Particle Mass Loading Effect on a Two-Phase Turbulent Downward Jet Flow

The particle mass loading effect on the flow structure of a two-phase turbulent jet flow was studied. A particle mass loading ratio ranging from 0 to 3.6 was used as the control parameter. The polystyrene solid particles used had nominal diameters of 210 and 780 μm. The flow Reynolds number, which was based on the pipe nozzle diameter and the fluid-phase centerline mean velocity, was 2 × 10⁴ in the current test. A two-color laser Doppler anemometer (LDA), combined with the amplitude discrimination method and the velocity filter method, was employed to measure the mean velocity distributions for the particle and fluid phases, and the turbulent intensities and Reynolds stresses of the flow. The two-phase jet flow field was measured from the initial pipe exit to 90 D downstream. Another one-component He? Ne laser LDA system was also applied to obtain the energy spectra and temporal correlations of the two-phase jet flow.     

Pipe flow measurement by using a side-scattering holographic particle imaging technique

A side scattering holographic particle imaging technique has been developed and demonstrated to be a capable tool for obtaining good quality images of a particle field in a high Reynolds number pipe flow. Instantaneous three-dimensional velocity components can be measured. The streamwise velocity error is estimated to be about 5%. Limitations of this optical set-up are discussed. The methodology and results presented will be of use for designing a pulsed laser holographic technique for turbulent velocity measurement or particle diagnostics in a pipe flow.     

动态冰浆流动的浓度分布及粘性研究

动态冰浆是一种固-液两相流体。文中采用理论模型研究了动态冰浆在非均质流动情况下的冰晶浓度分布,分析了冰晶浓度、冰浆流速、管道直径、冰晶粒径大小对冰浆的动态粘度的影响。分析表明:在高冰晶浓度、低流速情况下,冰浆的平均粘度不仅和冰晶浓度和载流溶液的粘度相关,还受到冰浆流速、管道直径和冰晶颗粒大小的影响。     

弯管内气液固三相流中液膜区流场的PIV测量

为了深入认识螺旋管内多相流相分离现象,应用粒子图象测速仪(PIV),对组合弯管内气水砂三相流底部水平段和上升段中液膜区的流场进行了测量。研究表明:底部水平段流动主流速度分布比较均匀,颗粒跟随流体运动;二次流十分微弱,颗粒在离心力作用下由内弯侧向外弯侧运动;速度脉动强烈,不利于相分离。上升段中流动受到重力的阻碍,同底部平段相比主流速度降低,离心力作用减弱,颗粒径向时均速度较低;流动的间歇性更强,两相速度脉动更剧烈。     

90°弯管内冰浆流动特性数值模拟

基于欧拉法建立了冰浆流动的混合模型,对冰浆在90°弯管内的流动特性进行了数值模拟研究,获得了弯管内冰浆的流场和冰晶颗粒的运动轨迹,探讨了弯管管径、曲率半径及冰浆的流速、浓度参数对弯管内冰浆压降的影响,并对弯管压降的模拟结果与实验结果进行对比,两者吻合较好。结果表明:在计算参数范围内,弯管压降随冰浆流速、浓度及弯管曲率半径的增大而增大,随弯管管径的增大而减小;冰浆在弯管内流动形成二次流现象,两个漩涡区域出现在弯管截面两侧;漩涡导致部分冰晶颗粒的运动轨迹发生改变,并使其向弯管下方的负压区聚集,增大了冰晶颗粒的碰撞几率。     

固液两相流中微对流强化的机理分析与数值模拟

本文对分散型固液两相混合物层流管流中非均匀剪切力场导致的微对流现象以及由此引起的导热系数增强效应作了机理和影响因素分析,认为除速度分布、颗粒浓度和粒径以外,还存在颗粒形状、粒径分布,壁面热流方向、颗粒表面性质及其与载流介质间的相容性等多个影响因素.模拟计算表明,由微对流导致的对流换热强化与流体在管壁面上的表观导热系数强化具有相同的数量。     

