Shear-induced Lift Research Articles

On the shear-induced lift in two-way coupled turbulent channel flow laden with heavy particles

The importance of shear-induced lift, i.e. Saffman lift, is investigated in two-way coupling point-particle direct numerical simulation of turbulent channel flow laden with heavy particles. A new criterion is established for the critical particle diameter normalized by wall viscous length, and the effect of Saffman lift on particle motion can be neglected when the particle diameter is smaller than the critical value. The new criterion agrees well with the numerical results. We further study the influence of Saffman lift on particle motion and turbulence modulation. The results suggest that the Saffman lift will increase near-wall particle velocity and reduce particle accumulation therein. By integrating the particle motion equation, it is demonstrated that the mean particle streamwise velocity is dependent on the particle wall-normal velocity. This theoretically explains why the presence of a wall-normal force alters the streamwise velocity of particles. A theoretical profile of mean particle streamwise velocity at different Stokes numbers is then obtained by introducing the diffusive gradient hypothesis and Prandtl mixing length model. In addition, the present results reveal that the Saffman lift tends to augment the level of turbulence attenuation. The spectral analysis shows that the Saffman lift reduces the turbulent energy of small scales in the buffer region and large structures in the logarithmic region. When the Saffman lift is absent, near-wall particle streaks can be observed in the buffer region, which tend to separate fluid streaks. By contrast, the Saffman lift tends to prevent the formation of near-wall particle streaks.

Experimental investigation on dynamic characteristics of single bubble near wall in shear flow

The bubble near the wall of shear flow will be subjected to both wall-induced lift and shear-induced lift. The two-lift interaction will markedly change the dynamic behavior of the bubble. In this experiment, the lateral motion of a single bubble (deq=2.33−3.42 mm, Reb=470−680) rising near the vertical wall in a linear shear flow was studied. The positive-synergy and negative-synergy between the wall- and shear-induced lift effects on bubble dynamics were compared. The experiment was carried out in a vertical water tunnel with a curved screen used to generate a stable linear shear flow. Using the shadow method and two charge-coupled device cameras, the movement parameters of the bubble were captured, including the movement trajectory of the bubble, length–diameter ratio, and instantaneous velocity. The lift coefficient CL and drag coefficient CD were obtained by quasi-steady-state analysis and calculation. By fitting the steady lift coefficient, the relation of CL with dimensionless wall distance S* and the Reynolds number Reb was obtained. The results show that there is a critical value of the initial dimensionless distance S* about [S*] = 1.6. When S* > [S*], the bubble is subjected to both wall-induced lift and shear-induced lift. The lift coefficient CL decreases with the increase in S*. When S* < [S*], the bubble receives additional induced lift from the wall. The CL of the smaller bubble was smaller and increases with the increase in S*, while the deformation of the larger bubble will interact with the wall to produce deformation lift away from the wall, presenting larger CL, and decrease with the increase in S*.

Self-ordering and organization of a staggered oblate particle pair in three-dimensional square ducts

We numerically investigate the formation and ordering of staggered oblate particle pairs in three-dimensional straight ducts with a square cross section. The lattice Boltzmann method is employed to simulate rigid particle pairs in a Newtonian liquid. The effects of initial axial spacing, Reynolds number, blockage ratio, and particle aspect ratio on the formation process, migration behavior, and interparticle spacing are explored in detail. Current results indicate that the process from initial to final steady state can be divided into two stages. The first stage is rapid migration from initial positions toward equilibrium positions under shear-induced lift force and wall-induced repulsive force. The second stage is the slow self-assembly of stable particle pairs in the axial direction due to the interparticle interaction. Interestingly, initial axial spacing significantly affects the formation process of particle pairs but does not affect the final steady state. It is found that the equilibrium positions of staggered particle pairs move slightly toward the duct walls, and the axial spacing increases with increasing Reynolds number or particle aspect ratio, or decreasing blockage ratio. For a staggered particle pair, the second particle will occupy the eddy center induced by the first focusing particle. Based on the existing data, a correlation is put forward to predict the axial interparticle spacing of staggered oblate particle pairs in duct flows. The present results may give insights into manipulating and comprehending non-spherical particle dynamics in microfluidic applications.

