Buffeting lift forces and local air–water flow aspects around a rigid cylinder

A new experimental programme is conducted in order to relate the characteristics of two-phase flow around a rigid cylinder with the resulting lift forces. The local characteristics of air–water flow measured in the vicinity of the cylinder provide a useful source of information about the effects of flow on the excitation mechanisms. In particular, a selection of relevant parameters has been identified which, with the help of a standard dimensional analysis, may explain the energetic contents of buffeting forces. Among the parameters effective in reducing the data are the flow regime, bubble frequency and gravity forces. In addition, in the range of bubbly regimes, the magnitude of the random forces is found to be related to the local fluctuations of void fraction. Finally, a new formulation is proposed to collapse the dimensionless spectra of the buffeting lift forces in a single characteristic curve. This analysis shows a marked improvement over the collapse of data in comparison with previous normalized models.     

Comparison of the RANS and PDF methods for air-particle flows

Two simulation methods, namely Reynolds-Averaged Navier–Stokes (RANS) equations, and Probability Distribution Function (PDF) are currently widely used for the modeling of multiphase flows. These two approaches are supplemented with appropriate closure equations that take into account all the pertinent forces and interaction effects on the solid particles, such as: particle–turbulence interactions; turbulence modulation; particle–particle interactions; particle–wall interactions; gravitation, drag and lift forces. The two methods have been used in order to simulate the turbulent particulate flow in upward pipes. The flow domain in all cases was a cylindrical pipe and the computations were carried for upward pipe flow. Monodisperse as well as polydisperse mixtures of particles have been considered. In general, the average velocity results obtained from the two methods are in close agreement, because the methods predict well the average velocity distribution of the carrier fluid as well as the solids. Thus, the differences in the average axial velocities predicted by the methods are not substantial. Differences in the turbulence intensity are more significant. A comparison of the numerical results obtained shows the relative importance of retaining the diffusion terms in both the axial and radial directions in the RANS method. Also the comparisons of the results show the relative effect of the lift forces in the distribution of solid particles.     

Phase and Interfacial Tension Behavior of Certain Model Gas Condensates: Measurements and Modeling

This contribution reports on the phase and interfacial tension behavior of some model high-temperature–high-pressure gas condensates. On the one hand these types of gas condensate are becoming a subject of major interest for the oil industry, while on the other their phase and interfacial tension behavior have not been very well studied. For two different model gas condensates, both composed of the three n-alkanes, methane, butane, and decane, experimental results on their fluid phase behavior have been obtained in the temperature region 270 < T (K) < 490 and up to pressures as high as 24 MPa. Also, critical points of the two mixtures have been determined experimentally. Both mixtures show an extended retrograde region. Using the Peng–Robinson equation of state, the phase behavior of the two mixtures was modeled. In addition, the interfacial tension behavior of the model gas condensates was modeled. For that purpose, the Cahn–Hilliard theory was applied in combination with the Peng–Robinson equation of state. Satisfactory results were obtained.     

Hydromagnetic Micropump and Flow Controller. Part A: Experiments with nickel particles added to the water

The novel idea of the Hydromagnetic Micropump and Flow Controller (HMFC) is used in this paper to construct a laboratory setup capable of bidirectional pumping and controlling the flow in microtubes. A laboratory setup, which contains no moving parts, is integrated with a pressure-driven flow setup to make the presented HMFC device. The device operation is based on controllable motion of magnetic particles, added to the carrier fluid, caused by the magnetic field, produced by solenoids located just next to the microtube. The magnitude of these forces is proportional to the strength and gradient of magnetic field which, in turn, is related to the electrical current and arrangement of the solenoids. When switching period is smaller than 0.19 s, the device operates as a pump; while, the flow controlling characteristic is obtained for long switching periods. The flow can be pumped up to 113% of the initial flow rate or can be controlled in a regular and predictable manner.A series of experiments was conducted when nickel particles are added to the water, as the carrier fluid, to examine the impact of different parameters such as switching period and switching mode of solenoids and particle concentration on the performance of the device. Moreover, an ethanol–nickel mixture is used to investigate the impact of carrier fluid on the performance of the device. The role of particle substance is examined comparing results obtained for water–nickel and water–iron mixtures.     

