二维双圆柱论文：二维串列双圆柱诱导振动及传热特性研究.doc

二维双圆柱论文：二维串列双圆柱诱导振动及传热特性研究【中文摘要】早在20世纪70年代,振动强化换热就已引起人们的关注,但由于受到技术的限制,换热器管束的有效振动的实现存在一定的难度,因此学术界没有对此展开过多的研究。近年来,随着科学技术的发展,振动的实现方法也得到发展,振动强化换热这一课题也在逐渐兴起,而如果管束的振动需要外来能量提供激励,换热器在提高换热的同时,也需要消耗外来的能量,因此,从节能的角度来讲,这种靠外部激励的方式来达到振动并不是最有效的；弹性管束结构的提出很好的解决了这一问题,弹性管束即是在流体诱导下管束产生振动,这种振动既不会对管束产生破坏,又可以提高管束的换热系数,且不需要消耗外来的能量,从而达到节能降耗的。基于这一背景,本文对双圆柱的振动强化换热及流体诱导振动响应进行了研究,所得到的结论可以为弹性管束换热器的设计提供一定的依据,主要研究内容分如下：首先针对串列双圆柱的不同排列方式对对流换热效果的影响进行了数值模拟,计算了不同间距比下双圆柱的面均nu数,并分析了不同间距比l/d(l为双圆柱的中心距,d为圆柱直径)下双圆柱绕流时的速度场和温度场的协同情况,得到了静止和振动条件下的双圆柱换热效果及协同角随间距比变化的规律,双圆柱排列间距不同时,换热效果不同,当间距比l/d3.5后,协同角减小,换热效果明显增强且随后趋于平稳,因此,在对换热管束的排列间距进行设计时,可以考虑选取l/d3.5。基于间距比与换热的关系,建立换热效果较好的间距比l/d=4.0的二维串列双圆柱数值计算模型,对其进行了振动强化换热分析,分别考虑了振动方向、振动频率及振幅大小对换热效果的影响。数值分析结果表明,当圆柱以不同振动方向振动时,换热效果相差不大,振动方向对速度场和温度场协同程度影响较小；而双圆柱振动频率及振幅大小对换热效果的影响则很明显,双圆柱强化换热百分比随振幅和频率的增大而增大,振幅和频率的增大也使得场协同程度得到提高,且在较高频率时,振幅对圆柱的强化换热百分比的影响更显著。对间距比l/d=4.0的二维串列双圆柱在不同流速下的诱导振动响应进行了分析,得到了双圆柱横向振动位移幅值随流速变化的规律,在本文计算范围内,双圆柱的诱导振动位移幅值存在一个最大值,该最大值出现在约化速度5.676左右,当入口流速低于此值时,位移幅值随着流速的增大而增大,而当入口流速高于此值后,位移幅值则随流速的增大而减小。同时,双圆柱在不同流速下会发生驰振、拍振及单一涡激振动,随着流速的增加,双圆柱完成驰振-拍振-涡激振动的转化。驰振时,双圆柱振动频率小于涡脱落频率；当发生拍振时,振动会存在多个相互竞争的频率；当双圆柱做单一的涡激振动时,横向振动频率和涡脱落频率相等。对间距比l/d=4.0的二维串列双圆柱不同结构参数下的诱导振动进行了数值分析,主要考虑了结构刚度和质量比对流体诱导振动的影响。数值模拟结果表明,随着刚度的减小,位移幅值增大,但当刚度减小到一定值后,位移幅值基本保持不变,此时双圆柱的诱导振动出现了“自限定”现象,而当刚度增加时,双圆柱横向振动频率随着刚度的增加而减小,振动规律也由规则简谐曲线转变为复杂的振动曲线,振动频率逐渐偏离涡脱落频率；质量比对圆柱横向振动位移幅值的影响是非线性的,质量比较小时,圆柱做规则的简谐振动,位移幅值较大,振动频率与涡脱落频率相等,随着质量比的增大,位移幅值减小,振动频率开始小于涡脱落频率,振动规律变为复杂的周期振动。【英文摘要】vibrating in heat transfer enhancement was paid attention in 70s last century. with the development and progress of technologies, the subject was mentioned more and more. the research in heat transfer mechanism of vibrating surface would be a theory to direct the practice. in the present dissertation, the effects of tube vibration of the two 2-d circular cylinder on convective heat transfer was investigated, and the flow-induced vibration of the cylinders was analyzed.in the first part, both the static and vibrating cylinders were analyzed at different spacing ratios via the fluent software to find the relationship between spacing ratios and convective heat transfer of the two cylinders. the field synergy theory was used to analyze the synergy of the velocity and temperature field in different spacing ratios. the results show that there exists a threshold of spacing ratio. when the spacing ratio of the two cylinders is larger than the threshold, heat transfer of the two cylinders enhanced, and vice versa. therefore, the spacing ratio of the heat exchanger can be l/d3.5 in the design of heat exchanger.in the second part, the effect of vibration on heat transfer of the two 2-d cylinders was discussed. the vibration direction,the frequency and the amplitude of the oscillating circular cylinders were studied in this part. the numerical