Channel Centerline Research Articles

Prediction of floodwater impacts on vehicle blockages at bridges using artificial neural network

During extreme flood events, various debris like floating vehicles can block the bridges in urban rivers and floodplains. Blockage of vehicles can influence the floodwater hydrodynamics and potentially on the flood risk implications. Such obstructions often raise upstream water levels with back water effects, causing more water to be redirected into nearby metropolitan areas. This study attempts at evaluating artificial neural network (ANN) model in predicting the variations in floodwater depths and velocities along the channel centreline based on the changes in flowrate and distances from the inlet. The floodwater depth and velocity variations were obtained for three different types of bridges at specified sites along the channel centreline with three incoming discharges. A multilayer feedforward neural network (FFNN) model was used to investigate the effects of discharge (Q) and distance, on depth variation rate (D) or velocity (V). Additionally, a comparison study was done between 2 input 1 output and 2 input 2 output i.e. single output (depth variation rate (D) or velocity (V) versus multi-output depth variation rate (D) and velocity (V) for all the three models of bridges that are blocked by vehicles. The study has applied 12 training algorithms (TA) in the ANN modelling to optimize the TA that is most suitable for the dataset of three different bridges. The optimization is based on the performance criterion namely regression (R), mean squared error (MSE), mean absolute error (MAE), mean absolute percentage (MAPE), accuracy and coefficient of determinant (R2). Bayesian regularization backpropagation (BR) training algorithm gives a highest accuracy when compared in all three bridges. The scenario 2 input 2 output gave greatest accuracy results compared to 2 input 1 output. The findings showed a reliable estimation of significant impacts on the flow propagations and the hydrodynamic processes along rivers and floodplains. This study can help the decision makers in effective river and floodplain management practices.

A universal velocity profile for turbulent wall flows including adverse pressure gradient boundary layers

A recently developed mixing length model of the turbulent shear stress in pipe flow is used to solve the streamwise momentum equation for fully developed channel flow. The solution for the velocity profile takes the form of an integral that is uniformly valid from the wall to the channel centreline at all Reynolds numbers from zero to infinity. The universal velocity profile accurately approximates channel flow direct numerical simulation (DNS) data taken from several sources. The universal velocity profile also provides a remarkably accurate fit to simulated and experimental flat plate turbulent boundary layer data including zero and adverse pressure gradient data. The mixing length model has five free parameters that are selected through an optimization process to provide an accurate fit to data in the range $R_\tau = 550$ to $R_\tau = 17\,207$ . Because the velocity profile is directly related to the Reynolds shear stress, certain statistical properties of the flow can be studied such as turbulent kinetic energy production. The examples presented here include numerically simulated channel flow data from $R_\tau = 550$ to $R_\tau =8016$ , zero pressure gradient (ZPG) boundary layer simulations from $R_\tau =1343$ to $R_\tau = 2571$ , zero pressure gradient turbulent boundary layer experimental data between $R_\tau = 2109$ and $R_\tau = 17\,207$ , and adverse pressure gradient boundary layer data in the range $R_\tau = 912$ to $R_\tau = 3587$ . An important finding is that the model parameters that characterize the near-wall flow do not depend on the pressure gradient. It is suggested that the new velocity profile provides a useful replacement for the classical wall-wake formulation.

Effects of obstacle layout and blockage ratio on flame acceleration and DDT in hydrogen-air mixture in a channel with an array of obstacles

Numerical simulations were performed to study flame acceleration and deflagration-to-detonation transition (DDT) in hydrogen-air mixture in a channel with a two-dimensional array of cylindrical obstacles. A high-order numerical algorithm with adaptive mesh refinement was applied to solve reactive Navier-Stokes equations. The effect of obstacle layout was examined by considering three layouts at a fixed blockage ratio of 0.5: staggered, inline-concentrated, and inline-scattered. Three blockage ratios, 0.33, 0.5, and 0.67, were used for the case of staggered obstacles to explore the influence of blockage ratio. The results show that both obstacle layout and blockage ratio have significant effects on flame acceleration and DDT occurrence, although the basic mechanism of detonation initiation is consistent for all the cases involving shock focusing. In the staggered case, the head-on collisions of flame and pressure waves with obstacles greatly promote the growth of flame surface area and thus lead to the fastest flame acceleration and shortest detonation onset time. In the inline-concentrated case, flame propagates slower than that in the staggered case due to smaller flame surface area. However, compared to the zigzag path in the staggered case, the straight passages parallel to flame propagation direction in the inline-concentrated case are more conducive to producing strong shock focusing and thus result in the shortest DDT distance. In the inline-scattered case, the straight passage along the centerline of channel facilitates the early acceleration of flame, but it has the slowest flame propagation in lateral directions and thereby the longest DDT time and distance. For the staggered obstacles at different blockage ratios, flame acceleration rate increases with increasing blockage ratio. The occurrence of DDT is hindered by the most congested obstacles, because the shock focusing is insufficiently strong to initiate detonation after passing through the excessively narrow gaps.

