【作者】 王鹏；

【导师】 周裕；

【作者基本信息】 哈尔滨工业大学 ， 流体机械及工程， 2022， 博士

【摘要】 随着传统化石能源的日趋枯竭,以及燃烧化石燃料给人类生存环境带来的负面影响日益凸显,核电作为一种高效、清洁、安全和经济的能源受到越来越广泛的关注。随着先进核反应堆技术的快速发展,如何能保证核反应堆的安全稳定运行就显得尤为重要。燃料棒和控制棒剧烈流致振动是引起燃料棒磨损、疲劳甚至核泄漏的主要原因。因此柱体结构轴向流致振动的研究对于大功率小型化核反应堆技术的发展具有较高的工程应用价值,同时对于相关流固耦合问题的研究具有重要的理论意义。目前国内外关于弹性柱体轴向流致振动的实验研究和理论成果较匮乏,对柱体振动和湍流流场之间的流固耦合作用机理的理解还有待深入。本工作旨在通过对圆柱体束内复杂湍流结构和弹性柱体振动特征进行系统测量,从而深入研究弹性柱体流固耦合的内在物理机理。本实验中弹性柱体模型是由硅橡胶（RTV-4230-E）制作而成,刚性柱体则是采用FEP（氟化乙烯丙烯聚合物）管,其折射率（1.338）和水的折射率（1.333）相接近。实验中水洞来流流速的变化范围0.20-2.12 m/s,其对应湍流度约为0.71%-0.80%。柱体间隙^*（=/,其中为柱体中心距离,为柱体直径）的变化范围为1.21-1.71。同时将湍流发生器固定在实验测试段上游从而产生稳定并且各向同性的高湍流度流场（2.30%-2.91%）。本课题通过多普勒测振仪和粒子图像测速仪对弹性柱体振动和湍流流场进行同步测量,并对弹性柱体振动特性和周围流场特征参数进行详细分析。来流流速和湍流度对弹性柱体轴向流致振动有着显著的影响。随着流速的增加,弹性柱体壁面大涡量结构破碎成小涡量结构并远离壁面,弹性柱体剪切层不稳定性增强,从而引起弹性柱体大幅度振动。在相同流速下,随着来流湍流度的增大,来流湍流结构和弹性柱体剪切层的相互作用增强柱体剪切层不稳定性,造成弹性柱体壁面速度脉动和压力脉动增大,进而引起弹性柱体剧烈振动,但是弹性柱体主振动频率保持不变。对于一根弹性和两根刚性并列分布的圆柱体束,实验发现随着间隙比的降低,根据柱体振动和流场特性可以划分成两个区域。在区域I（^*≥1.57）内,间隙比的减小导致柱体间隙内流速降低,抑制柱体壁面剪切层不稳定性,从而引起弹性柱体振动幅值的降低。在区域II（^*<1.57）内,柱体壁面涡量结构分离并与对侧壁面涡量结构发生相互作用,激发了弹性柱体剪切层不稳定性,使得弹性柱体大幅度振动;在无刚性柱体一侧,壁面涡量结构的破碎和分离造成柱体不稳定剪切层增厚,同时高动量流体流进壁面,增强柱体近壁面流体动量交换,弹性柱体从流场获得足够的能量而剧烈振动。对于一根弹性和多根刚性圆柱体束,在低湍流度（0.71%-0.80%）时刚性柱体数量的增加或柱体间隙值的降低会在圆柱体束内产生较高速度梯度,造成弹性柱体壁面涡量结构的分离,并与对侧柱体壁面涡量结构相互作用,增强弹性柱体剪切层的不稳定性而使得弹性柱体剧烈振动。当来流湍流度提高到2.30%-2.91%,柱体间隙值对弹性柱体振动的影响大幅度减弱,来流湍流脉动在弹性柱体流固耦合作用中占主导作用。来流湍流脉动会激发弹性柱体剪切层的不稳定性,增强弹性柱体壁面涡量结构运动强度,造成弹性柱体振动幅值增大,而间隙比变化引起的梯度效应减弱;同时湍流程度的提高会削弱间隙内流场脉动速度和弹性柱体振动的同步性。综上所述,本课题对于不同来流湍流度下弹性柱体轴向流致振动进行了系统性的实验研究。通过对弹性柱体振动和周围流场的同步测量,揭示了湍流度对弹性柱体振动流固耦合作用的影响。基于不同间隙比下柱体振动响应和流场特征,对并列三根柱体束振动进行了分区,阐明了弹性柱体振动和流场流动结构相互耦合的机理。本文的研究结果进一步加深对轴向流致振动和相关耦合机理的理解,这不仅对核反应堆的设计和安全运行有着重要的指导意义,同时也有利于未来先进核反应堆技术的发展。更多还原