Application of the Euler–Lagrange Approach and Immersed Boundary Method to Investigate the Behavior of Rigid Particles in a Confined Flow

The presence of particles with a small but finite size, suspended in viscous fluids with low volumetric concentrations, is observed in many applications. The present study focuses on the tridimensional and incompressible lid-driven flow of Newtonian fluids through the application of the immersed boundary method and the Euler–Lagrange approach. These methods are used to numerically predict three-dimensional particle motion by considering nearly neutrally buoyant conditions as well as all relevant elementary processes (drag and lift forces, particle rotation, particle–wall interactions, and coupling between phases). Considering the current stage of the numerical platform, two coupling approaches between phases are considered: one-way and two-way coupling. A single particle is inserted in the cavity after steady-state conditions are achieved. Its three-dimensional motion is obtained from numerical simulations and compared with research data, considering the same conditions, evidently showing that the particle trajectory follows the experimental data until the first collision with a solid surface. After this first contact, there is a deviation between the results, with the two-way coupling results better representing the experimental data than the one-way coupling results. The dimensionless forces’ peaks acting on the particles are associated with the relative velocity of the particle near the wall–particle collision position. In terms of magnitude, in general, the drag force has shown greater influence on the particle’s motion, followed by the rotation-induced and shear-induced lift forces. Finally, a special application is presented, in which 4225 particles are released into the domain and their dynamic is evaluated throughout dimensionless time, showing similar behavior for both couplings between phases, with variations in local concentrations observed in certain regions. The mean square displacement used to quantify the dispersion evolution of the particles showed that the particulate flow reaches an approximately homogeneous distribution from the moment of dimensionless time tU/S = 130.

Numerical study of bacteria removal from microalgae solution using an asymmetric contraction-expansion microfluidic device: A parametric analysis approach

Microalgae have been remarkably taken into account due to their wide applications in the biopharmaceutical, nutraceutical and bio-energy fields. However, contamination of microalgae with bacteria still appears to be a concern, adversely impacting products’ quality and process efficiency. Microalgae decontamination with conventional techniques is usually expensive and time-consuming. Moreover, damage to microalgae cells is highly possible. Asymmetric contraction-expansion microchannels (Asym-CEMCs) are promising passive microfluidic devices that can overcome conventional techniques' drawbacks with their standing-out features. However, the flexibility of Asym-CEMCs performance arising from their various tunable geometrical parameters results in the fact that their performance for separating a target particle cannot be predicted without an investigation. In this work, for the first time, Asym-CEMCs were numerically studied for the removal of a very conventional bacteria, B. subtilis (1 μm), from one of the most popular microalgae, C. vulgaris (5.7 μm). The influences of the microchannel aspect ratio, length and width ratios of the expansion-to-contraction zones, and the total flow rate on the separation resolution and focusing width of the particles were investigated by a 3D numerical model. The aspect ratio had the strongest influence on the Asym-CEMC performance, however, the length ratio had no considerable effect on the results. A decrease in the aspect ratio augmented the shear-induced lift force and Dean drag force, leading to a significant separation resolution improvement. Microalgae decontamination was also enhanced by an increase in the total flow rate and expansion-to-contraction width ratio. Finally, a locally optimized Asym-CEMC with an aspect ratio of one and expansion-to-contraction width and length ratios of 4.7 and 2.07, respectively, was proposed, leading to complete microalgae decontamination with a high normalized separation resolution of 0.6. In a word, Asym-CEMCs with tailored dimensions are promising for successfully decontaminating microalgae from bacteria.

Study of red blood cells and particles in stenosed microvessels using coupled discrete and continuous forcing immersed boundary methods

A computational study of the blood flow in a stenosed microvessel is presented using coupled discrete ghost-cell and continuous-forcing immersed boundary methods. This study focuses on studying platelet behaviors near the stenosis with deformable red blood cells (RBCs). The influence of varying hematocrit, area blockage, stenosis shape, and driving force on flow characteristics, RBCs, and particle behaviors is considered. Distinct flow characteristics are observed in stenosed microvessels in the presence of RBCs. The motion of RBCs is the major cause of time-dependent oscillations in flow rates, while the contribution of particles to the fluctuations is negligible. However, this effect decreases when the stenosis is elongated in the axial direction. Interestingly, as the hematocrit level increases, downstream particles move closer to the vessel wall due to the enhanced shear-induced lift force resulting from the interaction among RBCs and particles. Furthermore, it is observed that geometrical changes in the stenosis have a more significant impact on the axial profile of particle concentration compared to changes in hematocrit or driving force. An asymmetric stenosis leads to asymmetric profiles in the flow velocity and the distribution of cells and particles due to the geometric focusing effect of the stenosis. There is no significant change in flow rates until a blockage of 0%–50%, but a sudden increase in the root mean square of flow rates occurs at an 80% blockage. This study contributes to our understanding of the rheological behaviors of RBCs and rigid particles in a stenosed microvessel under various hemodynamic conditions.

