Effect Of Lift Force Research Articles

Numerical study to predict the particle deposition under the influence of operating forces on a tilted surface in the turbulent flow

This study uses a v2-f turbulence model with a two-phase Eulerian approach. The v2-f model can accurately calculate the near wall fluctuations in y-direction, which mainly represent the anisotropic nature of turbulent flow. The model performance is examined by comparing the rate of particle deposition on a vertical surface with the experimental and numerical data in a turbulent channel flow available in the literature. The effects of lift, turbophoretic, electrostatic and Brownian forces together with turbulent diffusion are examined on the particle deposition rate. The influence of the tilt angle and surface roughness on the particle deposition rate were investigated. The results show that, using the v2-f model predicts the rate of deposition with reasonable accuracy. It is observed that in high relaxation time the effect of lift force on the particle deposition is very important. It is also indicated that decreasing the tilt angle from 90° to 0° enhances the deposition rate especially for large size particles. Furthermore, the results show that increasing the Reynolds number at a specific tilt angle decreases the rate of particle deposition and the tilt angle has insignificant impact on the particle deposition rate in high shear velocity or high Reynolds number.

Deposition of aerosol in a laminar pipe flow

In a laminar pipe flow, thermophoretic deposition occurs when the temperature of the pipe wall is less than the temperature of the fluid. For a horizontal pipe, gravity has a significant effect on the deposition of aerosol. Due to the laminar flow of gas fluid, a lift force is imposed on the particle and could affect the deposition of aerosol. In the present work, we considered the influences of various factors on the deposition of aerosol, including diffusion and convection, thermophoresis, gravitational settling and the lift force effect. The revised semi-implicit method for pressure-linked (SIMPLER) was employed to solve the aerosol transport equation. The deposition efficiency of aerosol in a pipe was obtained and the concentration distribution of aerosol at an arbitrary cross-section of pipe was given. The results reveal that when gravitational settling was considered the deposition efficiency had a minimum, corresponding to the penetration efficiency having a maximum. For large particles, the deposition of aerosol was dominated by external forces, and the critical particle trajectory method (CPTM) was used to analyze the deposition of aerosol with the action of thermophoretic force and gravity. The result from CPTM coincided very well with the result from SIMPLER.

State sensitivity analysis of the pantograph system for a high-speed rail vehicle considering span length and static uplift force

In this paper, dynamic characteristics analysis of catenary and pantograph systems for a high-speed rail vehicle is carried out. The catenary system is considered to be a beam model. The analysis of the catenary based on the finite element method (FEM) is performed to develop the pantograph. The stiffness value can be obtained at each nodal point on the contact wire. State sensitivity analysis was executed with respect to design variables considered by the pantograph system. The pantograph of linear spring–mass–damper system is considered as a 3dof model using lumped parameters. Dynamic modeling of the pantograph system is verified by actual experimental vibration data. To perform the sensitivity analysis, our study was considered lift force effect of the pan-head occurring at high-speed runs. Also, a span length and static uplift force were included into design variables. As a result, we could confirm that span length and plunger spring constant are some of the important design variables of catenary and the pantograph systems.

Quasi-direct numerical simulation of lift force-induced particle separation in a curved microchannel by use of a macroscopic particle model

The macroscopic particle model (MPM) based on the finite volume method is employed to validate a mechanism of lift force-induced particle separation in a curved microchannel. According to the particle velocity at each time step in the unsteady simulation, the MPM gives momentum to those fluid cells touching the particle physical boundary. The summation of the given momentum with the reversed sign is divided by the time step to obtain the hydrodynamic force acting on the particle. Namely, the existence and motion of the particle causes fluid flow around the particle, while the flow field caused by the particle determines the particle motion by means of the hydrodynamic force. Therefore, the MPM can be regarded as implementing a quasi-direct numerical simulation over the static computational cells. The lift force acting on a spherical particle in a shear flow is a purely hydrodynamic force caused by the flow field around the particle. It is expected, therefore, that the MPM could predict the lift force effect without any additional model. At first, it is shown that the MPM is capable of predicting particle migration away from the wall of a straight microchannel due to the lift force. In a curved microchannel, subsequently, the particle trajectories from representative release points predicted by the MPM are compared to those predicted by a common particle tracking method without any lift force model. The MPM predicted that the particle trajectories are confined in the outer region of the channel cross-section. On the other hand, the circulating trajectories predicted by the tracking method tend to expand due to centrifugal force caused by the Dean vortices. It is concluded, therefore, that the lift force due to the steep shear rate is a significant factor to cause particle separation in a curved microchannel.

