摘要
为了研究刚性联结对串列双圆柱尾流致涡激振动的减振效果及其流场作用机理,以圆心间距为4D (D为圆柱直径)的无联结及刚性联结串列双圆柱为研究对象,在雷诺数Re = 150时,采用数值模拟方法研究了刚性联结对圆柱振幅、振动轨迹和锁振区域的影响规律,分析了振动响应和气动力之间的内在联系,探讨了两类圆柱振动差异背后的流场机理。研究表明:刚性联结对串列双圆柱的尾流致涡激振动有一定的减振作用,提高了发生涡激振动的起振风速,减小了发生涡激振动的折减速度范围,降低了下游圆柱的振幅,但上游圆柱振幅略有增加。发生尾流致涡激振动时,无联结串列双圆柱和刚性联结串列双圆柱的的流固耦合机制不同,两者的尾流模态有很大差异。
大长细比柱群在实际工程中应用广泛,如大跨度桥梁的并列索、多分裂导线、海洋立管
对于无联结串列双圆柱的流致振动,学者通过试验和数值模拟,探讨了圆柱间距、质量比、雷诺数、振动自由度、阻尼比等参数的影响。Du
以往对刚性联结双圆柱尾流致涡激振动的研究较少。Zha
以往研究表
为了进一步探讨刚性联结对较大质量比双圆柱振动特性的影响规律及其流场机理,本文以圆心间距为4D的无联结及刚性联结串列双圆柱为研究对象,考虑横流向和顺流向两个自由度影响,在雷诺数Re=150,m*=20时,采用数值模拟方法,研究了两类双圆柱发生尾流致涡激振动的动力响应特性和流场特征,探讨了刚性联结对双圆柱尾流激振的减振效果及其流场作用机理。

图1 双圆柱计算模型
Fig.1 Computational model of twin circular cylinders
对于无联结串列双圆柱,其运动方程为:
(1) |
(2) |
(3) |
(4) |
对于刚性联结串列双圆柱,其运动方程为:
(5) |
(6) |
式中 ,和分别为圆柱顺流向的瞬时位移、速度和加速度;,和分别为横流向的瞬时位移、速度和加速度;m为单位展向长度圆柱的质量;ζ为结构的阻尼比;为圆柱的固有圆频率。FD(t) = 0.5ρ
本文通过动网格技术来实现数值模拟中圆柱与流场之间的流固耦合,过程如下:
(1)运用数值模拟方法求解流体控制方程,获得流场速度场、压力场及圆柱表面流体力;
(2)将流体力作用于两自由度振动的圆柱,以四阶Runge‑Kutta法求解圆柱的运动控制方程(式(
(3)通过动网格技术,将振动圆柱的振动速度传递于网格系统,更新网格位置;
(4)返回第(1)步开始计算下一个时间步的响应,如此循环获得各时间步圆柱的动力响应,实现上述流固耦合算法。
双圆柱的计算域及网格划分如图

图2 计算域和边界条件示意图
Fig.2 Schematic drawing of computational domain and boundary conditions

图3 计算域网格方案
Fig.3 Computational domain mesh scheme
边界条件的设置如
本文的计算参数如下:串列双圆柱的圆心间距为4D,雷诺数Re=150,折减速度Vr=U/(fn D)=3~12(U为来流风速,fn为圆柱的自振频率),圆柱的质量比
为保证计算结果的可靠性,首先针对固定单圆柱,研究了周向网格数量、无量纲时间步长和阻塞率等参数对计算结果的影响,并与文献[
进一步针对单圆柱的双自由度涡激振动问题,考虑了三种网格方案对计算结果的影响,网格方案如
计算工况 | 周向网格数量 | Xmean /D | Xrms /D/(×1 | Ymax/D | CD, mean | CD, rms | St |
---|---|---|---|---|---|---|---|
Mesh 1 | 100 | 0.113 | 0.561 | 0.559 | 1.930 | 0.273 | 0.162 |
Mesh 2 | 200 | 0.110 | 0.520 | 0.533 | 1.890 | 0.255 | 0.163 |
Mesh 3 | 400 | 0.110 | 0.516 | 0.531 | 1.880 | 0.252 | 0.163 |
Prasanth, et a | 0.112 | 0.494 | 0.529 | 1.900 | 0.249 | 0.164 | |
He, et a | 0.108 | 0.465 | 0.503 | 1.810 | 0.224 | 0.165 | |
Tu, et a | 200 | 0.131 | 0.566 | 0.525 | 1.880 | 0.266 | 0.165 |