Approach to the 4/3 law for turbulent pipe and channel flows examined through a reformulated scale-by-scale energy budget

In this study, we propose a scale-by-scale (SBS) energy budget equation for flows with homogeneity in at least one direction. This SBS budget represents a modified form of the equation first proposed by Danaila et al. (J. Fluid Mech., vol. 430, 2001, pp. 87–109) for the channel centreline – the primary difference is that, here, we consider the role of pressure along with the errors associated with the isotropic approximations of the interscale divergence and Laplacian of the squared velocity increment. The term encompassing the effects of mean shear is also characterised such that the present analysis can be extended straightforwardly to locations away from the centreline. We show, based on a detailed analysis of previously published channel flow direct numerical simulations and pipe flow experiments near the centreline, how several terms in the present SBS budget equation (including the third-order velocity structure function) behave with increasing Reynolds number. The behaviour of these terms is shown to imply a rate of emergence and subsequent growth of the 4/3 law scale subrange at the channel centreline and pipe axis. The analysis also suggests that the peak magnitude of the third-order velocity structure function occurs at a scale that is fixed in proportion to the Taylor microscale at sufficiently high Reynolds number.

Giant meandering channel evolution, Campos deep-water salt basin, Brazil

AbstractSubmarine channels are conduits for sediment delivery to continental margins, and channel deposits can be sandy components of the fill in tectonically active salt basins. Examples of salt-withdrawal basin fill commonly show successions of sandy channelized or sheet-like systems alternating with more mud-rich mass-transport complexes and hemipelagites. This alternation of depositional styles is controlled by subsidence and sediment-supply histories. Salt-basin fill comprising successions of largely uninterrupted meandering-channel deposition are less commonly recognized. This begs the questions: can sediment supply be large enough to overwhelm basin subsidence and result in a thick succession of channel deposits, and, if so, how would such a channel system evolve? Here, we use three-dimensional seismic-reflection data from a >1500 km2 region with salt-influenced topography in the Campos Basin, offshore Brazil, to evaluate the influence of salt diapirs on an Upper Cretaceous–Paleogene giant meandering submarine-channel system (channel elements >1 km wide; meander wavelengths several kilometers to >10 km). The large scale of the channels in the Campos Basin suggests that sediment discharge was large enough to sustain the meandering channel system in spite of large variability in subsidence across the region. We interpreted 22 channel centerlines to reconstruct the detailed kinematic evolution of this depositional system; this level of detail is akin to that of recent studies of meandering fluvial channels in time-lapse Landsat satellite images. The oldest channel elements are farther from salt diapirs than many of the younger ones; the centerlines of the older channel elements exhibit a correlation between curvature and migration rate, and a spatial delay between locations of peak curvature and maximum migration distance, similar to that observed in rivers. As many of the younger channel centerlines expanded toward nearby salt diapirs, their migration pattern switched to downstream translation as a result of partial confinement. Channel segments that docked against salt diapirs became less mobile, and, as a result, they do not show a correlation between curvature and migration rate. The channel migration pattern in the Campos Basin is different compared to that of a tectonically quiescent continental rise where meander evolution is unobstructed. This style of channelized basin filling is different from that of many existing examples of salt-withdrawal minibasins that are dominated by overall less-channelized deposits. This difference might be a result of the delivery of voluminous coarse sediment and high discharge of channel-forming turbidity currents to the Campos Basin from rivers draining actively uplifting coastal mountains of southeastern Brazil. Detailed kinematic analysis of such well-preserved channels can be used to reconstruct the impact of structural deformation on basin fill.

