FLUIDELELASTIC INSTABILITY, VORTEX-INDUCED VIBRATION AND SYMMETRY BREAKING IN HELICAL ARRAYS OF CYLINDERS SUBJECTED TO CROSS-FLOW

本研究计划探讨由高度空间对称性的多组分组成的大型系统中的流固耦合问题。所考虑的物理系统是一组受平行于螺旋轴的外部流影响的螺旋管。螺旋几何管阵列是紧凑的热交换器设计的理想选择。与直管或u形管换热器相比，螺旋管换热器在单位体积的空间内具有更大的传热表面积。最近的技术发展和对小型能源发电系统（例如小型模块化核反应堆，热太阳能发电系统）的关注正在推动人们对螺旋几何热交换器中的流固相互作用重新产生兴趣。除了工业应用外，螺旋管阵列中高度复杂的流动也为流固耦合领域提出了一些具有挑战性的基础研究问题。螺旋管的强自耦合会由于沿螺旋方向的强流固相关而导致不稳定性增强。由于沿螺旋方向的涡脱落同步引起的强涡激振动也是一个重要的问题。本研究的主要目的是研究螺旋几何结构在平行于螺旋轴的气流作用下的流固耦合动力学。预期的主要流动激励现象是涡激振动和流体弹性不稳定。虽然这些现象对于直管阵列已经很好地理解了，但螺旋管的几何形状以一种非平凡的方式改变了FSI问题。提出的研究计划将解决几个相关的流体-结构相互作用（FSI）问题。首先是螺旋管阵列几何中的流体弹性不稳定性问题。将进行实验测试和理论模型开发。第二个FSI问题涉及涡性脱落和涡性诱发振动（VIV）。这个问题将使用计算流体动力学（CFD）和实验方法来解决。使用PIV技术的实验流动可视化也将在螺旋管阵列中进行。该研究计划旨在解决螺旋几何管阵列中流激振动的基本机制。这些阵列是高度紧凑的螺旋几何热交换器和蒸汽发生器的关键部件。提出的研究计划有望为这些工业部件稳定性分析的新方法的发展做出贡献。

The proposed research program investigates the problem of fluid-structure interaction in large systems consisting of multiple components interconnected with high spatial symmetry. The physical system under consideration is an array of helical tubes subject to external flow parallel to the helix axis. Helical geometry tube arrays are ideal for compact heat-exchanger design. Compared to straight or U-bend tube heat exchangers, helical tube heat exchangers have a much larger heat transfer surface per unit volume of space occupied by the heat exchanger. The recent technological developments and focus on small-scale energy generation systems (e.g. small modular nuclear reactors, thermal solar power systems) is driving renewed interest in fluid-structure interaction in helical geometry heat exchangers. In addition to industrial applications, the highly complex flows in helical tube arrays presents some challenging fundamental research problems in the area fluid-structure interaction. The strong auto-coupling of the helical tubes can lead to enhanced instability due to strong fluid-structure correlation along the helix. Strong vortex-induced vibration due to vortex shedding synchronization along the helix is also expected to be an important problem. The primary objective of the proposed research is to investigate the fluid-structure interaction dynamics of helical geometry structures subjected to flow parallel to the helix axis. The primary flow-excitation phenomena expected are vortex-induced vibration and fluidelastic instability. While these phenomena are fairly well understood for arrays of straight tubes the helical tube geometry changes the FSI problem in a non-trivial manner. The proposed research program will address several related fluid-structure interaction (FSI) problems. The first is the problem of fluidelastic instability in helical tube array geometries. Experimental testing and theoretical model development will be done.  The second  FSI problem relates to vorticity shedding and Vorticity Induced Vibrations (VIV). This problem will be addressed using computational fluid dynamics  (CFD) and experimental methods. Experimental flow visualization using PIV techniques will also be performed in the helical tube array.  The research program aims to address the fundamental mechanisms underlying flow-induced vibrations in helical geometry tube arrays. These arrays are the key component of highly compact helical geometry heat exchangers and steam generators. The proposed research program is expected to contribute to the development of new methods for the stability analysis of these industrial components.