A dispersion force approach to modelling the effect of lift forces on fibre dispersion

Wood fibres suspended in air were studied whilst flowing through a throttle. Measurements of volume fraction and velocity were compared with results from a two-fluid model simulation. Results from earlier work have shown that the lift forces acting on the individual fibres are of importance for the dispersion of volume fraction. Since the orientation of the individual fibres cannot be determined, a dispersion force was utilised to model the dispersing effect of the lift forces. The addition of a lift dispersion model significantly improved the agreement between measurement and model data.

Eulerian–Lagrangian simulations of unsteady gas–liquid flows in bubble columns

We studied the dynamics of gas–liquid flows in a rectangular bubble column using Eulerian–Lagrangian simulations. Three-dimensional, unsteady simulations were performed to simulate the dynamic characteristics of the oscillating bubble plume. The effect of superficial gas velocity and aerated liquid height-to-column width ( H/ W) ratio on the dynamic and time-averaged flow properties was studied and the simulated results were validated using wall pressure and voidage fluctuation measurements. The effect of lift force and numerical diffusion on the dynamic and time-averaged properties is discussed in detail. Further, the results obtained using the Eulerian–Lagrangian simulations were compared with the Eulerian–Eulerian simulations. The bubble scale information, which is otherwise lost in the Eulerian–Eulerian simulations, was validated using the voidage fluctuation measurements. Such experimentally validated Eulerian–Lagrangian models will be useful for the simulation of mass transfer and reactions in bubble columns.

Turbulent bubbly flow

The effect of bubbles on fully developed turbulent flow is investigated numerically and experimentally, summarizing the results of our previous papers (Mazzitelli et al., 2003, Physics of Fluids 15, L5. and Journal of Fluid Mechanics 488, 283; Rensen, J. et al. 2005, Journal of Fluid Mechanics 538, 153). On the numerical side, we simulate Navier–Stokes turbulence with a Taylor–Reynolds number of Re λ≈60, a large large-scale forcing, and periodic boundary conditions. The point-like bubbles follow their Lagrangian paths and act as point forces on the flow. As a consequence, the spectral slope is less steep as compared to the Kolmogorov case. The slope decrease is identified as a lift force effect. On the experimental side, we do hot-film anemometry in a turbulent water channel with Re λ ≈ 200 in which we have injected small bubbles up to a volume percentage of 3%. Here the challenge is to disentangle the bubble spikes from the hot-film velocity signal. To achieve this goal, we have developed a pattern recognition scheme. Furthermore, we injected microbubbles up to a volume percentage of 0.3%. Both in the counter flowing situation with small bubbles and in the co-flow situation with microbubbles, we obtain a less spectral slope, in agreement with the numerical result.

Vertical Dispersion of Fine and Coarse Sediments in Turbulent Open-Channel Flows

Through using a kinetic model for particles in turbulent solid–liquid flows, underlying mechanisms of sediment vertical dispersion as well as sediment diffusion coefficient are investigated. Four hydrodynamic mechanisms, namely gravitational settling, turbulent diffusion, effect of lift force, and that of sediment stress gradient, coexist in two-dimensional (2D) uniform and steady open-channel flows. The sediment diffusion coefficient consists of two independent components: one accounts for the advective transport of sediment probability density distribution function due to sediment velocity fluctuations, and the other results from sediment–eddy interactions. Predictions of the kinetic model are in good agreement with experimental data of 2D open-channel flows. In such flows, it is shown that: (1) the parameter γ (i.e., the inverse of the turbulent Schmidt number) may be greater than unity and increases toward the bed, being close to unity for fine sediments and considerably large for coarse ones; (2) effects of lift force and sediment stress gradient become significant and need to be considered below the 0.1 flow depth; and (3) large errors may arise from the traditional advection–diffusion equation when it is applied to flows with coarse sediments and/or high concentrations.