Shear induced lift and rotation on MicroFiber deposition in low Reynolds number flows

Lateral migration is of significant importance to fiber deposition in wall-bounded flows, especially when other active external physical transport mechanisms are absent. Due to great technical difficulty, investigation on this phenomenon is limited to fundamental derivations, and the implication to particle deposition has not been fully explored. To fill the gap, this study investigated the shear-induced lift and rotation on microfiber transport and deposition in low Reynolds number flows. Transport and deposition of non-neutrally buoyant ellipsoidal fibers in Poiseuille flow in horizontal and vertical channels is systematically examined, and various lateral migration scenarios are carefully investigated. It was found out that, in absence of the sideway gravity, shear-induced lift and rotation cause the fibers to drift across main streamlines in the vertical channel. This lateral movement is either the driving force for fiber deposition in a downward flow or pushes the particles toward channel center in an upward flow configuration. Lateral migration velocity in the vertical channel is found to correlate positively with fiber length and shear rate. Lateral migration is negligible in a horizontal channel where the sideway gravity is dominant. Current study clearly identified the presence of fiber transport scenarios where lateral migration driven by the shear-induced lift and rotation is the major contributor for fiber deposition in wall-bounded flows. The finding is of particular significance to practical applications, as frequently, they involve a combination of these transport scenarios either actively or passively. The study also provided additional insights to examine the equivalency of spheres to fiber dynamics.

Trajectory of a spherical bubble rising in a fully developed laminar flow

The rising trajectory of bubbles subjected to shear-induced lift force in a vertical channel is of great interest for designing and optimising a variety of electrochemical equipment. In this work, the rising trajectory of a spherical microbubble with a diameter of 0.3-1.0mm in a vertical channel with a fully developed laminar flow is investigated experimentally. Subsequently, the lift and drag forces on the bubble are assessed. Due to the limitation of the existing correlations for lift force coefficient, a new correlation is developed, which can be used to estimate the trajectory of a bubble in a vertical channel. The effect of flow velocity gradient and bubble diameter on the bubble motion is discussed to control bubble rising trajectory. It is concluded that the lift coefficient for a spherical microbubble in vertical channels with a fully developed laminar flow is slightly higher than the reported shear lift coefficient for larger bubbles rising in a high viscous liquid.

Combined three-dimensional flow field measurements and motion tracking of freely moving spheres in a turbulent boundary layer

A combination of time-resolved tomographic particle image velocimetry, refractive index matching technique and machine vision algorithms was used to measure the translational and rotational motion of freely moving, nearly neutrally buoyant spheres in a fully developed turbulent boundary layer (TBL). Located in the buffer and logarithmic layers, the hydrogel spheres ( $\sim$ 70 inner wall units in diameter) were refractive index matched with the water and tagged by ‘spokes’. Besides translational motion, the spheres exhibited significant rotation. The spheres were surrounded by typical coherent structures observed in TBLs, among them hairpin packets and transverse and longitudinal vortices that induced ejections and sweeps. While the majority of instantaneous sphere Reynolds numbers did not exceed 100, and vortex shedding was not observed, the results showed that the spheres may affect the evolution of hairpin packets in TBLs due to their finite size. The instantaneous rotation-, wall- and shear-induced lift forces, as well as the drag forces, acting on the spheres were estimated using available correlations for the lift and drag coefficients. Results hinted at negative shear-induced lift due to flow separation at a smaller critical Reynolds number than incorporated in the correlations that do not include the effect of ambient turbulence. The results indicated further that the drag force aided by the rotation-induced lift force was instrumental in keeping one of the spheres aloft. For the wall-ward moving spheres, lift forces opposed sphere motion. As a result, the spheres approached the wall with velocities lower than their quiescent settling velocity.

