基于IBM法的低雷诺数下涡激振动高质量比效应的研究

由深圳市赛格广场大厦在低速风场作用下的强烈有感振动事件可知,高质量比系统的振动问题仍较突出。为澄清涡激振动中的高质量比效应,该文采用一种锐利界面浸入边界法,通过C++编程计算了低雷诺数(Re=80~150)流场中,不同高质量比(m*=14.8~280)、阻尼比(ζ=0.0012~0.036)和质量-阻尼比组合m*ζ对涡激振动的影响。结果表明:通过与文献和实验结果的对比,验证了该方法的准确性和有效性;在高质量比情况下,Re<100时,结构发生"弱锁定"现象,Re=100~130时,发生传统的"锁定"现象,且发生共振时Re=110,位于锁定区间靠近Re数较小的一侧,当Re=130时,开始摆脱锁定,且升力与振动响应出现"相位突变"现象;m*、ζ对锁定区间的影响并不大,但是质量-阻尼比组合m*ζ相同时,质量比对涡激振动的影响更加显著,即质量比低的结构系统发生涡激振动时的锁定区间更广(Re=90~140),m*=14.8的高质量比系统比m*=148的较高质量比系统提高了1.67倍,而且共振时对应的雷诺数也减小;发生共振时,尾涡脱落均为"2S"模态,最大振幅均为0.5D左右,无太大变化,即高质量比和较高质量比对振幅和锁定区间的影响并不大,但是随着ζ的增加,振幅比Y逐渐减小,振动受到了抑制。

EFFECTS OF HIGH MASS AND DAMPING RATIO ON VIV OF A CIRCULAR CYLINDER WITH LOW REYNOLDS NUMBER BASED ON IBM

The vibration problem of the high mass ratio system (the mass of structure is significantly larger than the mass of the surrounding fluid it displaces) is still prominent, as shown by the strong vibration event of Shenzhen SEG Plaza building under the action of low speed wind field. To investigate the high mass ratio effect on the vortex-induced vibration (VIV), the VIV of a circular cylinder supported by lightly damped springs and placed in a uniform flow at Reynolds number 80~150 with high mass ratio (\begin{document}$ {m^*} = 14.8 \sim 280 $\end{document}), damping ratio (\begin{document}$ \zeta = 0.0012 \sim 0.036 $\end{document}) and mass-damping ratio combination (\begin{document}$ {m^*}\zeta $\end{document}) is numerically simulated, and then analyzed using the sharp-interface immersed boundary method (IBM). The results show that: The accuracy and effectiveness of this method are verified through a comparison with literature and experimental results; In most of the high mass ratio cases, the “soft-lock-in” phenomena is observed when Re<100, which is the vortex-shedding frequency not matching the structural frequency exactly, and there is a slight detuning. The “lock-in” phenomena is observed for a range of Re=100~130. The resonance occurs when Re=110, the “lock-in” phenomena begins to disappear to structure when Re>130, and the “phase mutation” phenomenon appears between lift coefficients and cross-flow vibration amplitude; The high mass ratio plays an important role on VIV in the cases with same mass-damping ratio combination (\begin{document}$ {m^*}\zeta $\end{document}). The range of “lock-in” is wider, namely Re=90~140, e.g., the range of the system with mass ratio (\begin{document}$ {m^*} = 14.8 $\end{document}) is 1.67 times wider than the system with higher mass ratio (\begin{document}$ {m^*} = 148 $\end{document}); When resonance occurs, the vortex street mode is “2S” type, and the maximum cross-flow vibration amplitude is 0.5 times of the diameter of cylindrical also. In other words, the mass ratio has little effect on the amplitude. However, with the increase of damping ratio, the amplitude decreases gradually and the vibration is suppressed.