Dynamics of suspended particles in eccentrically rotating flows

The motion of a light particle in an eccentrically rotating cylinder provides a method for verifying stationary history lift force effects at low but non-zero particle Reynolds numbers. We examine the flow in detail using a Lagrangian equation of motion for constant, non-zero-vorticity flows, and we predict a measurable and stationary contribution of history lift effects that can be verified experimentally with current experimental techniques. Because the history lift contribution is relevant only under certain conditions (which are determined in this work), the present flow configuration also allows one to isolate history drag effects under normal gravitation conditions without resorting to the tethered-particle arrangement used in previous works. We formulate and solve the trajectory problem for light particles that attain stable orbital motion, and we propose an experimental concept that makes possible the study of individual contributions of Lagrangian forces to the motion of small particles in viscous flows.

Mechanisms of particle vertical diffusion in sediment-laden flows

Diffusion coefficient of natural sediments and effects of lift force and gradient in particle velocity fluctuations were investigated through using a closed kinetic model. Comparison against experimental data of Einstein & Chien (1955) validated the model. The diffusion coefficient eyy of medium and large sediments distinctly exceeds fluid eddy viscosityv f t , while eyy of fine sediments approximately equalsv f t . In the measured region of0.03<y/H<0.4, e yy/v f t increases with the distance from the wall decreasing. Combined effects of lift force and gradient in particle velocity fluctuations change sediment gravitational settling remarkably belowy/H=0.2, and need to be accounted for describing sediment diffusion in this region.

Numerical study of the lift force influence on two-phase shock tube boundary layer characteristics

The importance of the lift force acting on the dispersed phase in the boundary layer of a laminar gas-particle dilute mixture flow generated by a shock wave is investigated numerically. The particle phase is supposed to form a continuum and is described by an Eulerian approach. The ability of the Eulerian model to simulate particle flows and the importance of the two-way coupling are proven by comparison with experimental data as well as with the numerical results from schemes based on a Lagrangian approach. The models used for the lift force are discussed through comparisons between numerical and experimental results found in the literature. Some results about the formation of a dust cloud are numerically reproduced and show the major role of the lift force. Simulations of two-dimensional two-phase shock tube flows are also performed including the lift force effects. Although the wave propagation is weakly influenced by the lift force, the force modifies substantially the dynamics of the flow near the wall.

Mathematical Modeling of Iron and Steel Making Processes. Evaluation of Multiphase Phenomena in Mold Pool under In-mold Electromagnetic Stirring in Steel Continuous Casting.

Multiphase phenomena in the application of in-mold electromagnetic stirring in continuous casting were discussed through cold experiment using mercury and numerical simulation by using two fluid model. The result revealed the critical flow rate of argon injected in the submerged entry nozzle, which leads to the change in flow pattern in the bulk liquid metal inside the mold pool. This change does not have a large effect on the flow driven by in-mold electromagnetic stirring because the Lorentz force acts mainly in the vicinity of solidifying shell except for the case of large amount of the argon flow rate. The particle behavior under in-mold electromagnetic stirring in the vicinity of the solidifying shell was also discussed by solving near-wall fluid flow and employing the particle tracking method, which showed the important effect of lift force by the increase in velocity inclination near the solidifying shell by electromagnetic field.