Performance comparison of a 9-kW magnetically shielded Hall thruster operating on xenon and krypton

The performance of a 9-kW class magnetically shielded Hall thruster operating on xenon and krypton propellants is experimentally characterized. Thrust and efficiency measurements performed at discharge powers ranging from 4.5 to 9 kW indicate that the anode efficiency of krypton is 9%–18% lower than that of xenon. This difference is comparable to previous measurements reported for unshielded Hall thrusters, although it is found that unlike in previous studies, the efficiency ratio widens with increasing discharge voltage. Far-field probes are employed to measure the contributions to anode efficiency at conditions of 4.5 and 6 kW. These results indicate that mass utilization has the largest impact on the difference in performance between xenon and krypton. Assuming this mass utilization remains the dominant driver at higher voltages, it is proposed that the higher electron temperature of shielded thrusters along channel centerline coupled with the nonlinearity of the ionization cross section may explain why the efficiency gap widens with increasing voltage for shielded thrusters. The results are discussed in the context of optimizing magnetically shielded Hall thrusters for improved performance on krypton propellant.

A numerical study of particle-laden flow around an obstacle: flow evolution and Stokes number effects

Three-way coupled numerical simulations of particle-laden fluid flow around a square obstacle are performed by a coupled finite-volume and discrete-element method, taking account of the collisions between particles. The fluid flow is described by the Eulerian formalism, while the Lagrangian formalism is used for the solid particles. The dynamics of each phase and the modulation mechanism of the flow field by the inertial particles are explored. The Reynolds number based on the side length of the obstacle is 100, which leads to a typical periodic flow pattern of vortex shedding. Under the action of particles, the flow tends to be chaotic even in the upstream region, and the vortex shedding occurs earlier. The intensity of the vortex is attenuated due to particle dissipation. At sufficiently small Stokes numbers, the particles exhibit flow tracer behavior with relatively high fidelity. However, as the Stokes number and mass loading increase, the interaction between the particles and fluid becomes important, especially in the core region of the channel. With the increase of the particle response time, the spanwise velocity fluctuation is attenuated, while the influence on the streamwise velocity fluctuation seems complicated. No particles are observed to hit the rear surface of the obstacle or deposit in the domain during the flow. When the Stokes number and mass loading are elevated from 0.0036 and 0.065 to 0.5 and 9.024, respectively, the distribution of the particles near the channel centerline varies from being filled in the shedding vortices to surrounding them. Meanwhile, the particle-free zones centered on these vortices become larger. For the Stokes number and mass loading up to 1.5 and 27.073, respectively, the particles are scattered in the downstream area, and the flow pattern of the Kármán vortex street is modified. Within the range of the Stokes number considered, the drag and lift coefficients, and the Strouhal number also show a certain trend of variation.

Two-dimensional diffusion biased by a transverse gravitational force in an asymmetric channel: Reduction to an effective one-dimensional description.

We focus on the derivation of a general position-dependent effective diffusion coefficient to describe two-dimensional (2D) diffusion in a narrow and smoothly asymmetric channel of varying width under a transverse gravitational external field, a generalization of the symmetric channel case using the projection method introduced earlier by Kalinay and Percus [P. Kalinay and J. K. Percus, J. Chem. Phys. 122, 204701 (2005)10.1063/1.1899150]. To this end, we project the 2D Smoluchowski equation into an effective one-dimensional generalized Fick-Jacobs equation in the presence of constant force in the transverse direction. The expression for the diffusion coefficient given in Eq.(34) is our main result. This expression is a more general effective diffusion coefficient for narrow 2D channels in the presence of constant transverse force, which contains the well-known previous results for a symmetric channel obtained by Kalinay, as well as the limiting cases when the transverse gravitational external field goes to zero and infinity. Finally, we show that diffusivity can be described by the interpolation formula proposed by Kalinay, D_{0}/[1+(1/4)w^{'2}(x)]^{-η}, where spatial confinement, asymmetry, and the presence of a constant transverse force can be encoded in η, which is a function of channel width (w), channel centerline, and transverse force. The interpolation formula also reduces to well-known previous results, namely, those obtained by Reguera and Rubi [D. Reguera and J. M. Rubi, Phys. Rev. E 64, 061106 (2001)10.1103/PhysRevE.64.061106] and by Kalinay [P. Kalinay, Phys. Rev. E 84, 011118 (2011)10.1103/PhysRevE.84.011118].

