Suspension Flow Research Articles

Ergodic optimization restricted on certain subsets of invariant measures

In this article, we pay attention to transitive dynamical systems having the shadowing property and the entropy functions are upper semi-continuous. As for these dynamical systems, when we consider ergodic optimization restricted on the subset of invariant measures whose metric entropy are equal to or greater than a given constant, we prove that for C0-generic real continuous functions, the ergodic optimization measure is unique, ergodic, has full support and has metric entropy equal to the given constant. Similar results also hold for suspension flows over transitive subshifts of finite type, Cr(r≥2)-generic geometric Lorenz attractors and C1-generic singular hyperbolic attractors.

Stability properties of singular suspension flows

The singular suspension flow is a kind of suspension for homeomorphisms on metric spaces in which non-isolated singularities are allowed. First, we analyze the topological stability of singular suspension flows. Secondly, we show that the singular suspension of any expansive homeomorphism is both k*-expansive and rescaling expansive. Furthermore, there exists a homeomorphism that is not expansive though its singular suspension is rescaling expansive.

Streamwise Turbulence Modulation in Non‐Uniform Open‐Channel Clay Suspension Flows

AbstractCohesive sediment particles are ubiquitous in environmental flows. The cohesive properties of clay promote the formation of clay flocs and gels and relatively small suspended clay concentrations can enhance or suppress turbulence in a flow. Furthermore, flows are naturally non‐uniform, varying in space and time, yet the dynamics of non‐uniform open‐channel clay suspension flows is poorly understood. For the first time, the adaptation time and length scales of non‐uniform clay suspension flows were quantified using novel experiments with spatially varying but temporally uniform flow. Different levels of turbulence enhancement and attenuation were identified as the flow decelerates or accelerates. Results highlight that decelerating clay suspension flows crucially have a longer adaptation time than accelerating clay suspension flows. This is explained by the longer timescale required for the formation of bonds between cohesive particles in turbulence attenuated flows after deceleration than the rapid breakdown of bonds in turbulent flows after acceleration of clay suspension flows. This hysteresis is more pronounced for higher concentration decelerating flows that pass through a larger variety of clay flow types of turbulence enhancement and attenuation. These different adaptation time scales and associated clay flow type transitions are likely to affect clay flow dynamics in a variety of fluvial and submarine settings.

A fully resolved smoothed particle hydrodynamics-discrete element method study of the rheology of suspensions: The role of inertia and grain shape

This paper presents a numerical study on suspensions of monodisperse non-Brownian grains in a Couette flow. The fully resolved coupled smoothed particle hydrodynamics and discrete element method is employed to model the motion of arbitrarily shaped grains in a viscous fluid. The numerical method is benchmarked against its capability in accurately handling grain–fluid hydrodynamics and inter-grain collisions. It is then used to simulate suspension flows of varying particle Reynolds and Bagnold numbers subjected to different shear rates, solid concentrations, and solid-to-fluid density ratios. A special focus is placed on the effect of grain shape with different aspect ratios and convexities on the flow behavior. Both the inertia and the grain shape are found to affect the grain–fluid and inter-grain interactions and uniquely contribute to the overall shear stress and the rheology of the suspension. The local profiles of solid concentration suggest the presence of grain layering near the boundary walls, which becomes more pronounced with higher solid concentration and inertia, and increased non-circularity in grain shape. A further examination of the pair distribution function and average particle rotation reveals a strong correlation between suspension viscosity and grain microstructure and kinematics.

Strongly Isomorphic Symbolic Extensions for Expansive Topological Flows

Abstract In this paper, we prove that finite-dimensional topological flows without fixed points and having a countable number of periodic orbits, have the small flow boundary property. This enables us to answer positively a question of Bowen and Walters from 1972: Any expansive topological flow has a strongly isomorphic symbolic flow extension, that is, an extension by a suspension flow over a subshift. Previously Burguet had shown this is true if the flow is assumed to be $C^{2}$-smooth.

Hybrid Nanofluid Flow with Multiple Slips Over a Permeable Stretching/Shrinking Sheet Embedded in a Porous Medium

Including slip boundary conditions in the study involving the flow of foams, emulsions, polymer solutions, and suspensions over moving surfaces are crucial for real-life applications. The current study analysed the multiple slips effects on the magnetohydrodynamics (MHD) flow of Ag-CuO/water hybrid nanofluid past a permeable stretching/shrinking sheet embedded in a porous medium. Appropriate similarity variables are introduced for transforming the governing equations and boundary conditions into ordinary differential equations before being solved using the bvp4c solver. Dual solutions are yielded from the numerical computation of flow over a shrinking sheet, and the first solution is identified as stable through a stability analysis. It is found that the imposition of velocity, thermal, and mass slips promotes the reduction of momentum, thermal, and concentration boundary layer thickness, respectively. The hybrid nanofluid around the sheet is observed to flow at a different velocity from the sheet due to the imposition of velocity slip. Thermal and mass slips, meanwhile, obstruct the flow's ability to transport heat and mass. An increased suction parameter, however, can aid in enhancing the rates of heat and mass transfers.