Thermodynamic model of a dense fluid

In this paper we derive an approximate equation of state of a dense fluid in which the thermal pressure is completely determined by the pressure dependence of the volume at 0 ° K. We also consider some generalizations (which take into account the attractive forces of the atoms and the presence of mixtures).Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 1, pp. 119–122, January–February, 1971.     

Influence of an acoustic wave on a system of two spheres in a viscous fluid

In this article we formulate and solve the problem of the influence of radiation forces (forces created by the radiation pressure) on two spheres in a viscous fluid during the transmission of an acoustic wave. On the basis of these forces we investigate the nature of the interaction between the spheres as determined by the mutual disturbance of the flow fields around them as a result of interference between the primary and secondary waves reflected from the spheres. A previously proposed [2] approach is used in the investigations. The radiation force acting on one of the spheres is filtered by averaging the convolution of the stress tensor in the fluid with the unit normal to the surface of the sphere over a time interval and over the surface of the sphere. The stresses in the fluid are represented, to within second-order quantities in the parameters of the wave field, in terms of the velocity potentials obtained from the solution of the linear problem of the diffraction of the primary wave by the free spheres. The diffraction problem is formulated and solved within the framework of the theory of linear viscoelastic solids [6]. The case of an ideal fluid has been studied previously [3–5, 7]. Radiation forces are one of the causes of the relative drift of solid particles situated in a fluid in an acoustic field.S. P. Timoshenko Institute of Mechanics, Academy of Sciences of Ukraine, Kiev. Translated from Prikladnaya Mekhanika, Vol. 30, No. 2, pp. 33–40, February, 1994.     

大跨悬索桥抖振内力响应分析

基于虚拟激励法和有限元法,在频域建立了一种新的桥梁抖振内力响应分析的随机振动方法。该方法与传统随机振动方法相比具有如下两个特点:(1)单元抖振内力响应同时考虑了保留模态多模态耦合产生的动力效应和保留模态外高频模态产生的拟静力效应;(2)单元抖振内力响应同时考虑了单元杆端位移产生的单元杆端力和单元上分布荷载产生的单元固端力。以香港青马悬索桥为例,分析了保留模态多模态耦合产生的动力效应、高频模态拟静力效应、单元上分布荷载产生的单元固端力及主缆上的抖振荷载等因素对主梁抖振内力响应的贡献。结果表明:保留模态多模态耦合产生的动力效应对主梁抖振内力响应占据主导地位,高频模态拟静力效应、单元上分布荷载产生的单元固端力等因素对主梁抖振内力响应均有一定的影响,主缆上的抖振荷载对主梁侧向抖振内力响应有较大贡献。     

Symmetric cavitation flow past a wedge in the presence of a source on the wedge or in the flow

A solution is found to the problem of symmetric cavitation flow over a wedge by an ideal incompressible fluid (in accordance with Efros's scheme [1]) in the presence of a point source in the flow or on the wedge. Expressions are obtained for the forces exerted on the source and the wedge by the fluid, the conditions under which there is a negative resistance (thrust) are indicated, and the profiles of the free streamlines are constructed for different values of the flow parameters.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Shidkosti i Gaza, No. 6, pp. 137–141, November–December, 1979.We thank L. I. Sedov for his interest in the work.     

基于首超破坏机制的大跨斜拉桥抖振动力可靠性分析

分别采用泊松分布和马尔可夫过程，给出了在一次强风作用下以及在设计基准期内桥梁结构某一特定截面或节点的抖振动力可靠性分析方法。然后，考虑斜拉桥的结构特点及其承受风荷栽的具体情况，确定了以斜拉桥的主梁系统为研究对象的结构体系抖振动力可靠性分析模型。在此基础上，采用串联失效模式，建立了斜拉桥主梁系统抖振动力可靠性分析过程。本文采用有限元法分析结构的空气静力响应。为了快速、准确地计算结构的抖振响应，考虑气弹力与抖振力的联合作用以及多模态耦合效应，采用有限元法和虚拟激励法相结合分析结构的抖振响应。最后，以某大跨斜拉桥为工程背景，对其主梁系统进行了基于刚度要求的抖振动力可靠性分析。     

