Experimental study of shell side flow-induced vibration of conical spiral tube bundle

Conical spiral tube bundles are widely used in enhancing the heat transfer via the flow-induced vibration in heat exchangers. The shell side flow-induced vibration of the conical spiral tube bundle is ...     

MATHEMATICAL ANALYSIS OF TRANSVERSE VIBRATION OF CONICAL SPIRAL TUBE BUNDLE WITH EXTERNAL FLUID FLOW

The conical spiral tube bundle is a new type of heat transfer elements used to enhance heat transfer through flow-induced vibration. The effect of the external fluid flow on the transverse vibration of the conical spiral tube bundle is investigated with a mathematical method proposed in this article. Firstly, the natural vibration of the tube bundle is obtained by the hammering excitation method and the mode shapes of the transverse vibration are discussed. Then the effect of the external fluid flow on the transverse vibration of tube bundle is analyzed by a combination of experimental data, empirical correlations and FEM. The results show that in the frequency range from 0 Hz to 50 Hz, there exist six transverse vibrations. The external fluid flow has a significant effect on the frequency of the tube's transverse vibration, which are decreased by about 18% to 24% when the external fluid flow speed is 0.3 m/s.     

VIBRATION CHARACTERISTICS OF FLUID-STRUCTURE INTERACTION OF CONICAL SPIRAL TUBE BUNDLE

Heat transfer enhancement is achieved by flow-induced vibration in elastic tube bundles heat exchangers.For a further understanding of heat transfer enhancement mechanism and tube structure optimization,it is of importance to study the vibration characteristics of fluid-structure interaction of tube bundles.The finite element method is applied in the study of fluid-structure interaction of a new type elastic heat transfer element,i.e.,the dimensional conical spiral tube bundle.The vibration equation and ele...     

EXPERIMENTAL STUDY OF ENHANCED HEAT TRANSFER BY FLOW-INDUCED VIBRATION OF ELASTIC TUBE BUNDLES

1.　INTRODUCTIONThe flow-induced vibration isa general phenomenon in heatexchangers.Its mechanismconsists of vortex shedding,turbulentbuffeting,fluid elastic excitation,acoustic excitation,static pressure pulsation oftwo-phase-flow,etc.In thisaspect,a large quantity ofwork wasconducted,and many theoretical models and experiential discriminantswere putforward bylots of researchers(see Ref.[1 ] ) .The previous study mostly laid emphasis on the avoidanceof flow-induced vibration,however,its …     

基于本征正交分解的动边界环形缝隙流场诊断分析

缝隙流动的流体应力脉动、流致振动等瞬态现象往往会对水力机械的稳定运行产生一定影响,以往的缝隙流动层流近似求解与边壁脉动压力测量无法对瞬态现象进行全场的定量描述。本文以有压有限域内的动边界环形缝隙为研究对象,对该流场在完全湍流状态下的物理试验结果进行了基于本征正交分解的全场诊断分析。结果表明:流体应力方面,流场前部的雷诺应力迅速增长,在流场中部维持一定幅值,在流场后部迅速沿程递减。主流沿径向的平均对流输运强度,高出同一工况时径向流沿周向的对流输运强度4~7倍,高出主流沿周向的对流输运强度6~14倍;流致振动方面,功率谱密度函数表示的流场流致振动频谱在同一流量时有着较为明显的分区趋势,对于低频段(0~10Hz)与高频段(120Hz以上)环隙宽度较小时功率谱密度较大;对于中频段(10~120Hz)则是环隙宽度较大时功率谱密度较大。对于环隙流场,环隙宽度的减小对于其较大尺度的流致振动抑制作用较强。此外,使用本征正交分解识别出了流场的拟序结构,并且使用低阶模态对雷诺应力进行重构可以较好的估计流场的雷诺应力。     