【Abstract】 With the increasing consumption of traditional fossil energy sources and the negative impact of burning fossil fuels on the human environment,nuclear power is receiving more and more attention as an efficient,clean,safe and economical energy source.As the advanced nuclear reactor technology develops rapidly,it is particularly important to ensure the stable operation of nuclear reactors.Axial-flow-induced vibration of fuel rods and control rods is the main cause of fuel rod wear,fatigue and even nuclear leakage.Thus,research on the axial-flow-induced vibration of fuel rods has a high engineering application value for the development of miniaturized nuclear reactor technology,and is also of great theoretical significance for the study of fluid-structure coupling problems associated with a group of cylinderical structures.The systematic experimental studies and theoretical achivements on the axial-flow-induced vibration of elastic cylinder are scare,and the understanding of the mechansim of fluid-structure coupling betweent elastic-cylinder vibration and the surrounding turbulent flow field is still to be improved.The present work aims to provide a systematic exper-imental study on the complex turbulent flow and vibration characteristics of the elastic cylinder in a cylinder cluster,and further gaining a deeper understanding of the physical mechanism of the coulping between the cylinder vibration and flow structures.The elas-tic cylinder in this experiment is made of silicone rubber（RTV-4230-E）,while the rigid cylinder is made of FEP（Fluoro-Ethylene Polymer）tube,whose optical refractive index is close to the water.The range of the incoming flow velocity in water tunnel is 0.20-2.12m/s,which corresponds to a turbulence intensityof 0.71-0.80%.The range of gap width^*（=/,whereandis center to center cylinder gap width and the cylinder diamater,respectively）is 1.21-1.71.The turbulence generator was fixed upstream of the test section to produce a stable and isotropic flow field with a high turbulence intensity（2.30%-2.91%）.In this project,the cylinder vibration and turbulent flow field are measured simultaneously through a Doppler vibrometer and a particle image velocimeter PIV,and a detailed analysics of the vibration characteristics and turbulent flow parameters in the cylinder bundle is conducted.The experimental results show that the free-stream flow velocity and turbulence intensity have a significant effct on the axial flow-induced vibration of the elastic cylinder.As flow velocity increases,the large eddy structures near the elastic cylinder wall break up and separate away from the cylinder wall,enhancing the the shear layer instabilities of the elastic cylinder and exciting the cylinder.At high（2.30%-2.91%）,the high turbulence fluctuations in the incident flow interacts with the shear layer around the cylinder,promoting instabilities in the shear layer around the elastic cylinder.As a result,the wall pressure fluctuations and near-wall fluctuating velocity are amplified,casuing larger vibration amplitude than its counterpart at low（0.71%-0.8%）.However,the dominant vibration frequency remains unaffcted by an increases in.For a tandem cylinder bundle with one elastic-cylinder and two rigid-cylinders,two regimes,i.e.,RI（^*≥1.57）and RII（^*<1.57）are identified based on their distrinct behaviors in the cylinder vibration and flow strcutures.In RI,a drop in^*lead a significantly decrease in the maximum axial flow velocity across the gap between the cylinders,which suppress the flow instability in the shear layer around the elastic cylinder,thus accounting for the contracted vibration amplitude.While in RII,an amout of large eddy structures are observed to separate from the wall,developing towards the center of gap and interacting with the eddy sructures on the opposite cylinder wall,thus resulting into the amplified instabilities of shear layer around the elastic cylinder,which is responsible for the sharp rise in vibration amplitude.While on the other side that not containing rigid cylinders,the broken and separation of near-wall eddy structures contributes to the thickened and more unstable shear layer,while the high momentum fluid flows more easily inward the cylinder wall,thus enhancing the fluid momentum transfer near the cylinder wall.As a result,the elastic cylinder receives sufficient energy from the flow fied to vibrate substantially.In a one-elastic and multiple-rigid cylinder cluster,at low（0.71%-0.80%）,an increase in the rigid cylinder number or a decrease in the gap width would produce a high velocity gradient within the cylinder bundle,causing the eddy structures to separate from the wall and actively interact with the eddy structures near the neighbouring cylinder.As a result,the instability of shear layer around the elastic cylinder is excited,which causes the cylinder to vibrate substantially.Whenincreases to 2.30%-2.91%,the influence of gap width on the elastic-cylinder vibration is weakened,and the incident flow fluctuations plays a key role in the flow-structure interaction of elastic cylinder.The instability of shear layer around the elastic cylinder is amplified by the incident flow fluctuations of a high,enhancing the eddy activities around the elastic cylinder wall,and thus resulting into the large vibrtion amplitude of elastic-cylinder,while the velocity-gradient effect associated with a change in^*is of less importance.Moreover,the interventions of the incident flow turbulence weakens the synchronization between the velocity fluctuation in the gap and the elastic-cylinder vibration.In summary,a systematic experimental study on the axial-flow-induced vibration of elastic cylinder in a cylinder cluster is presented.The effect of turbulence intensity on the fluid-structure interaction of elastic cylinder subjected to an axial flow is revealed by the simultaneous measurements of the cylinder vibration and the flow field around the cylinder.Two regimes are identified based on the distinct behaviours in cylinder vibration and flow strucutres,and the coupling mechanism between the cylinder vibration and near-wall flow structures is revealed.The present research has further deepened the understanding of the mechanism of the axial-flow-induced viration and fluid-sructure interaction,which is of important guiding significance for the design and safe operation of nuclear reactors,and also lays a theoretical foundation for the development of advanced nuclear reactor technology.更多还原