图4 单圆柱和刚性联结双圆柱的涡激振动结果验证
Fig.4 Result verification of the vortex induced vibration of the single circular cylinder and rigidly coupled circular cylinders

图5 串列双圆柱及单圆柱振幅随折减速度的变化
Fig.5 Variation of the amplitude for the double circular cylinders and the single circular cylinder with the reduced velocity
由
当上、下游圆柱之间进行刚性联结后,在Vr = 6时,双圆柱的顺流向振幅达到了0.23D,这与单圆柱和无联结串列双圆柱有很大不同;双圆柱的起振风速Vr = 5,大于单圆柱及无联结上、下游圆柱,在共振范围内双圆柱的振幅约为0.6D~0.8D,略大于单圆柱及无联结上游圆柱。与无联结下游圆柱相比,刚性联结串列双圆柱的振幅极值及出现共振的风速范围均有所减小,说明刚性联结对振动有一定的抑制作用。
以往学者认为,当旋涡脱落频率与固有频率接近时(即fy / fn趋近于1.0),圆柱发生振动锁

图6 横流向振动频率比随折减速度的变化
Fig.6 The vibration frequency ratio as a function of reduced velocity in the transverse direction
值得注意的是,这与Gao
图

图7 平均阻力系数随折减速度的变化
Fig.7 The mean values of the drag coefficients as a function of reduced velocity

图8 脉动气动力系数随折减速度的变化
Fig.8 The r.m.s. values of the aerodynamic coefficients as a function of reduced velocity
由
由
为进一步分析横流向位移与气动升力的关系,

图9 圆柱的横流向振动和升力系数的时程曲线及功率谱图
Fig.9 Time histories and amplitude spectra of oscillation in the transverse direction and lift coefficient of the cylindes
图

图10 无联结串列双圆柱的瞬时能量输入(Vr = 7)
Fig.10 Transient energy input in transverse direction for the uncoupled circular cylinders in tandem arrangement (Vr = 7)

图11 刚性联结串列双圆柱的瞬时能量输入(Vr = 6.5)
Fig.11 Transient energy input in transverse direction for the rigidly coupled circular cylinders in tandem arrangement (Vr = 6.5)
从
从
为了探讨无联结及刚性联结串列双圆柱尾流激振的流固耦合机制,进一步对无联结下游圆柱及刚性联结串列双圆柱在横流向振幅最大时所对应的折减速度下的流场形态进行分析,研究了单个振动周期内上游圆柱脱落的涡与下游圆柱之间的相互作用。

图12 无联结串列双圆柱振幅最大时的涡量图(Vr = 7)
Fig.12 Vortex diagram of two uncoupled tandem circular cylinders at the maximum tranverse amplitude(Vr = 7)

图13 刚性联结串列双圆柱振幅最大时的涡量图(Vr = 6.5)
Fig.13 Votex diagram of two rigidly coupled tandem circular cylinders at the maximum tranverse amplitude (Vr = 6.5)
从尾流模态来看,无联结串列双圆柱的尾流中存在稳定的旋涡脱落,而刚性联结串列双圆柱的尾流则显得较为复杂,两种串列双圆柱的流固耦合机制存在明显差异。
本文在雷诺数Re = 150、圆心间距为4D、质量比m * = 20条件下,对无联结串列双圆柱与刚性联结串列双圆柱尾流致涡激振动的振动响应特性和流场结构进行了数值模拟研究,主要结论如下:
(1)与无联结串列双圆柱相比,刚性联结后下游圆柱的横流向最大振幅减小,而上游圆柱的横流向最大振幅则有所增大,在Vr = 6时还会出现较大的顺流向振动;刚性联结后串列双圆柱的起振风速增大,发生涡激振动的折减速度锁定区范围减小。
(2)刚性联结与无联结串列双圆柱类似,上、下游圆柱的平均及脉动阻力系数均随着折减速度的增加先增大再减小,最后趋于稳定;刚性联结下游圆柱的脉动升力系数大于上游圆柱且随折减速度变化较为剧烈。
(3)两类圆柱的位移与气动升力的关系不同。在横流向最大振幅时,无联结下游圆柱的升力和位移的主频不一致,而刚性联结双圆柱位移和升力的主频均为固有频率。
(4)通过绕流场分析可知,发生尾流致涡激振动时,无联结串列双圆柱和刚性联结串列双圆柱的流固耦合机制不同,且两者的尾流模态具有很大差异。
需要指出的是,本文工作主要是在低雷诺数层流下进行,而实际工程中,结构往往处于高雷诺数湍流环境下。因此,串列双圆柱流致振动的雷诺数效应需要进一步研究。
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