Rheological studies of coal-oil mixtures

Summary Samples of stable coal-oil mixtures were prepared with coal concentrations ranging from 30–50% by weight. Extensive rheological data were obtained using capillary and cone-plate viscometers for samples of coal-oil mixtures and fuel-oil which served as a reference fluid. Viscosity measurements show coal-oil mixtures to be shear-thinning suspensions, i.e., the viscosity decreases moderately with increasing shear rates. In the concentration range of 30–40% coal, the coal-oil mixture shows a predominantly Newtonian behavior. For mixtures with coal concentrations higher than 40%, a yield point was observed. The study of these samples with the rotating-rod viscometer indicated a migration of coal particles away from the rotating rod with no noticeable rod climbing, thus no evidence of normal stress effects. The rheological data can be represented by any of the three two-parameter models: Power Law, Bingham Plastic, or Casson, with the last two models being more realistic and consistent with the observations.With 9 figures     

安装固定气动翼板的大跨桥梁抖振分析

建立了安装固定气动翼板的大跨桥梁多模态耦合抖振分析框架，推演了作用在整个桥梁-气动翼板系统上的抖振力和自激力的显式表达式，考虑了多模态耦合效应．基于有限元法，作用在主梁-气动翼板系统上的抖振力转化为节点力，进一步得到作用在整个桥梁上的抖振力并导出了其功率谱密度矩阵；作用在主梁．气动翼板系统上的气弹自激力转化为节点力，并将其表达为气弹刚度矩阵和气弹阻尼矩阵．通过组集得到系统的运动方程，然后运用虚拟激励法在频域计算系统的抖振响应．以某大跨斜拉桥为例进行研究，结果表明：在主梁下方安装-对固定气动翼板后，主梁的扭转角位移、角加速度以及侧向加速度响应能够得到有效控制。     

A FORM OF AERODYNAMIC ADMITTANCE FOR USE IN BRIDGE AEROELASTIC ANALYSIS

This paper returns to, and addresses, the question of identifying the nature of aerodynamic admittance in relation to extended-span bridges in wind. Theoretical formulations for the sectional aerodynamic forces acting upon the deck girder of a long-span bridge have conventionally been composed of the sum of two kinds of terms: aeroelastic terms and buffeting terms. The former employ frequency-dependent coefficients (“flutter derivatives”) associated with sinusoidal displacements of the structure, while the latter have typically been expressed in quasi-static terms with fixed lift, drag and moment coefficients. This inconsistency of formulation has required that at some point the buffeting terms, functions of gust velocity, be adjusted to a more compatible form through the introduction of the so-called aerodynamic admittance factors that are frequency-dependent. The present paper identifies a form of these several section-force factors as functions of the flutter derivatives themselves.     

Equations of hydromechanics and compression shock in two-velocity and two-temperature continuum with phase transformations

The equations of motion of multiphase mixtures have been considered in [1–10] and several other studies. In [1] it is proposed that the mixture motion be considered as an interpenetrating motion of several continua when velocity, pressure, mean density, concentration, etc., fields for each phase are introduced in the flowfield. The equations of motion are written separately for each phase, and the force effect of the other components is considered by introducing the interaction forces, which for the entire system are internal. The assumption of component barotropy is used to close the system.The energy equations are used in [2, 3] in place of the component barotropy assumption. Moreover, mixtures without phase transformations are considered. In [4] an analysis is made of the equations of turbulent motion with account for viscous forces for a two-velocity, but single-temperature medium in which equilibrium phase transformations are assumed, i. e., a two-phase medium is considered in which the phase temperatures are the same, the composition is equilibrium, but the phase velocities are different. In [5] the equations are written on the interface in a multicomponent medium consisting of barotropic fluids. A discontinuity classification is also presented here. In the aforementioned work [3] the equations on the shock are written for a continuum with particles without the use of the property of barotropy of the carrier fluid. Various different aspects of the motion of multiphase mixtures are considered in [6–11], for example, the effect of particle collisions with one another, the effect of the volume occupied by the particles on the parameters stream, shock waves, etc. In [7] a study is made of the force effect of an agitated medium on a particle on the basis of the Basset-Boussinesq-Oseen equation.In the following we derive the equations of motion of a two-velocity and two-temperature continuum with drops or particles with nonequilibrium phase transformations, i. e., a medium in which the phase velocities and temperatures are different and the composition may be nonequilibrium. In addition, we study the effect of the presence of particles or drops on the gas parameters behind a shock. Further, the equations obtained here are used to study compression waves, and in particular shock waves.The author wishes to thank Kh. A. Rakhmatulin, S. S. Grigoryan, and Yu. A. Buevich for helpful discussions and valuable comments.     