Numerical study of single bubble mobility in triangular and deltoid microchannels using the boundary element method

The study of bubbly liquid dynamics in microchannels of unconventional shapes is of great importance for different fields of science and industry. This work investigates the dynamics of the incompressible single bubbles in the slow periodic flow of viscous liquid in a triangular channel with a variable pressure gradient. The numerical approach used in this research is based on the boundary element method (BEM). This method is widely used for solving three-dimensional problems and problems in areas with complex geometry. The influence of the bubble’s initial position relative to the channel centerline on the bubble deformation, the relative velocity of the bubble, and its center of mass displacement in the channel are considered.

Matching characteristics of magnetic field configuration and chamfered channel wall in a magnetically shielded Hall thruster

To date, the selection of the magnetic field line used to match the chamfered inner and outer channel walls in a magnetically shielded Hall thruster has not been quantitatively studied. Hence, an experimental study was conducted on a 1.35 kW magnetically shielded Hall thruster with a xenon propellant. Different magnetic field lines were chosen, and corresponding tangentially matched channel walls were manufactured and utilized. The results demonstrate that high performance and a qualified anti-sputtering effect cannot be achieved simultaneously. When the magnetic field lines that match the chamfered wall have a strength at the channel centerline of less than 12% of the maximum field strength, the channel wall can be adequately protected from ion sputtering. When the magnetic field lines have a strength ratio of 12%–20%, the thruster performance is high. These findings provide the first significant quantitative design reference for the match between the magnetic field line and chamfered channel wall in magnetically shielded Hall thrusters.

Neutrally Buoyant Particle Migration in Poiseuille Flow Driven by Pulsatile Velocity.

A neutrally buoyant circular particle migration in two-dimensional (2D) Poiseuille channel flow driven by pulsatile velocity is numerical studied by using immersed boundary-lattice Boltzmann method (IB-LBM). The effects of Reynolds number () and blockage ratio on particle migration driven by pulsatile and non-pulsatile velocity are all numerically investigated for comparison. The results show that, different from non-pulsatile cases, the particle will migrate back to channel centerline with underdamped oscillation during the time period with zero-velocity in pulsatile cases. The maximum lateral travel distance of the particle in one cycle of periodic motion will increase with increasing , while has little impact. The quasi frequency of such oscillation has almost no business with and . Moreover, plays an essential role in the damping ratio. Pulsatile flow field is ubiquitous in aorta and other arteries. This article is conducive to understanding nanoparticle migration in those arteries.

Experiments on Longitudinal and Transverse Bedload Transport in Sine-Generated Meandering Channels

Bedload grains in consecutive meandering bends either move longitudinally or across the channel centerline. This study traces and quantifies the grains’ movement in two laboratorial sine-generated channels, i.e., one with deflection angle θ0 = 30° and the other 110°. The grains originally paved along the channels are uniform in size with D = 1 mm and are dyed in various colors, according to their initial location. The experiments recorded the changes in the flow patterns, bed deformation, and the gain-loss distribution of the colored grains in the pool-bar complexes. We observed the formation of two types of erosion zones during the process of the bed deformation, i.e., Zone 1 in the foreside of the point bars and Zone 2 near the concave bank downstream of the bend apexes. Most grains eroded from Zone 1 are observed moving longitudinally as opposed to crossing the channel centerline. Contrastingly, the dominant moving direction of the grains eroded from Zone 2 changes from the longitudinal direction to the transversal one as the bed topography evolves. Besides, most building material of the point bars comes from the upstream bends, although low- and highly curved channels behave differently.

Secondary-flow-aided single-train elastic-inertial focusing in low elasticity viscoelastic fluids.

Elastic-inertial focusing has attracted increasing interest in recent years due to the three-dimensional (3D) single-train focusing ability it offers. However, multi-train focusing, instead of single-train focusing, was observed in viscoelastic fluids with low elasticity as a result of the competition between inertia effect and viscoelasticity effect. To address this issue, we employed the secondary flow to facilitate single-train elastic-inertial focusing in low elasticity viscoelastic fluids. A three-section contraction-expansion channel was designed to induce the secondary flow to pinch the multiplex focusing trains into a single one exactly at the channel centerline. After demonstrating the focusing process and mechanism in our device, we systematically explored and discussed the effects of particle diameter, operational flow rate, polymer concentration, and channel dimension on particle focusing performances. Our device enables single-train focusing of particles in viscoelastic fluids with low elasticity, and offers advantages of planar single-layer structure, and sheathless, external-field free operation.