Improved modeling of wall effects on interfacial momentum exchange for wall-bounded bubbly flows based on resolved simulations

A two-fluid model based on an Eulerian-Eulerian approach must accurately model interfacial momentum exchange, which includes drag force and shear-induced and wall-induced lift forces. However, the modelling of the wall effect is not yet fully established. Therefore, we propose a new two-fluid closure model for wall effect on drag and lift forces in bubbly flows. The present model is based on resolved simulations of flow over a spherical bubble moving near the wall and fitted correlations for simulated drag and lift coefficients. In the present wall force model, the effect of the bubble Reynolds number is included explicitly in the two-fluid model framework. To validate the present model, numerical simulations are conducted for both laminar and turbulent bubbly flows. As a result, more accurate and reliable results for bubbly flows could be produced by using the present wall model in combination with the shear-induced lift in Tomiyama et al. (2002).

Influence of surfactant contaminations on the lift force of ellipsoidal bubbles in water

The shear-induced lift force is known to influence the lateral distribution of gas bubbles in bubbly flows. Although the hydrodynamic behavior of a bubble can be greatly affected by surfactants that are present in the liquid bulk, their influence on the lift force has only been investigated to a limited extent. In our previous work we investigated the influence of impurities on the lift force in air-water flows and could reveal non-negligible changes even without a modification of the bubble drag or shape. To bring further insight on changes caused by higher surfactant concentrations, the lift coefficient of single ellipsoidal bubbles of different sizes, which rise in water with varying degree of contamination are experimentally determined in this work. For this purpose, different amounts of 1-Pentanol as well as Triton X-100 were added to the flow. The results reveal a strong dependency of the lift coefficient on the bubble shape, where different findings in the literature for bubbles with lower Reynolds numbers could also be observed for ellipsoidal bubbles in water.

Utilization of direct forcing immersed boundary methods for the optimization of inertial focusing microfluidics

Inertial focusing microfluidics have gained significant momentum in the last decade for their ability to separate and filter mixtures of particles and cells based on size [1-3]. However, the most important feature is that the separation is passive, without the need for external forces. At the heart of inertial focusing is the balance between counteracting lift forces: shear and wallinduced lift. Shear-induced lift is a product of the curvature of the fluid flow and the rotation of the particle in the flow, while wall-induced lift is generated by the disturbance of the fluid by the particle near a wall. This phenomenon was first observed by Segre and Silberberg for the focusing of particles in a pipe, and was later extended to the focusing of cells and particle in rectangular channels [4]. Taking advantage of inertial focusing we explore particle capture utilizing an expanded channel microfluidics chip design. By expanding a small region of the straight channel microvortices form in the well, which allows for size selective trapping of particles.

Transport of large particles through the transition to turbulence of a swirling flow

In inhomogeneous turbulent flows particles whose size are close to the flow integral length scale do not sample the flow homogeneously. Instead they explore preferentially regions of low velocity fluctuations. We study how this preferential sampling becomes more and more accentuated when the flow fluctuations decrease as the Reynolds number is lowered. In the absence of fluctuations, the large particles are trapped in the vicinity of the islands of the laminar flow, due to a shear-induced lift force, for times several order of magnitude longer than those associated with the flow forcing.

Wake-induced lateral migration of approaching bubbles

In the motion of two gravity-driven bubbles arranged in a line, the trailing bubble is known to accelerate in the wake of the leading bubble. Furthermore, the approaching bubble migrates laterally as a result of bubble–bubble interactions. This paper presents the physical mechanisms for the acceleration and lateral motions of deformable bubbles under stable conditions, i.e., rectilinear motion in a solitary bubble, using numerical simulations. First, the trailing bubble decreases the drag coefficient relative to the case of a spherical bubble as a result of the increased vorticity generated at the leading bubble surface by its deformation. Second, the trailing bubble moves laterally as a result of the shear-induced lift force. In addition, lift reversal occurs in high Bond number cases and very weak lift occurs in low Galilei number cases. Predictions under the assumption of spherical bubbles nearly reproduce the interaction of a pair of deformable bubbles; however, the motion associated with the lift reversal cannot be predicted. Third, the bubbles repel each other as a result of their potential interaction when they are adjacent. This repulsive interaction is due to both the pressure at the surface and the vortex interaction around the bubbles.