simulation results show that the different vibration direction of the cylinders have little effect on heat transfer and the synergy of the velocity field and the temperature field were almost the same; when the frequency and the amplitude increased, the heat transfer of the cylinders enhanced, and vice versa. in the third part, the numerical simulation of flow-induced vibration of the two 2-d cylinders with transverse motion was conducted. the relationship between the magnitude of inlet velocity of the flow and the flow-induced vibration was studied.the numerical simulation results show that the amplitude of the vibration has a maximum with the inlet velocity of the flow equals to 5.676. when the velocity is lower than 5.676, the amplitude was smaller than the max, and when the velocity is larger than 5.676,the amplitude was also decreased.at low inlet velocity, the two 2-d cylinders galloped, and the frequency was smaller than the vortex shedding frequency. when the inlet velocity increased, the beat phenomenon could be discovered on the cylinders, and the frequency of the flow-induced vibration was complex. when the vortex-induced vibration happened, the frequency of the cylinders equaled to the vortex shedding frequency.in the fourth part, the flow-induced vibration of two 2-d cylinders at different stiffness and mass ratios were investigated. the results show that the amplitude of the cylinders increased with the stiffness decreased, and when the stiffness decreased to a level, the amplitude stabilized at a constant. the frequency of the cylinders was smaller than the vortex shedding frequency while the stiffness increased and the vibration becomes more complex. the vibration of the cylinders was harmonic at small mass ratio, and the frequency equaled to the frequency of the vortex shedding. as the mass ratio increased, the amplitude would be lower, and the frequency would be smaller than the vortex shedding frequency, the vibration became more complex.【关键词】二维双圆柱 对流换热 数值模拟 场协同 流体诱导振动【英文关键词】two 2-d cyliders convective heat transfer numerical simulation field synergy flow-induced vibration【目录】二维串列双圆柱诱导振动及传热特性研究目录5-7摘要7-9abstract9-10第1章 绪论11-191.1 课题研究的背景与意义11-121.2 振动强化换热研究现状12-141.3 流体诱导振动研究现状14-161.4 场协同理论发展概况16-171.5 本文研究内容17-19第2章 不同排列间距下二维串列双圆柱对流换热分析19-292.1 引言192.2 数值计算模型及网格划分19-222.2.1 数学模型和物理模型19-212.2.2 边界条件与网格划分21-222.3 计算结果及场协同分析22-272.3.1 不同间距比的静止双圆柱换热22-242.3.2 沿流向振动的双圆柱在不同间距比下的换热24-262.3.3 场协同分析26-272.4 本章小结27-29第3章 二维串列双圆柱振动强化换热分析29-433.1 引言293.2 不同振动方向下双圆柱振动强化换热分析29-353.2.1 计算参数29-303.2.2 换热效果及场协同分析30-353.3 振幅和频率对双圆柱强化换热影响分析35-413.3.1 计算参数353.3.2 换热效果及场协同分析35-413.4 本章小结41-43第4章 二维串列双圆柱在流体不同流速作用下的诱导振动分析43-594.1 引言434.2 计算模型及参数设定43-464.2.1 计算模型43-454.2.2 计算参数及运动控制方程45-464.3 计算结果分析46-574.3.1 流体入口速度对双圆柱横向幅值的影响分析46-484.3.2 位移响应和加速度响应分析48-574.4 本章小结57-59第5章 串列