Study of magnetic particles pulse-injected into an annular SPLITT-like channel inside a quadrupole magnetic field

Advantages of the continuous magnetic flow sorting for biomedical applications over current, batch-wise magnetic separations include high throughput and a potential for scale-up operations. A continuous magnetic sorting process has been developed based on the quadrupole magnetic field centered on an annular flow channel. The performance of the sorter has been described using the conceptual framework of split-flow thin (SPLITT) fractionation, a derivative of field-flow fractionation (FFF). To eliminate the variability inherent in working with a heterogenous cell population, we developed a set of monodisperse magnetic microspheres of a characteristic magnetization, and a magnetophoretic mobility, similar to those of the cells labeled with a magnetic colloid. The theory of the magnetic sorting process has been tested by injecting a suspension of the magnetic beads into the carrier fluid flowing through the sorter and by comparing the theoretical and experimental recovery versus total flow-rate profiles. The position of the recovery maxima along the total flow-rate axis was a function of the average bead magnetophoretic mobility and the magnetic field intensity. The theory has correctly predicted the position of the peak maxima on the total flow-rate axis and the dependence on the bead mobility and the field intensity, but has not correctly predicted the peak heights. The differences between the calculated and the measured peak heights were a function of the total flow-rate through the system, indicating a fluid-mechanical origin of the deviations from the theory (such as expected of the lift force effects in the system). The well-controlled elution studies using the monodisperse magnetic beads, and the SPLITT theory, provided us with a firm basis for the future sorter evaluation using cell mixtures.

Motions of small particles in a turbulent simple shear flow field under microgravity condition

Motions of small rigid spheres in a turbulent flow field in the presence of a uniform mean shear and in the absence of gravitational effect are studied. The particle equation of motion, which includes the Stokes drag and the Saffman lift force effects, is treated as a stochastic differential equation. The spectral method is used and analytical expressions relating the components of particle response statistics to that of the flow field are developed. The particle spectral intensities, autocorrelation functions, and mean-square velocities, as well as particle diffusivities for different particle relaxation times and mean shear rates are evaluated. It is shown that the presence of a mean shear field enhances the particle diffusivity in the transverse direction. Experimental observations of particle mass diffusivity greater than that of the fluid particle may then be explained by this shear induced enhancement.

Vertical dispersion of spherical, heavy particles in turbulent open channel flow

The results of an experimental study on the motion of heavy particles (heavierthan water) in an open channel flow over a smooth bed are presented in the paper. Some aspects of the diffusion and dispersion of the particles are analysed and especially the effects of lift force and the quadratic nature of drag forces when present. The results show that for a given fall velocity in still water, the vertical dispersion increases with increase in particle diameter. Measured mean particle downward velocities are lower than the settling velocities in still water.

Lift forces on suspended sediment particles in laminar flow; experiments and sedimentological interpretation

ABSTRACT A sphere carried by laminar flow past a planar boundary experiences a force away from the boundary. The sedimentological implications of this effect, both for transportation of coarse sediment in strong turbu'ent flows and for deposition of fine sediments from oceanic bottom currents, were explored by estimating the lift force on small, nearly neutrally buoyant spheres suspended in laminar flow in a laboratory flume and evaluating how closely this models the lift force in the natural flows. The results suggest that this lift-force effect is not important in natural sedimentary processes.

531. Desorption of hydrogen from platinum catalyst: Y Kubokawaet al, J Phys Chem, 68, May 1964, 1244–1245

Flashing of initially sub-cooled water in a vertical circular converging-diverging nozzle is simulated with two-fluid model incorporating drag and non-drag forces. Phase change is assumed to be induced only by interphase heat transfer while pressure jump across the interface is ignored. The reliability of CFD simulations is confirmed by comparison with experimental data and one-dimensional results basing on a drift-flux model. Satisfactory prediction of mass flow rate and cross-section averaged parameters is achieved. The predicted radial distribution of void fraction is however much more flat than the measured one. The discrepancy is found to be caused by the effect of lift force and the reversal of relative velocity. Cases characterised with large pressure-undershoot exhibit significant pressure non-equilibrium effect in form of a pressure recovery process. Sensitivity tests on bubble number density, heat transfer coefficient as well as nucleation are performed.