Particle–fluid–wall interaction of inertial spherical particles in a turbulent boundary layer

Abstract

Nonlinear dynamics of inertial particles in the ocean: from drifters and floats to marine debris and Sargassum

Buoyant, finite-size or inertial particle motion is fundamentally unlike neutrally buoyant, infinitesimally small or Lagrangian particle motion. The de-jure fluid mechanics framework for the description of inertial particle dynamics is provided by the Maxey-Riley equation. Derived from first principles - a result of over a century of research since the pioneering work by Sir George Stokes - the Maxey-Riley equation is a Newton-type-law with several forces including (mainly) flow, added mass, shear-induced lift, and drag forces. In this paper we present an overview of recent efforts to port the Maxey-Riley framework to oceanography. These involved: 1) including the Coriolis force, which was found to explain behavior of submerged floats near mesoscale eddies; 2) accounting for the combined effects of ocean current and wind drag on inertial particles floating at the air-sea interface, which helped understand the formation of great garbage patches and the role of anticyclonic eddies as plastic debris traps; and 3) incorporating elastic forces, which are needed to simulate the drift of pelagic Sargassum. Insight on the nonlinear dynamics of inertial particles in every case was possible to be achieved by investigating long-time asymptotic behavior in the various Maxey-Riley equation forms, which represent singular perturbation problems involving slow and fast variables.

Shear-induced lift force on spheres in a viscous linear shear flow at finite volume fractions

Several studies have shown a significant increase in drag on a distribution of solid spherical particles within a fluid with increasing particle volume fraction. As a result, many empirical drag laws accounting for the dependence on the Reynolds number and volume fraction can be found in the literature. This study investigates the possibility of a similar effect of the particle volume fraction on the mean hydrodynamic lift force on randomly distributed spherical particles in a linear shear flow. Particle-resolved direct numerical simulations are performed to evaluate the mean lift force, and the results are compared with the case of an isolated particle in a linear shear flow for the same Reynolds number and shear rate. The mean lift force acting on the particles appears to remain nearly the same as that on an isolated particle. However, due to the influence of neighboring particles, there is a substantial force variation in transverse directions on each individual particle, whose magnitude is comparable to the mean drag force. The distribution of drag force in a linear shear flow is shown to be nearly the same as in a uniform flow at the same volume fraction and Reynolds number. A simple stochastic model based on a Gaussian distribution is presented for the lift force variation, and its performance is compared to the prediction of the deterministic pairwise interaction extended point-particle model.

Prediction of particles deposition in a dilute quasi-steady gravity current by Lagrangian markers: effect of shear-induced lift force

A gravity current in a channel at the presence of a triangular obstacle was investigated using LES simulation and the Eulerian approach. The Saffman–Mei equation was also applied to examine the effect of shear-induced lift force on particle deposition. To this end, particles were considered as Lagrangian markers and injected into gravity current. It is important to keep in mind that the interaction between the gravity current and particles was treated as a one-way coupling. The results show that shear-induced lift force prevents particles to deposit at the entrance of channel, where the velocity gradient is high. Furthermore, a reduction in the rate of sediment deposition can be seen again in the vicinity of obstacle due to high velocity gradient. The important result is that the shear-induced lift force has an important role in the cases with considerable velocity gradient in quasi-steady flows and this force can affect the pattern of sedimentation over time. Q criterion is utilized to depict the vortical structures of flow. Vortical structures with larger diameter, that indicate stronger vortexes, has been seen in various sections of channel, especially in the region near the obstacle due to the presence of obstacle.

Towards a unified shear-induced lift model for prolate spheroidal particles moving in arbitrary non-uniform flow

The paper proposes a unified shear-induced lift force model which divides the lift force into four lift components arising from the spin tensor, the volumetric and the deviatoric parts of the rate of deformation tensor, and the inertia effect of the Stokes drag. This unified model is successfully simplified into a shear-induced lift model for prolate spheroidal particles moving in arbitrary flow conditions via analogy arguments. The simplified shear-induced lift model for prolate spheroidal particles is verified by comparing it with several established lift force models via simulation of a prolate spheroidal particle moving in the Poiseuille and lid-driven cavity flows. The computational results demonstrate that the present lift force model for prolate spheroidal particles is applicable in flow cases with streamwise and non-streamwise flow shear. The implementation of the simplified lift model leads to computational results with reasonably small difference to the results of the full lift model of Cui et al. [Int. J. Multiph. Flow, 111, 232–240 (2019)], with a significantly decreased computational cost, rendering it as suitable for the implementation in large scale Lagrangian particle tracking.

Electrophoretic slip-tuned particle migration in microchannel viscoelastic fluid flows

Particles migrate towards the center or walls of a rectangular microchannel if they lead or lag a viscoelastic fluid flow due to positive and negative electrophoresis, respectively. This is opposite to a Newtonian fluid. We attribute this to the shear-induced extra lift in a viscoelastic fluid.