【作者】 王越；

【导师】 谭蔚； 周文学；

【作者基本信息】 天津大学 ， 工程（专业学位）， 2023， 博士

【摘要】 在绕管式热交换器中,相邻管层反向绕制的管束在螺旋线的轴向截面中管束排布结构不断变化,湍流使管束壳侧流动呈不稳定状态,绕管管束与流体耦合的振动形式没有明确,导致反向绕制绕管管束的流致振动安全预测与评估无据可依。因此,本文依据绕管式热交换器中缠绕管的约束方式将其划分为曲管与绕管,采用实验验证、数值模拟和理论分析的方法,研究了曲管与绕管基频的计算方法,给出了绕管管束的管间横向流速U_gap的计算公式,揭示了管束结构参数对漩涡脱落频率的作用机制。提出了湍流抖振主频率的半经验公式和流体力的归一化包络谱,研究了管束流体弹性不稳定性机理,实现了反向绕制绕管管束的固有振动特性的估算和流致振动机理的阐释。设计搭建了曲管与绕管固有频率的模态实验系统和绕管管束流致冲击振动实验系统,用于验证模型的可靠性,揭示几何参数对换热管固有频率的影响规律,探究绕管管束面内方向与面外方向的振动响应。设计了一套用于测定曲管与绕管固有频率的模态实验系统,验证了模态分析模型的可靠性,得到了几何参数对换热管固有频率的影响规律。为了获取管束壳侧流动特征与涡流结构,探究管束结构参数对附加质量系数的作用机制,分别建立了分离涡模拟（DES）三维流场流动模型和剪切应力输运模拟（SST-SAS）三维衰减振动模型,并通过实验和相关文献数据验证了模型的鲁棒性。采用绕管管束流致振动冲击振动实验系统,研究了绕管在水流冲击下的面内方向与面外方向的振动响应,构建了升力与曳力归一化力谱,证明了SST-SAS三维流固耦合模型的合理性。基于理论推导、模态分析和三维流固耦合模型,提出了曲管与绕管基频的计算方法,讨论了几何参数（曲管参数:曲管的直管部分的长度H₁、管板上的管孔与中心轴之间的距离R₁、曲管的轴向高度H、绕管半径R₂和曲管的投影与俯视图中径向的夹角θ;绕管参数:螺旋角α、支撑数S、匝数N和R₂）对基频的影响,揭示了结构参数对附加质量系数C_m的作用机制。研究表明,H₁、H、R₂和θ增大时,曲管基频f₁逐渐减小;而几何参数R₁增大时,f₁则增大。当α、N和R₂增大时,绕管基频f₂逐渐下降,但α对f₂的影响不明显;而几何参数S增大时,f₂陡然增大。曲管与绕管的前三阶阵型均主要发生弯曲变形,与计算方法中的假设相符,证明了假设的合理性。构建了两级交互作用表,表明H对f₁有显著影响,R₂对f₁有一定的影响;S和R₂对f₂有明显的影响,并且证明了参数的独立性。相邻管层间节径比a、同层绕管节径比b和α增大,面内与面外方向的频率比和C_m均减小。绕管管束越紧凑,C_m越大。将壳侧流动与管束振动响应解耦,提出了U_gap计算公式,从结构参数维度,研究了壳侧整体流场特性和局部涡流结构的变化,获取了不同结构参数相应的漩涡脱落频率,给出了St推荐值。基于面积体积加权方法,根据U_gap的正交分解,给出了U_gap计算公式。采用Q准则探究了壳侧整体流场特性,根据Kolmogorov的-5/3定律证明了管束壳侧流动发展为湍流。由于绕管管束的不对称性与α的存在,速度云图不对称,与直管管束不同。涡流出现在同层换热管间隙,并且沿管伸长方向发展,在管表面形成沿壁面流动的边界流,遇涡流汇入或者掠过。采用功率谱密度（PSD）、连续小波分析（CWT）与多峰高斯拟合（MGDA）方法,揭示了结构参数对漩涡脱落频率的影响规律,对于紧凑排布,不需考虑漩涡脱落机理;其余排布方式考虑该机理。随着a与b的增大,St数逐渐减小。基于三维流固耦合模型,创新性地提出了湍流抖振主频率f_t的计算公式和归一化随机激振力谱,明确了随机激振力的变化特征,揭示了绕管管束的流体弹性不稳定性机理,获取了临界流速的半经验公式。利用在不同排布结构中监测管所受随机激励的PSD,获得对应各排布结构的f_t,拟合得到K_t,给出了f_t计算公式。结构参数a主要决定了力系数的大小,a越小,系数越大;b与α主要影响系数的波动幅度,b越小、α越大,系数波动幅度越大。归纳了换热管相对位置、Re数与管束排布结构对流体力谱的作用机制,得到了随机激振力归一化包络谱。管束排布越紧凑,换热管的振动响应越大,振幅波动越剧烈;α增大,前排管与后排管振动响应的差距变小,振幅略有增大。随着折合流速U_r增大,两方向上的振幅逐渐增大,而面外方向的振幅明显大于面内方向,面外方向上率先发生流体弹性不稳定性。基于准静态模型提出了相邻管层反向绕制绕管管束的流体弹性不稳定性临界流速的半经验公式U_c/f_nd=6.97（2πmζ/ρd²）^0.5。本文的研究结果揭示了反向绕制绕管管束的固有振动特性和流致振动机理,为绕管式热交换器管束的结构设计与流致振动安全校核奠定了理论基础,对绕管式热交换器的设计与应用具有重要意义。更多还原

【Abstract】 The bundle arrangement of adjacent layers wound in the opposite direction for Coil-wound heat exchanger is constantly changing in the axial section of the helix.In addition,turbulence makes the fluid in the shell-side present flow instability in the subcritical region,and the vibration form of coil tube bundle coupled to the fluid is not specified.There is no basis for the safety prediction and evaluation of FIV for the bundle wound in the opposite direction.Therefore,according to the constraint of the wound tube in the Coil-wound heat exchanger,it was artificially divided into curved tube and coil tube.By means of experimental verification,numerical simulation and theoretical investigation,the calculation method of fundamental frequencies of curved tube and coil tube was presented.The prediction formula of the transverse velocity between the adjacent tubes was given and the mechanism of the structural parameters of the tube bundle on the vortex shedding frequency was revealed.The semi-empirical formula of the main frequency of turbulent buffeting and the normalized envelope spectrum of the fluid force were presented for the first time.The fluid-elastic instability mechanism of the tube bundle was