Novel PDMS-based transparent suspensions suitable for fluid flow characterization by optical techniques

Optical measurement techniques, such as µPIV and LDV are widely used in experimental fluid dynamics to investigate pure fluids or suspension flows. Optical access is a major concern in suspension experimentation. The suspended particle material must have a refractive-index matching those of the base fluid and wall set-up. This work reports a novel refractive-index-matched transparent suspension. The particulate matter is comprised of sub-10 µm spherical PDMS particles. PMDS is a widely used material to manufacture microchannels due to its low-refractive-indexand non-toxicity. PDMS microparticles were produced and suspended in a refractive-index matching base fluid (DMSO aqueous solution) and two transparent suspension concentrations were formulated [∼ 10% and ∼ 18% (w/w)]. Suspension rheology was characterized, andoptical properties analysed. μPIV successfully measured the velocity flow of the transparent suspensions in a circular-section microchannel, and the velocity profiles agreed well with the analytical solution.

On the flow of soft suspensions through orifices

The behavior of confined suspensions of soft droplets under pressure-driven flow, passing an obstacle within a planar channel, is investigated by means of a mesoscopic lattice Boltzmann model capable of simulating soft non-coalescing droplets. The simulations reveal that the threshold of the pore size, below which the flux vanishes, is between 1 and 2 droplet diameters, and increases with the packing fraction. Moreover, we show that the classical Beverloo relation between the total flux and the pore size is not suitable for the soft suspensions considered here.

Electrothermoplasmonic flow in gold nanoparticles suspensions: Nonlinear dependence of flow velocity on aggregate concentration

Efficient mixing and pumping of liquids at the microscale is a technology that is still to be optimized. The combination of an AC electric field with a small temperature gradient leads to a strong electrothermal flow that can be used for multiple purposes. Combining simulations and experiments, an analysis of the performance of electrothermal flow is provided when the temperature gradient is generated by illuminating plasmonic nanoparticles in suspension with a near-resonance laser. Fluid flow is measured by tracking the velocity of fluorescent tracer microparticles in suspension as a function of the electric field, laser power, and concentration of plasmonic particles. Among other results, a non-linear relationship is found between the velocity of the fluid and particle concentration, which is justified in terms of multiple scattering-absorption events, involving aggregates of nanoparticles, that lead to enhanced absorption when the concentration is raised. Simulations provide a description of the phenomenon that is compatible with experiments and constitute a way to understand and estimate the absorption and scattering cross-sections of both dispersed particles and/or aggregates. A comparison of experiments and simulations suggests that there is some aggregation of the gold nanoparticles by forming clusters of about 2–7 particles, but no information about their structure can be obtained without further theoretical and experimental developments. This nonlinear behavior could be useful to get very high ETP velocities by inducing some controlled aggregation of the particles.

Margination of platelet-sized particles in red blood cell suspensions flowing through a Y-shaped confluence microchannel

In blood flow through microvessels, platelets are known to be distributed in high concentrations near the vessel wall, termed ‘margination’ or ‘near-wall excess’. At the confluence of two vessels, this preferential distribution of platelets is thought to be compromised and reconstituted in the downstream main vessel. The present study aimed to investigate the distance of this margination reconstruction from the confluence by in vitro experiments using platelet-sized fluorescent particles as a platelet surrogate and a Y-shaped confluence microchannel with rectangular cross sections. Fluorescence microscopy was performed using a confocal laser scanning microscope system to measure the distribution of particles in the red blood cell suspension flow. Immediately after confluence, particles were highly concentrated along a narrow band in the middle of the channel width, where particles located near the inner wall of the daughter channels flowed in. This dense band of particles faded downstream and disappeared less than 5 mm from the confluence. This margination distance is comparable to or smaller than the margination development distance in straight channels, but much smaller than that after bifurcation.