Nonlinear dynamics of cantilevered extensible pipes conveying fluid

In this paper the nonlinear planar dynamics of a fluid-conveying cantilevered pipe is investigated. The centreline of the pipe is considered to be extensible; i.e., coupled longitudinal and transverse displacements are considered. The extended version of the Lagrange equations for systems containing non-material volumes is employed to derive the equations of motion, resulting directly in a set of coupled nonlinear ordinary differential equations. The pseudo-arclength continuation technique along with direct time integration are used to solve these equations. Bifurcation diagrams of the system are constructed as the flow velocity is increased; these diagrams are supplemented by time traces, phase-plane portraits, and fast Fourier transforms for some sets of system parameters. As opposed to the case of an inextensible pipe, an extensible pipe elongates in the axial direction as the flow velocity is increased from zero; depending on the system parameters, this static elongation can be considerable. At the critical flow velocity, the system loses stability via a supercritical Hopf bifurcation, emerging from the trivial solution for the transverse displacement and leading to a flutter.     

Phase velocities of plane waves in a pipe with a flow whose velocity varies along the radius

The phase velocities of plane waves in a pipe filled with a moving acoustic medium are studied for different laws of flow velocity variation along the pipe radius. The wave equation is solved by the discretization method, which breaks the entire pipe volume into individual cylinders under the assumption that, within each of the cylinders, the flow velocity of the medium is constant. This approach makes it possible to reduce the solution to the wave problem to solving Helmholtz equations for individual cylinders. Based on boundary conditions satisfied at the boundaries between neighboring cylinders, a homogeneous system of linear algebraic equations is obtained. From this system, with the use of the scattering matrices, a simple dispersion equation is derived for determining the phase velocities of plane waves. The stability of the numerical solution to the dispersion equation with respect to the number of cylinders is investigated. The phase velocities of quasi-homogeneous and inhomogeneous waves in a pipe are numerically calculated and analyzed for different velocities of a moving medium and different laws of flow velocity variation along the radius. It is shown that the variation that occurs in the phase velocity of a homogeneous plane wave in a pipe due to the motion of the medium is identical to the mean flow velocity for different laws of flow velocity variation along the radius. For inhomogeneous plane waves, the phase velocity increment exceeds the mean flow velocity several times and depends on both the law of wave amplitude distribution along the radius and the law of the flow velocity variation along the radius.     

Numerical Simulation Study on Flow Laws and Heat Transfer of Gas Hydrate in the Spiral Flow Pipeline with Long Twisted Band

The natural gas hydrate plugging problems in the mixed pipeline are becoming more and more serious. The hydrate plugging has gradually become an important problem to ensure the safety of pipeline operation. The deposition and heat transfer characteristics of natural gas hydrate particles in the spiral flow pipeline have been studied. The DPM model (discrete phase model) was used to simulate the motion of solid particles, which was used to simulate the complex spiral flow characteristics of hydrate in the pipeline with a long twisted band. The deposition and heat transfer characteristics of gas hydrate particles in the spiral flow pipeline were studied. The velocity distribution, pressure drop distribution, heat transfer characteristics, and particle settling characteristics in the pipeline were investigated. The numerical results showed that compared with the straight flow without a long twisted band, two obvious eddies are formed in the flow field with a long twisted band, and the velocities are maximum at the center of the vortices. Along the direction of the pipeline, the two vortices move toward the pipe wall from near the twisted band, which can effectively carry the hydrate particles deposited on the wall. With the same Reynolds number, the twisted rate was greater, the spiral strength was weaker, the tangential velocity was smaller, and the pressure drop was smaller. Therefore, the pressure loss can be reduced as much as possible with effect of the spiral flow. In a straight light flow, the Nusselt number is in a parabolic shape with the opening downwards. At the center of the pipe, the Nusselt number gradually decreased toward the pipe wall at the maximum, and at the near wall, the attenuation gradient of the Nu number was large. For spiral flow, the curve presented by the Nusselt number was a trough at the center of the pipe and a peak at 1/2 of the pipe diameter. With the reduction of twist rate, the Nusselt number becomes larger. Therefore, the spiral flow can make the temperature distribution more even and prevent the large temperature difference, resulting in the mass formation of hydrate particles in the pipeline wall. Spiral flow has a good carrying effect. Under the same condition, the spiral flow carried hydrate particles at a distance about 3–4 times farther than that of the straight flow.     