脉冲波作用下竖直弹性板的水弹性响应

基于线性势流理论,将流场分为3个部分:入射势与反射势部分、辐射势的记忆部分、辐射势的瞬时部分,竖直弹性板的时域振动基于模态叠加法,利用傅里叶与拉普拉斯变换求解流场控制方程,与板的振动方程耦合,推导得出波浪作用下竖直弹性板的时域耦合方程,并利用二级四阶隐式Runge-Kutta法求解方程。首先给定竖直板一个初始弯曲,得到的结果与解析解和数值解结果吻合良好,验证了方法的正确性。其次对脉冲波作用下弹性竖直板的响应进行研究,分析了板的刚度系数、质量系数、脉冲幅值和边界条件对其水弹性响应的影响。研究结果表明,刚度系数对板的振动频率影响很大,脉冲幅值与板的振动幅度正相关,两边固定时对竖直弹性板的疲劳损伤最严重。     

万安水利枢纽底孔坝段中隔墙流激振动响应分析

 研究了万安水利枢纽底孔坝段中隔墙在水流脉动壁压作用下的结构随机振动问题，进行了一种泄流工况下的隔墙结构流激振动响应统计量的理论计算，模拟计算了隔墙－水流－基础耦合系统固有频率对流激振动响应的影响，并对水流脉动壁压随机荷载作用下的结构动力可靠度进行了理论分析。     

水轮机压力脉动的测试分析与评价

近几年来,国内外一些新投入运行的大型电站在稳定性运行方面遇到了不少问题,有的已经解决,有的则还没有找到问题的原因,影响了电站的稳定运行。三峡水电站2003年已有多台机组投入运行,其将来能否安全稳定运行是人们共同关心和担心的问题。针对水轮机的稳定性问题,国内外进行了大量的研究工作,水轮机的压力脉动无疑是最受关注的问题之一。但是,     

Receptivity of plane Poiseuille flow to local micro-vibration disturbance on wall

The receptivity of plane Poiseuille flow to local single-period micro-vibration disturbances with different phases at the top and bottom walls was investigated through direct numerical simulation of three-dimensional incompressible Navier-Stokes equations. Results show that the disturbance presents a symmetrical distribution in the spanwise direction when the micro-vibration on the wall ends, and the initial disturbance velocities and spatial distribution of the disturbance structure are different at the top and bottom walls. The disturbance’s velocity, amplitude, and high- and low-speed streaks increase with time, and the amplitude of streamwise disturbance velocity is larger than those of spanwise and vertical disturbance velocities. However, no significant Tollmien-Schlichting wave was found in the flow field. The number of disturbance vortex cores gradually increases with the disturbance area. High-speed disturbance fluid concentrates near the wall and its normal velocity largely points to the wall, while low-speed disturbance fluid largely deviates from the wall. Furthermore, the streamwise velocity profiles near the top and bottom walls both become plump because of the existence of the disturbances, and the streamwise velocity profiles show a trend of evolving into turbulent velocity profiles. The shear stress near the wall increases significantly. The local micro-vibration disturbance on the wall in plane Poiseuille flow can induce the development of a structure similar to turbulent spots.     

INFLUENCE OF YOUNG'S MODULUS ON DRAG-REDUCTION IN TURBULENT FLOW USING FLEXIBLE TUBES

In order to develop technologies of friction drag reduction with a flexible tube to be used for water transport, experimental studies were carried out on the influence of Young's modulus on the turbulent drag reduction. The friction coefficients of flexible tubes with different Young's modulus were examined by using a sleeve-tube structure. The fluctuating vibration of the outer wall and the fluctuating pressure on the inner wall of the tubes were measured with a laser displacement sensor and a pressure sensor. The results are as follows. The smaller the Young's modulus of a flexible tube and the larger the Reynolds number, the larger the turbulent drag reduction rates become. The transition from laminar flow to turbulent flow can be delayed with an appropriate Young's modulus. Non-dimensional amplitude of fluctuating vibration on the outer wall is smaller than that of a viscous sub-layer thickness, and is positively correlated with the friction drag reduction.     