studied.Finally,the prediction of the natural vibration characteristics and the explanation of FIV mechanism of the tube bundle wound in the opposite direction were realized.In order to prove the reliability of modal and 3-D fluid-structure interaction numerical models,a modal test system and an impact test system about FIV were designed and established.The robustness of 3-D flow model with Detached-Eddy Simulation（DES）and attenuated vibration model was verified by geometric parameters and analysis data in literature.Modal test system was designed to measure the natural frequencies of curved tube and coil tube.The test system was applied to investigate the influence mechanism of geometric parameters on the natural frequency of heat transfer tube and verify the reliability of the modal numerical model.The DES flow numerical model was established to obtain the flow characteristics and vortex structures in the shell-side.Aiming to explore the mechanism of the structural parameters of tube bundle on the additional mass coefficient（C_m）,3-D attenuated vibration model with SST-SAS simulation was built.Then,the validity of the two numerical models was proved by the literature data.The robustness of the 3-D fluid-structure interaction numerical model was verified by measuring the in-plane and out-of-plane vibration responses of coil tubes and constructing normalized force spectra obtained in the coil tube bundle impact test.Based on theoretical derivation,modal model and 3-D attenuated vibration model,the calculation methods of fundamental frequencies of curved and coil tubes were proposed,the independence of geometric parameters was proved,and the influence of structural parameters on C_m was revealed.The calculation methods of fundamental frequencies of curved and coil tubes were given by simplifying the curved and coil tubes as beam element.It was found that when H₁,H,R₂ andθincreased,the fundamental frequency f₁ decreased gradually.And as the geometric parameter R₁increased,so did f₁.Whenα,N and R₂ increased,the fundamental frequency f₂decreased gradually,and the effect ofαon f₂ was not obvious.However,f₂ increased abruptly when S increased.The bending deformation occurred mainly in the first three modes of curved and coil tubes,which was consistent with the assumption in the calculation method and proved the rationality of the assumption.The two-level interaction table was constructed,which showed that H had a significant effect on f₁,and R₂ had a certain effect on f₁.S and R₂ had obvious influence on f₂,and the independence of the parameters is proved.When a,b andαincreased,the frequency ratios of in-plane and out-of-plane and C_m decreased.The tighter the bundle,the larger C_m.Through the analysis of flow characteristics,the prediction formula of the gap transverse velocity,U_gap,was proposed.In terms of the dimension of structural parameters,the overall flow characteristics in the shell-side and the changes of local vortex structures were studied in detail.The corresponding vortex shedding frequencies corresponding to different structural parameters were obtained,and the recommended values of St were given.Based on the area-volume weighting method and the orthogonal decomposition,the time-course gap