰振阶段。柱体发生驰振后,最大振幅比达到了3.88D。随着柱体从VIV上部分支向驰振过渡,柱体的升力始终与位移保持同相(相位差为0°),升力始终能促进柱体振动。同时,由于被动控制圆柱表面的粗糙带改变了圆柱壁面附近的流场特性,造成圆柱上下侧的分离剪切层被拉伸到接近垂直于来流方向的位置,在圆柱上下两侧形成较大的压差,形成新的激励机制进而引发驰振。

In this work,flow-induced motions(FIMs)of an elastically mounted circular cylinder with roughness strips in the transition between Vortex-induced Vibrations(VIV)upper branch and galloping are investigated by solving the 2-D URANS equations in combination with the Spalart-Allmaras turbulence model with a finite-volume discretization method.The vibration of the PTC-cylinder is constrained to the transverse direction only.The vibration amplitudes,vibration frequencies,lift coefficients and the vortex structures are discussed,and the driving mechanism is also revealed.The numerical results correspond well with the experimental data.The results show that during the transition from VIV upper branch to galloping,the amplitudes of the cylinder increase continuously with the increasing reduced velocity,while the vibration frequency gradually decreases,and gradually transitions to the high amplitude,low frequency galloping stage.After the cylinder gallops,the maximum amplitude ratio reaches 3.88D.The phase differences between lift force and displacement are all close to 0°in the transition from VIV upper branch to galloping,and the lift force can promote the vibration to galloping efficiently.Meanwhile,the increase of shedding vortices,the differentiation of vortex intensity and the complication of the vortex pattern intensify the pressure fluctuation on the surface of the cylinder,which can intensify the fluid-structure interactions.