Flow-induced oscillations of a cantilevered pipe conveying fluid with base excitation

It is known that a plain cantilevered pipe conveying fluid loses its stability by a Hopf bifurcation, leading to either planar or non-planar flutter for flow velocities beyond the critical flow velocity for Hopf bifurcation. If an external mass is attached to the end of the pipe (an end-mass), the resulting dynamics become much richer, showing 2D and 3D quasiperiodic and chaotic oscillations at high flow velocities. In this paper, a cantilevered pipe, with and without an end-mass, subjected to a small-amplitude periodic base excitation is considered. A set of three-dimensional nonlinear equations is used to analyze the pipe?s response at various flow velocities and with different amplitudes and frequencies of base excitation. The nonlinear equations are discretized using the Galerkin technique and the resulting set of equations is solved using Houbolt?s finite difference method. It is shown that for a plain pipe (with no end-mass), non-planar post-instability oscillations can be reduced to planar periodic oscillations for a range of base excitation frequencies and amplitudes. For a pipe with an end-mass, similarly to a plain pipe, three-dimensional period oscillations can be reduced to planar ones. At flow velocities beyond the critical flow velocity for torus instability, the three-dimensional quasiperiodic oscillations can be reduced to two-dimensional quasiperiodic or periodic oscillations, depending on the frequency of base excitation. In all these cases, a low-amplitude base excitation results in reducing the three-dimensional oscillations of the pipe to purely two-dimensional oscillations, over a range of excitation frequencies. These numerical results are in agreement with the previous experimental work.     

New Equation for Predicting Pipe Friction Coefficients Using the Statistical Based Entropy Concepts

In general, this new equation is significant for designing and operating a pipeline to predict flow discharge. In order to predict the flow discharge, accurate determination of the flow loss due to pipe friction is very important. However, existing pipe friction coefficient equations have difficulties in obtaining key variables or those only applicable to pipes with specific conditions. Thus, this study develops a new equation for predicting pipe friction coefficients using statistically based entropy concepts, which are currently being used in various fields. The parameters in the proposed equation can be easily obtained and are easy to estimate. Existing formulas for calculating pipe friction coefficient requires the friction head loss and Reynolds number. Unlike existing formulas, the proposed equation only requires pipe specifications, entropy value and average velocity. The developed equation can predict the friction coefficient by using the well-known entropy, the mean velocity and the pipe specifications. The comparison results with the Nikuradse’s experimental data show that the R2 and RMSE values were 0.998 and 0.000366 in smooth pipe, and 0.979 to 0.994 or 0.000399 to 0.000436 in rough pipe, and the discrepancy ratio analysis results show that the accuracy of both results in smooth and rough pipes is very close to zero. The proposed equation will enable the easier estimation of flow rates.     

管流中注入粒子的非定常波系的数值研究

使用二维有限体积方法,对在管流中固定位置处注入静止固体粒子的可压缩含灰气体流动进行数值模拟,讨论流场和粒子在过程中的耦合,研究质量增加和热量变化所产生的非定常波系,分析物理参数在过程中的变化.结果表明,在添质和加热过程中,流场会产生不同类型和不同强度的非定常波,在分析其物理规律的同时,讨论添质和加热相互作用导致的波系间转换,最后求解流场中各区域的热力学参数,得到不同的流场速度和粒子温度情况下各非定常波波强的相图,定量解释改变参数引起的非定常波变化规律.     

螺旋管内气液固三相流颗粒相分布规律

为了深入认识螺旋管多相流相分离现象,并为新型螺旋管除砂器设计提供指导,本文应用马尔文粒度仪,测量了螺旋管气水砂三相流底部水平段液膜中的颗粒浓度和粒度分布。研究表明:在泡状流和分层流条件下,螺旋管底部水平段可形成稳定的连续液膜流动;在宽广的气速范围内,液膜中的颗粒浓度分布规律均为内弯侧较低、外弯侧较高,说明螺旋管除砂器对于实际生产中流动工况的变化具有良好的适应性;泡状流中提高气速有利于分离;分层流中在中等气速条件下外弯侧颗粒浓度最大,中等气速是相分离的最佳操作工况。     

Inline ultrasonic rheometry by pulsed Doppler

This will be a discussion of the non-invasive determination of the viscosity of a non-Newtonian fluid in laminar pipe flow over the range of shear rates present in the pipe. The procedure used requires knowledge of the flow profile in and the pressure drop along a long straight run of pipe. The profile is determined by using a pulsed ultrasonic Doppler velocimeter. This approach is ideal for making non-invasive, real-time measurements for monitoring and control. Rheograms of a shear thinning gel will be presented. The operating parameters and limitations of the Doppler-based instrument will be discussed. The most significant limitation is velocity gradient broadening of the Doppler spectra near the walls of the pipe. This limitation can be significant for strongly shear thinning fluids (depending also on the ratio of beam to pipe diameter and the transducer's insertion angle).     