velocity was obtained,and the prediction formula was derived.Q-criterion was used to explore the overall flow characteristics in the shell-side Kolmogorov’s-5/3 law proved that the flow developed into turbulence.Because of the asymmetry of the bundle and the existence ofα,the flow field was asymmetrical,which was different from the straight tube bundle.The vortex appeared in the gap between tubes of the same layer,and developed along the direction of tube elongation,forming boundary flow along the wall on the surface of the tube,and met another vortex into or over.Power spectral density（PSD）,continuous wavelet transforms（CWT）and multimodal Gaussian distribution approximations（MGDA）were applied to reveal the effect of structural parameters on the vortex shedding frequency.When a×b<1.25,namely compact arrangement,vortex shedding mechanism was not needed to be considered.The mechanism was considered in other arrangements.With the increase of a and b,the recommended value of St decreased gradually.The structural parameters a,b andαall affected vortex shedding.In terms of fluid-structure interaction numerical model with SST-SAS simulation,the main frequency of turbulent buffeting,f_t,and the normalized spectrum of random excitation force were proposed for the first time,the variation characteristics of random excitation force were defined,the fluid-elastic instability mechanism for coil tube bundle was revealed,and the semi-empirical equation for predicting the critical gap velocity was obtained.By using PSD with the random excitation forces of the monitoring tubes in different arrangements,the corresponding f_t was obtained,the fit was obtained K_t,and finally the semi-empirical formula of f_t was given.a mainly determined the magnitude of the force coefficient.The smaller the gap was,the larger the coefficient was.The fluctuation range of the main influence coefficients of b andαwas larger.The smaller b was and the largerαwas,the larger the fluctuation range of the coefficient was.The equivalent power spectral density（EPSD）of random excitation force was analyzed in multiple dimensions,and the normalized envelope spectrum of random excitation force was finally concluded.The more compact the bundle arrangement was,the greater the vibration response of the tubes is,and the more drastic the amplitude fluctuation was.With the increase ofα,the difference of vibration response between front tube and back tube became smaller,and the amplitude increased slightly.With the increase of U_gap,the amplitude in both directions increased gradually,while the amplitude in the out-of-plane was significantly larger than that in the in-plane,and it was the first to occur fluid-elastic instability.Based on the quasi-static model,the semi-empirical equation of the critical gap velocity for the tube bundle was presented as U_c/f_n d=6.97（2πmζ/ρd²）^0.5.The paper addresses the natural vibration characteristics and the FIV mechanism for coil tube bundle with adjacent layers wound in reverse,and lays a theoretical foundation for the structural design of the coil tube bundle and the calculation assessment of FIV of the heat exchanger,which is great significance for the design and application of Coil-wound heat exchanger.更多还原