三峡溢流坝左导墙流激振动有限元计算分析

三峡工程溢流坝泄水时 ,泄洪水流将对导墙产生较强的水流脉动压力和激荡力作用 ,可能诱发结构振动 ,甚至导致工程事故。以左导墙为研究对象 ,在总结了水弹性模型流激振动试验和相应计算的基础上 ,水弹性振动模型试验实测的脉动压力成果 ,按水弹性相似律进行转化 ,采用逐步积分方法 ,对导墙模型结构和原型结构作流激振动响应分析比较 ,并对点面转换系数进行了探讨 ,最后对导墙的安全度进行了综合性评价 更多还原     

埋地异型供水管段泄漏定位方法

供水管道泄漏时产生泄漏声波,根据泄漏声波到达安装在管道上的两个传感器的时间差,可以估计出泄漏位置。泄漏声波在管道中的传播速度与管道材料、内径和壁厚等有关。当泄漏发生在由不同类型管道组成的管段上时,用平均声速计算泄漏位置会增大定位的不确定度。借助于供水管网信息化提供的地下管线详实信息,根据各段管道的长度和声速可以更准确地估计出泄漏位置。介绍了异型管段泄漏定位的计算方法,给出一个检测实例和算法的流程。     

溢流面板坝泄槽锚杆设计参数敏感性分析

针对设锚杆的溢流面板坝泄槽流激振动性能复杂的特点,建立拟三维仿真模型,采用时域分析法对锚杆设计参数的敏感性进行了研究。结果表明:在一定的水流限制流速条件下(v≤40 m/s),在影响溢流面板坝流激振动性能的3个锚杆设计参数中,锚杆布设间距对关键点的拉应力和接缝处法向变形响应幅值影响最大,锚杆布设长度及直径影响相对较小。大致规律为:关键点的应力随锚杆布设间距和锚杆直径的增加而增大,随布设长度的增大而减小;关键点的法向变形随板后布设长度和锚杆直径的增加而增大,随锚杆布设间距的增加而减小;3种因素存在显著性顺序:锚杆布设间距,布设长度,锚杆直径。研究成果可为同类坝型泄槽锚杆参数的设计提供指导。     

分布随从力作用的双参数地基上悬臂管稳定性研究

为了对分布随从力作用时双参数地基上悬臂管稳定性进行分析,利用Euler-Bernoulli梁模型创立输流管道的运动微分方程,然后运用传递矩阵法进行求解。通过分析悬臂输流管的无量纲复频率和失稳时临界流速间的关系,在地基刚度取4种不同值情况下研究悬臂管道受分布随从力和流体流速作用时的振动情况。结果表明①地基刚度取值一定时,悬臂管道受分布随从力和流体流速影响时的振动特点大不一样;②无量纲分布随从力与流体流速取值一定时,管道系统的振动状况随着地基刚度增加而更加稳定,相比线性刚度的影响剪切刚度的作用尤为突出。     

闸阀失效诱发水库输水涵管振动探测与分析

为了对某水库输水涵管振动原因进行分析,首先采用振动监测仪对管道不同位置振动特性进行监测,分析管道不同位置振动变化规律,初步确定了振源位置;其次通过管道机器人对管道内部进行探测,结合已有理论基础初步分析了管道振动的内因;最后通过现场开挖,分析了管道振动的外因。结果表明：闸阀位置处质点振动峰值速度、主频、峰值加速度和峰值位移均明显大于其他测点,闸阀前后振动特性基本对称,推测闸阀为主要的振动源;闸阀处各方向质点振动峰值速度、峰值加速度和峰值位移均为垂向＞切向＞径向,推测闸阀的主要振动方向为垂向;输水涵管闸阀仅能开启至设计最大开度的1/3位置处,当闸阀在此种小开度开启时,产生的垂向流激振动是输水涵管振动的主要原因;闸阀附近土体松散,且未设置镇墩,无法较好地约束输水涵管变形,从而导致振动加剧。     

水力发电引水系统水体共振的数值模拟

分析了某水力发电厂水轮机组在紧急关机试验过程中出现的异常强烈的振动现象。考虑水为可压缩黏性流体，采用瞬态动力响应仿真软件，按照原型参数对水体共振进行数值模拟。研究了冲击载荷引起的水体自由振荡信号，得到水体振荡主频率。在引水管末端用平板的横向振动引入压强扰动，观察到强迫振动频率接近水体主频率时发生共振，而且在整个引水管内的水体都有较强烈响应，证实了水体共振发生的可能性。对共振发生时的压强信号进行小波分解，发现引水系统的压强信号中响应幅度最大的小波分量的频率低于强迫振动频率。计算结果还表明水的黏性和壁面粘附条     

