多分裂导线流场子结构之间的非线性相互作用

Flow interferences inbetween bundled conductors are not only the essential reason for its drag variations but also the origin for the vortex exciting forces of every sub-conductor. Due to the complexity of flow interfering mechanism as well as the interfering intensity governed by multiple parameters (conductor configuration, free-stream flow speed, etc.), the designing standards are not capable of providing a favorable way for accurate prediction of bundled-conductor drags. To have a thorough insight into the flow interferences inbetween bundled conductors, mechanism studies will be carried out based on circular cylinder groups both experimentally and numerically: a) detection and classification of flow substructures in the cross flow around circular cylinders; b) simultaneous measurement of transient flow parameters as well as unsteady aerodynamic forces of circular cylinders. By refering to the time points corresponding to the peak as well as trough values of aerodynamic forces, transient flow patterns will be extracted, and the ones determining the unsteady aerodynamic forces will be presented; c) parametric studies will be conducted to investigate both group parameters( including circular cylinder configurations, distance inbetween cylinders) and free-stream flow parameters(including Reynolds number, turbulence intensity and incidence angle of circular cylinders) onto the spacial length scales as well as the evoluting time scales. Based on the researches conducted above, the flow interference mechanisms will be unveiled, and the influence of group parameters as well as free-stream flow parameters onto unsteady aerodynamic forces will be determined. This could be a mechanism reference for unsteady flow interference as well as a technical reference for exciting forces for bundled conductors.

多分裂导线之间的流动干扰不仅是影响其体型系数的主要原因，同时还对子导线的涡激励力有明显影响。由于流动干扰机理的复杂性以及流动干扰强度受到导线布局、来流速度等多个因素的影响，当前设计规范均不能准确评估多分裂导线的体型系数。为深入揭示多分裂导线之间的流动干扰机理，本项目将基于简化的圆柱群模型，从试验和数值模拟两方面着手开展研究工作：a）对圆柱群流场的子结构进行分类研究；b)同步测量圆柱群的三维瞬态流场与各个圆柱瞬态气动力，并基于瞬态气动力特征状态对应的瞬态流型，统计得到对气动力脉动特性起决定性作用的瞬态流型；c)研究群落参数（包括圆柱布局和圆柱间距）和不同来流参数（包括雷诺数、湍流度和迎角）对流场子结构的长度尺度和演化时间尺度的影响。通过上述工作，最终得到圆柱群的流动干扰机理以及群落参数和来流参数对非定常气动力特性的影响机理，从而为多分裂导线提供流动干扰机理的理论指导及风荷载特性参考。

针对多分裂导线之间的流动干扰问题，基于公开发表文献和专著，研究了影响圆柱及圆柱群流动的参数，指出了几何参数（如直径、长细比、自由端、堵塞度等）、来流参数（如湍流度、来流平均速度）等对流动的关键作用。并选择关键因素中的来流参数及绕流形成的流动特征（无粘流流场和湍流流场）作为给定布局的圆柱群流动干扰的流场子结构开展研究工作。通过求解不同湍流模型封闭的Navier-Stokes方程得到了光滑圆柱的体型系数、斯特劳哈尔数，并与试验结果对比，检验并选择了适合的湍流模型及相关数值算法。采用数值模拟方法研究了不同布局圆柱群的流动干扰特性并分析了流场子结构之间的影响，认为四圆柱流场子结构之间的流动干扰可以分为：.1）近距干扰（D=2d~4d）。流场子结构之间的干扰持续存在，并且主要是无粘流场子结构（尾迹中的无粘速度）、尾迹外的无粘流振荡对下游的影响，粘性的湍流流场子结构之间的相互影响，以及下游几何布局对上游的影响。 .2）中距干扰(D=6d~8d)。流场子结构之间的流动干扰特性直接取决于风攻角的变化。在0°和45°风攻角条件下，上游圆柱对下游圆柱的流动干扰主要是无粘流场子结构，而粘性流场子结构如湍动能和湍流耗散率则在气流向下游流动的过程中明显耗散；在5°和40°风攻角条件下，上游圆柱的尾迹部分撞击在下游圆柱上，无粘流场子结构之间有明显的流动干扰；在10°~35°风攻角条件下，上游尾迹两侧的无粘振荡流动对下游圆柱的绕流及尾迹流动有明显干扰作用。.3）远距干扰(D=10d~20d)。上游圆柱尾迹中的湍流流场子结构的能量耗散显著，对下游圆柱的影响较弱。但其无粘流场子结构对下游圆柱的影响与中距干扰的类似，都受到风攻角的显著影响。.六圆柱的流动干扰行为非常复杂，主要是至少两根甚至多根圆柱之间产生相互作用。.总之，间距、风攻角显著影响了流场子结构的特性及演变性态，对整个圆柱群的流动性态起到了关键作用。