Investigation of a novel Couette flow with cylindrical baffles

The high-precision measure instrument for flow velocity is essential for industrial applications because the high-precision velocity can well reflect the physical characteristic of the flow. A restricted laminar Couette flow with cylindrical baffles, using a synthetic heat conduction liquid, was designed to obtain a steady vortex flow and wider work scope, according to Couette flow and Suspension flow characteristics. The heat transfer mechanism was investigated with a laminar flow model by the Fourier law. The research indicates that the heat transfer enhancement is related to the Temperature Boundary Layer (TBL). The TBL is affected by the Velocity Boundary Layer (VBL). The TBL thickness and Nusselt number (Nu) have a dependent relationship. The Reynolds number (Re) and the gap between the baffle and plate wall (Δh/h) can further affect Nu. The vortex flow generated by Couette flow can significantly enhance the heat transfer performance by a double spiral structure, which can rapidly mix heat fluxes and make the temperature converge to uniform. There is a sensitive and stable relationship between flow velocity and heat transfer. Notably, it is linear when Δh/h or Re is small, which can be used to design a high-precision thermal flow velocity meter.

Towards the use of probability distribution function to describe the flow of fiber suspensions

Towards the use of probability distribution function to describe the flow of fiber suspensions

A discourse on factors influencing the formation of sigmoidal and linear slope-geometries in the deltaic clinoforms of the calciclastic Sobrarbe Delta, Ainsa Basin, Spain

Clinoforms develop at the hearts of prograding sedimentary systems and are an integral part in understanding basin development and sediment partioning. The Eocene Sobrarbe Formation in the Ainsa Basin in Spain, displays well-developed dipping clinoform geometries. The study observes depositional facies, mineralogy, and performs curve-fitting calculations in 2D to better understanding of factors controlling clinoform geometries.The Sobrarbe Formation is a unique prograding calciclastic delta system, in which carbonates are dominant, but depositional environments and sedimentary processes are akin to silicilclastic systems.Four clinothems (CT 1–4) were selected for detailed study. The clinothems display an overall coarsening upward trend. The lowermost clinothems comprise dominantly pro-deltaic marlstone deposited from suspension and dilute hyperpycnal flows, with occasional thin fine-grained episodic turbidite beds. The uppermost clinothems are dominated by reworked remobilized topset deposits comprising bioturbated calcarenites with a variety of trace-fossils, shells and large assemblages of nummulites, and finally proximal subaqueous stacked calcarenites.Three clinothems (1, 2, 4) are characterized by sigmoidal geometry (Gaussian distribution curve), symmetrical sediment distribution, a simple coarsening upward trend, and where calculable, ascending regressive trajectories. Clinothem 3 comprises a more complex stratigraphic development and displays an overall ascending transgressive trajectory, linear slope and asymmetric sediment distribution.The results show that sigmoidal geometries develop in both the distal pro-delta and in the coarser-grained proximal delta, suggesting the sigmoidal form develops naturally granted sufficient accommodation. While speculative it appears that linear slopes might be associated with draping during transgression, and asymmetric distribution associated with high sedimentation rates vis a vis accommodation. Accommodation exerts the dominant control on the location of the rollover and the trajectory. The topset-foreset ratio indicates the relative rate of sedimentation compared to accommodation, as high sedimentation rates increase deposition on the foreset. Results indicate that accommodation appears to be the most important factor controlling foreset slope, with steeper inclination developing in deeper water. Meanwhile sedimentation rate, grain size, and the role of turbidity currents may play a secondary role influencing slope angle.

P204 Biomechanical Phenotype of Circulating Neutrophils Is Altered in ANCA Associated Vasculitis