单帧单曝光图像法测量气固两相流速度场

本文提出一种基于单帧单曝光图像的气固两相流固相颗粒的速度场测量方法。通过控制相机的单次曝光时间获得流场中颗粒的单帧运动模糊图像,运用分水岭算法分割图像,提取颗粒,由自相关函数获得各颗粒的速度大小和方向,重建二维速度场。利用该方法对玻璃珠在空气中重力沉降的速度测量结果与理论值基本一致,矢量场与颗粒运动轨迹相符,说明该方法可以用于气固两相流速度场的测量。研究发现使用片光源比背光源能够获得更加准确的速度值。     

轴流压缩机叶栅内固体微粒沉积的数值研究

本文针对轴流压缩机叶栅内固体微粒沉积的问题,采用计算流体动力学(CFD)软件对压缩机叶栅内的气固两相流动进行了模拟。文中首先采用不同的湍流模型和不同的壁面处理方法计算了垂直圆管内固体微粒的沉积,并与实验数据进行了对比。在此基础上,研究了轴流压缩机叶栅内不同直径粒子在叶片压力面和吸力面的沉积规律;且研究了不同工况对粒子沉积的影响。     

Visualization of molten pools and invisible laser beam profiles using an ultraviolet CCD camera

Experiments were conducted on the effects of a wall distance and velocity ratio of suction flow to injection flow on the flow and heat transfer characteristics of a circular impinging jet accompanying an annular suction flow. As a result, it is found that in the case of accompanying suction flow, a higher Nusselt number can be obtained compared with in the case without suction flow, under a condition of the wall distance within eight times of injection pipe diameter from the near pipe exit edge. In addition, when the effect of velocity ratio is examined at a fixed arbitrary wall distance, it is found that there exists an optimum velocity ratio where the Nusselt number becomes the maximum. It is shown that these heat transfer characteristics are closely associated with the fluctuating velocity and the mean velocity in the two-dimensional velocity field observed by Particle Image Velocimetry (PIV).     

托卡马克真空室内线圈水冷管道接头强化二次流的数值研究

基于计算流体力学(CFD)理论,研究了不同曲率半径的螺旋导流片的托卡马克真空室内线圈水冷管道接头。利用湍流数值模拟方法,分析了线圈管道接头导流片曲率半径比、冷却水入口流速对线圈管道内流体平均雷诺数分布的影响。结果表明,不同导流片曲率半径比的线圈管道内的流体雷诺数分布曲线相似,平均雷诺数随入口流速的增加而增大,管道接头出口雷诺数随导流片曲率半径比的增大而减小,导流片曲率半径比小的管接头更适用于线圈水冷曲线管的二次流强化。此外,还为导流片曲率半径比为0.2的管接头拟合了管接头出口雷诺数与入口流速的关系式,为进一步研究类似于托卡马克真空室内线圈管道的曲线管接头的二次流强化提供理论基础。     

Experimental study of relative velocity fluctuations in turbulence

Photon correlation spectroscopy was used to explore turbulent pipe flow behind a grid. Measurements of the light intensity correlation function indicate that the probability distribution function of the relative velocity in turbalent flow is well approximated by a product of a lorentzian function and a gaussian-like function.     

Imaging the velocity profiles in tubeless siphon flow by NMR microscopy

We report on the use of NMR micro-imaging to observe flow within a tubeless siphon. The flow is maintained in a visco-elastic liquid of high extensional viscosity, namely 0.5% w/v 8 million Dalton polyethylene oxide in water. The velocity profiles reveal a significant velocity gradient in the vertical direction as well as a transition from near-Poiseuille flow at the pipe entrance to plug flow far from the pipe entrance towards the base of the tubeless siphon.