Flow of linear molecules through a 4:1:4 contraction–expansion using non-equilibrium molecular dynamics: Extensional rheology and pressure drop

In this work, non-equilibrium molecular dynamics simulations are used to generate the flow of linear polymer chains (monomer-springs with FENE potential) and a Lennard–Jones fluid (Newtonian fluid) through a contraction–expansion (4:1:4) geometry. An external force field simulating a constant pressure gradient upstream the contraction region induces the flow, where the confining action of the walls is represented by a Lennard–Jones potential. The equations of motion are solved through a multiple-step integration algorithm coupled to a Nosé-Hoover dynamics [S. Nose, A unified formulation of the constant temperature molecular dynamics methods, J. Chem. Phys. 81 (1984) 511–519], i.e., to simulate a thermostat, which maintains a constant temperature. In this investigation, we assume that the energy removed by the thermostat is related to the viscous dissipation along the contraction–expansion geometry. A non-linear increasing function between the pressure drop and the mean velocity along the contraction for the linear molecules is found, being an order of magnitude larger than that predicted for the Lennard–Jones fluid. The pressure drop of both systems (the linear molecules and Lennard–Jones fluid) is related to the dissipated energy at the contraction entry. The large deformation that the linear molecules experience and the evolution of the normal stress at the contraction entry follow a different trajectory in the relaxation process past the contraction, generating large hysteresis loops. The area enclosed by these cycles is related to the dissipated energy. Large shear stresses developed near the re-entrant corners as well as the vortex formation, dependent on the Deborah number, are also predicted at the exit of the contraction. To our knowledge, for the first time, the excessive pressure losses found in experimental contraction flows can be explained theoretically.     

Flow patterns and interfacial velocities near a moving contact line

Experimental data on velocity fields and flow patterns near a moving contact line is shown to be at variance with existing hydrodynamic theories. The discrepancy points to a new hydrodynamic paradox and suggests that the hydrodynamic approach may be incomplete and further parameters or forces affecting the surfaces may have to be included. A contact line is the line of intersection of three phases: (1) a solid, (2) a liquid, and (3) a fluid (liquid or gas) phase. A moving contact line develops when the contact line moves along the solid surface. A flat plate moved up and down, inside and out of a liquid pool defines a simple, reliable experimental model to characterize dynamic contact lines. Highlighted are three important conclusions from the experimental results that should be prominent in the development of new theoretical models for this flow. First, the velocity along the streamline configuring the liquid–fluid interface is remarkably constant within a distance of a couple of millimeters from the contact line. Second, the relative velocity of the liquid–fluid interface, defined as the ratio of the velocity along the interface to the velocity of the solid surface, is independent of the solid surface velocity. Third, the relative interface velocity is a function of the dynamic contact angle.     