Abstract Background/Aims Real Time-Deformability Cytometry (RT-DC) is a novel technique able to identify morpho-rheological characteristics of individual cells such as size, deformability, and elasticity using only 50µl of whole blood. Cells in suspension flow through a microfluidic channel while hydrodynamic force is applied, leading to reversible deformation of individual cells from shear stress and pressure gradients. Cell brightness and area can be used to identify individual cell types. The morpho-rheological characteristics of immune cells in ANCA associated vasculitis (AAV) are unknown. Methods Whole blood from healthy controls (HC), patients with active AAV, or patients with AAV in remission was analysed using RT-DC. The diagnosis of AAV was based upon positive ANCA testing, with either (i) pauci-immune glomerulonephritis, or (ii) typical clinical features of extra-renal AAV. Patients with active disease may have received steroids prior to sampling but those who received other immunosuppression or cytotoxics were excluded. Remission was defined as BVAS of 0 with prednisolone dose ≤7.5mg/day. Blood was collected into K2 EDTA and diluted 1:20 in 1xPBS/0.6% methylcellulose. Cell suspensions were flowed across a Flic20 polydimethylsiloxane microfluidic chip, containing reservoirs connected by a measurement channel with a 20x20 μm2 cross-section. RT-DC measurements were collected at a flow rate of 0.12μL/s using a high-speed CMOS camera to capture images at a rate of 2000 frames/second. ShapeOut software was used to calculate cell size, deformation, and elasticity. Results There was no difference in neutrophil size between patients with active AAV (n = 15), patients with AAV in remission (n = 31), and HC (n = 15). Neutrophils from patients with active AAV were significantly stiffer than patients in remission or HC, displaying decreased deformation (median 0.084, 0.085, and 0.078 au respectively, p = 0.0068) and increased elasticity (median 0.973, 0.968 and 1.006 au respectively, p = 0.0196). In patients with active AAV, there was strong inverse correlation between neutrophil deformation and disease activity measured by BVAS score (r=-0.573, p = 0.032). Neutrophils isolated from healthy donors exhibited a trend towards decreased deformability when primed with TNF and stimulated with MPO-ANCA IgG compared to unstimulated or cells treated with healthy donor IgG (median 0.086, 0.085, and 0.083 for unstimulated, control IgG, and MPO-ANCA IgG respectively, ns). Conclusion Neutrophils from patients display distinct physical properties in active AAV which correlate with disease activity. Similar results are seen when neutrophils are stimulated in vitro with MPO-ANCA IgG. This phenotype of increased cell stiffness may lead to increased neutrophil retention in pulmonary and renal microvasculature, thus increasing the potential for neutrophil-endothelial cell interactions and microvascular damage. Morphorheological parameters can be rapidly measured using a small volume of whole blood; thus, RT-DC may be a useful technique to aid identification of disease activity in AAV and to guide treatment. Disclosure N. Pisacano: None. S.P. McAdoo: None. J. Guck: None. C.D. Pusey: None. E.R. Chilvers: None. A.C. Cowburn: None. K.M. Lodge: None. M.F. Prendecki: None.

The influence of fibrous suspension flow regimes on the formation of tissue paper manufactured from different furnish compositions

Abstract The present work was based on analysis of the flow regime of fibre suspensions, that corresponds to furnishes and process conditions typically established for tissue paper manufacturing, i.e., under the common range of stock consistencies at the machine headbox and most usual furnish compositions. The flocculation potential of fibre suspensions used for toilet papers, facial tissues, paper towels and table napkins were evaluated on the principles of analytical concepts for fibre agglomeration propensity. The results show crowding numbers from 5.0 to 69.0, depending on the type of fibre or fibre blending ratios. The findings regarding agglomeration factors indicate that flow regimes are mainly in semi-concentrated and around gel state zones but reached the concentrated flow regime, in extreme conditions of fibre morphology and stock consistency. The influence of hardwood and softwood mixture ratios on the fibre suspension features is shown and discussed for common formulations of tissue base paper. The effect of fibre length and coarseness on the flocculation potential and the impacts of fibre suspension flow regimes on the structural properties of tissue paper, such as the formation uniformity are discussed, demonstrating the reasons for the preferred use of high hardwood content in furnish balance for tissue paper manufacturing.

Particle laden flows around a circular cylinder from the hydrodynamic to granular regime

The flow around a circular cylinder is studied with the presence of solid finite-size spherical particles. The simulations of suspension flows are based on highly efficient simulation algorithms to generate scalable Lattice Boltzmann Method calculations. Simulations of particle resolved dynamics with up to 4800 million grid cells and 1.8 million spherical particles are carried out for different flow regimes and particle concentrations (from dilute, 5% volume concentration to semi-dilute regime, 20%). We investigated a range of parameters that spans from suspensions of iso-dense particles to highly inertial particles in a granular flow, while considering particle to cylinder diameter ratios of 5 and 10.The flow response is described by characteristic properties such as vortex shedding frequency or wake recirculation length. Flow regimes with iso-dense particles can be rationalized by means of mixture material properties while we observe a progressive transition to granular flow for inertial particles. Drag and lift forces acting onto the cylinder are presented in time and frequency domains and the physical analysis is based on the respective hydrodynamic and particle collision contributions.