STUDY ON TURBULENCE FEATURES NEAR AN OSCILLATING CURVED WALL

In pursuit of possibly true turbulent characters and for exploring a change in turbulence structures near an oscillating flexible wall-curved surface, a sinusoidal oscillation mode was forced to a curved wall, whose vibrations disturbed the flow with an interacting effort between the fluid and the structure. The methodology used was the Large Eddy Simulation (LES) with fluid-structure interaction. The oscillating configuration was on a Fourier sinusoidal mode from the measurements of a Francis hydro turbine blade vibration. The effects of the vibration on the skin friction coefficient, vortices, turbulent coherent structures, and other statistical quantities were studied. The results showed that the streamwise velocity gradient along the normal direction and the normal velocity gradient along the spanwise direction were considerably increased within the viscous sublayer because of the oscillating wall, which additionally caused the low speed streaks to stay away from the wall and the high-momentum flows to be toward the wall. As a result, the streamwise vortices were much more elongated along the downstream to get an energy balance, and the wall skin friction coefficient or the wall friction velocity rose up.     

DRAG REDUCTION EFFECT OF COUPLING FLEXIBLE TUBES WITH TURBULENT FLOW

To analyze the mechanism of drag reducing effect by coupling flexible tubes with turbulent flow, based on experimental examination of more obvious turbulent drag reduction effect in flexible tubes than in rigid tubes, experimental investigation was performed on the effect of turbulent drag reduction, fluctuating vibration characteristics of flexible tube and the correlations by using a double-tube system and laser displacement sensor. The results are as follows： with the decrease of the thickness of the flexible tubes, the root mean square of fluctuating amplitude of the outer wall of the tubes increases, and the non-dimensional burst period increases, resulting in the increase of the reduction rate of drag coefficient by coupling flexible tubes with turbulent flow. At applied pressure-balanced air on the outer wall and the Reynolds number of about 1.75×10^4, the non-dimensional burst periods of the flexible tubes with the thickness of 2 mm, 3 mm, 4 mm are 141, 126, 105, respectively.     

虹吸式出水管虹吸形成过程的壁面压力及脉动特性

通过物理模型试验测量虹吸式出水管在虹吸形成过程中典型断面的压力过程线，采用邻域平均法提取脉动压力数据，采用统计特征和短时傅里叶变换信号处理方法分析时均和脉动压力特征。结果表明：管壁时均压力沿水流方向先减小后增大，驼峰段的上壁面时均压力随着流量增大逐渐大于下壁面；虹吸形成过程中，压力脉动呈正偏态分布，均方差沿水流方向不断降低；压力脉动主要由水泵旋转和水气运动引起，频率在0～30 Hz之间，主频与水泵转频相近；相比虹吸稳定流阶段，水力驱气阶段存在的气囊压缩和释放过程使得压力脉动频率及幅值上升，接近泵站系统自振频率，容易产生结构振动，需要通过设计和运行的优化减少该阶段的持续时间。     

The experiment and analysis of transitional flow in pipe

The transitional flow in a pipe is important for delivery, but its characteristics remain to be explored. In this paper, the two-dimensional laser Doppler velocimetry(LDV) is used for the study, focusing on the attenuation characteristics of the axial velocity, the variation of the velocity gradient, the effect of the angle between the axis and the resultant velocity vector, and the relationship between the energy coefficient and the flow state. The attenuation characteristics of the axial velocity along the radial direction are obtained. It is shown that with the increase of the Reynolds number, the change rate of the velocity gradient slows down with a similar distribution, and a rapid decrease is seen in the near wall region. The amplitude and the frequency of the angular variation are obviously improved with the increase of the Reynolds number. The instability of the velocity field is enhanced with the increase of the energy coefficient.