Prediction of amount of entrained droplets in vertical annular two-phase flow

Prediction of amount of entrained droplets or entrainment fraction in annular two-phase flow is essential for the estimation of dryout condition and analysis of post dryout heat transfer in light water nuclear reactors and steam boilers. In this study, air–water and organic fluid (Freon-113) annular flow entrainment experiments have been carried out in 9.4 and 10.2 mm diameter test sections, respectively. Both the experiments covered three distinct pressure conditions and wide range of liquid and gas flow conditions. The organic fluid experiments simulated high pressure steam–water annular flow conditions. In each experiment, measurements of entrainment fraction, droplet entrainment rate and droplet deposition rate have been performed by using the liquid film extraction method. A simple, explicit and non-dimensional correlation developed by Sawant [Sawant, P.H., Ishii, M., Mori, M., 2008. Droplet entrainment correlation in vertical upward co-current annular two-phase flow. Nucl. Eng. Des. 238 (6), 1342–1352] for the prediction of entrainment fraction is further improved in this study in order to account for the existence of critical gas and liquid flow rates below which no entrainment is possible.Additionally, a new correlation is proposed for the estimation of minimum liquid film flow rate at the maximum entrainment fraction condition. The improved correlation successfully predicted the newly collected air–water and Freon-113 entrainment fraction data. Furthermore, the correlations satisfactorily compared with the air–water, helium–water and air–genklene experimental data measured by Willetts [Willetts, I.P., 1987. Non-aqueous annular two-phase flow. D.Phil. Thesis, University of Oxford]. However, comparison of the correlations with the steam–water data available in literature showed significant discrepancies. It is proposed that these discrepancies might have been caused due to the inadequacy of the liquid film extraction method used to measure the entrainment fraction or due to the change in mechanism of entrainment under high liquid flow conditions.     

An analysis of the chaotic motion of particles of different sizes in a gas fluidized bed

The dynamic behavior of individual particles during the mixing/segregation process of particle mixtures in a gas fluidized bed is analyzed. The analysis is based on the results generated from discrete particle simulation, with the focus on the trajectory of and forces acting on individual particles. Typical particles are selected representing three kinds of particle motion： a flotsam particle which is initially at the bottom part of the bed and finally fluidized at the top part of the bed; a jetsam particle which is initially at the top part of the bed and finally stays in the bottom de-fluidized layer of the bed; and a jetsam particle which is intermittently joining the top fluidized and bottom de-fluidized layers. The results show that the motion of a particle is chaotic at macroscopic or global scale, but can be well explained at a microscopic scale in terms of its interaction forces and contact conditions with other particles, particle-fluid interaction force, and local flow structure. They also highlight the need for establishing a suitable method to link the information generated and modeled at different time and length scales.     

Effect of capillary wave radiation on the oscillations of a vibrator

The oscillations of a rigid body on an elastic tie (vibrator) in an ideal incompressible fluid with a free boundary, on which surface tension forces act, are considered. The linearized problem of hydrodynamics is solved approximately in the self-consistent formulation, the reaction forces exerted on the body by the fluid are calculated, and an integrodifferential equation of motion is obtained. Using asymptotic methods, the average characteristics determining the damping coefficient and the frequency shift of the oscillations of the vibrator are obtained with allowance for the effect of the capillary waves radiated by the vibrator. Qualitative effects depending on the parameters of the system are revealed. The authors' numerical simulation of the motion of the vibrator completely confirms the qualitative conclusions concerning the nature of the oscillations of a body in a fluid having surface tension.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, pp. 126–132, March–April, 1995.     

Stability of a nonstationary round jet of an ideal incompressible fluid

The stability of transient flow in a cylinder of an ideal incompressible fluid with a free boundary is studied. There are 20 different cases of the behavior of small disturbances as a function of the parameters of the problem. In particular, if surface tension is not taken into account a round jet is stable with respect to axially symmetrical disturbances, but the introduction of capillary forces leads to a strong instability.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 4, pp. 80–84, July–August, 1972.In conclusion the author thanks V. V. Pukhnachev for formulation of the problem and valuable advice.     

Flow and heat transfer of a viscous fluid when there is a phase transition

A study is made of the problem of the flow and heat transfer of a fluid formed by the phase transition (melting or sublimation) when the end of a rod touches a heated surface. Problems of this kind arise, in particular, when a heated surface is cooled by means of the heats of the phase transitions of materials with an energy content. A solution is obtained to a simplified system of heat and mass transfer equations obtained by estimating the order of magnitude of the various terms in the Navier-Stokes equations in a manner similar to that in [1–3]. The parameters that govern the process are identified, and an approximate analytic solution is found for the quasi-stationary case. The analytic solution is compared with a numerical solution obtained iteratively.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 128–131, May–June, 1931.