Analysis of the Dynamics of Water Flow and Suspension Flow Discharge in Volcano Watershed with Settlement Land Use

Suspension flow into the upstream of volcano watershed is sensitive to land use. In Indonesia, a settlement is a form of land use in several volcanic landscapes. There is currently no detailed study on the suspension flow sediment from the settlement land use. The purpose of this study is to investigate the characteristics of the relationship between water and suspension flow discharge. The study was conducted through the measurements at a gully outlet that produced 747 suspension load data. For each rainfall event, suspension load measurements were made in the field, followed by laboratory analysis. Additionally, field surveys were used to determine the characteristics of settlement land use and the water flow into the gully system. According to the findings, the peak flow discharge corresponds to the peak suspension discharge, the peak flow discharge comes before the peak suspension discharge, and the peak flow discharge happens after the peak suspension discharge. The average time lag between initial rainfall events and suspension flow was 10.36 minutes, and the suspension peak content varied by an average of 2.22 gl-1. The grain size was also dominated by the clay fraction, averaging 67.86% on the ascending branch and 67.82% on the descending branch.
 Keywords: Erosion; Discharge; Settlements; Suspension; Watershed
 
 Copyright (c) 2023 Geosfera Indonesia and Department of Geography Education, University of Jember
 This work is licensed under a Creative Commons Attribution-Share A like 4.0 International License

Effects of cell deformability and adhesion strength on dynamic cell seeding: Cell-scale investigation via mesoscopic modeling

The flow of cell suspension through a porous scaffold is a common process in dynamic cell seeding, which determines the initial distribution of cells for constructing tissue-engineered grafts. Physical insights into the transport and adhesion behaviors of cells in this process are of great significance to the precise control of cell density and its distribution in the scaffold. Revealing of dynamic mechanisms underlying these cell behaviors through experiments is still difficult. The numerical approach therefore plays an important role in such studies. However, existing studies have mostly focused on external factors (e.g., flow conditions and scaffold architecture) but ignored the intrinsic biomechanical properties of cells as well as their associated effects. The present work utilized a well-established mesoscopic model to simulate the dynamic cell seeding within a porous scaffold, based on which a thorough investigation of the effects of cell deformability and cell-scaffold adhesion strength on the seeding process was carried out. The results show that the increase in either the stiffness or the bond strength of cells would augment the firm-adhesion rate and thus enhance seeding efficiency. In comparison to cell deformability, bond strength seems to play a more dominant role. Especially in the cases with weak bond strength, remarkable losses of seeding efficiency and distribution uniformity are observed. Noteworthily, it is found that both the firm-adhesion rate and the seeding efficiency are quantiatively related to the adhesion strength which is measured as the detachment force, suggesting a straightforward way to estimate the seeding outcome.

How colored noise shifts the boundaries of oscillatory zones in suspension flows

A mathematical model of the suspension flow forced by colored random disturbances is considered. We focus on the parameter zone adjacent to the Andronov–Hopf bifurcation separating stable equilibrium and self‐oscillatory modes. A phenomenon of stochastic excitement with colored‐noise‐induced generation of spiking oscillations in the equilibrium zone is investigated. We show how colored noise shifts boundaries of oscillation modes, and study dependence of this shift on the correlation time parameter. Zones of the stochastic resonance are revealed and parametrically described in terms of probability of excitement.

Gas dynamics of stationary supersonic gas jets with inert particles exhausting into a medium with low pressure

Issues related to the development of tools for mathematical modeling of stationary supersonic flows of an ideal compressible gas with inert particles are considered. A mathematical model is constructed that describes the flow of an inviscid compressible gas with inert particles in a jet flowing from an axisymmetric nozzle into a flooded space. Provided that the flow is supersonic along one of the spatial coordinates, the Euler equations are hyperbolic along this coordinate. For numerical calculations of the gas flow field, the finite volume method and the marching method are used. For integration over the marching direction, the three-step Runge–Kutta scheme is used. The procedure for calculating the flows includes the reconstruction of the values of the desired functions on the faces of the control volumes from the average values over the control volumes and the solution of the problem of the decay of an arbitrary discontinuity (the Riemann problem). The Lagrangian method of test particles is used to describe the dispersed phase. The effects of the reverse influence of particles on the flow of the carrier gas are not taken into account. The effects of viscosity and rarefaction of the gas flow are taken into account only when the gas interacts with particles. Calculation of the trajectories of inert particles is carried out in a known flow field of the carrier gas. The motion trajectories of discrete inclusions in jet flows with strong underexpansion are presented. The influence of the particle size and the coordinates of the particle entry point into the flow on the features of their transfer by the jet stream are discussed. Efficient means of numerical simulation of stationary supersonic flows of an ideal compressible gas with particles in nozzles and jets have been developed. The calculation results are of interest for studying supersonic gas suspension flows around bodies and for calculating oblique shock waves.