Numerical simulations of viscoelastic particle migration in a microchannel with triangular cross-section.

The migration of a spherical particle immersed in a viscoelastic liquid flowing in a microchannel with a triangular cross‐section is investigated by direct numerical simulations under inertialess conditions. The viscoelastic fluid is modeled through two constitutive equations to investigate the effect of the second normal stress difference and the resulting secondary flows on the migration phenomenon. The results are presented in terms of trajectories followed by the particles released at different initial positions over the channel cross‐section in a wide range of Weissenberg numbers and confinement ratios.Particles suspended in a fluid with a negligible second normal stress difference migrate toward the channel centerline or the closest wall, depending on their initial position. A much more complex dynamics is found for particles suspended in a fluid with a relevant second normal stress difference due to the appearance of secondary flows that compete with the migration phenomenon. Depending on the Weissenberg number and confinement ratio, additional equilibrium positions (points or closed orbits) may appear. In this case, the channel centerline becomes unstable and the particles are driven to the corners or “entrapped” in recirculation regions within the channel cross‐section. The inversion of the centerline stability can be exploited to design efficient size‐based separation devices.

Variations in Channel Centerline Migration Rate and Intensity of a Braided Reach in the Lower Yellow River

The Yellow River (YR) covers three climatic zones including arid region, semi-arid region and temperate monsoon region, with frequent appearance of flow intermittence in the Lower Yellow River (LYR) before 1999. Channel migration occurs frequently in braided rivers, which is a major focus of study in geomorphology and river dynamics. The braided reach in the LYR is featured by a complexly spatio-temporal variation in channel migration parameters owing to the varying condition of flow and sediment. It is crucial to investigate the migration characteristics of channel centerline for the sake of fully understanding channel evolution. A detailed calculation procedure is proposed to quantify migration rates and intensities of channel centerline at section- and reach-scales, using the measurements of remote sensing images and cross-sectional topography. Migration rates and intensities of channel centerline at section- and reach-scales from 1986 to 2016 were calculated, with the characteristics and key factors to control the migration intensity of channel centerline being identified quantitatively. Calculated results indicate that: (i) the mean probability of centerline migrating toward the left side was approximately equal to the probability of rightward migration from a long-term sequence; (ii) the mean reach-scale migration rate of channel centerline was reduced from 410 m/yr in 1986–1999 to 185 m/yr in 1999–2016, with a reduction of 55% owing to the Xiaolangdi Reservoir operation in 1999, and the mean reach-scale migration intensity of channel centerline was decreased from 0.28 to 0.16 m/(yr·m), with a reduction of 43%; (iii) the incoming flow-sediment regime was a dominant factor affecting the degree of channel migration, although the channel boundary conditions could influence the intensity of channel migration; and (iv) the reach-scale migration intensity of channel centerline can be written as a power function of the previous two-year average incoming sediment coefficient or fluvial erosion intensity, and the reach-scale migration intensities of channel centerline calculated using the proposed relations are generally in close agreement with the measurements over the period of 30 years.

Study on the polarity effect in an atmospheric pressure glow discharge driven by resonant power supply

In recent years, atmospheric pressure glow discharge has become an active research area for many scholars because of its broad industrial application prospects. However, much of the research is focused more on how to acquire this type of discharge or how to use it in some fields; there is a lack of clear and universally accepted theories. In this paper, we described the polarity effect in the process of atmospheric pressure glow discharge driven by a resonant power supply, from the standpoint of the differences in electric field direction in the pin-to-plate gap. We also discussed the characteristics of the discharge waveform, the characteristics of discharge images and the light-intensity distribution on the centerline of the discharge channel. Also studied were the polarity effect of unipolar discharge and the influence of different output-voltage amplitudes on the polarity effect. We found that both positive and negative discharges looked like a typical glow discharge. The voltage and current waveforms of unipolar discharge have a rapidly rising slope, and there is strong ionization near the anode. In the process of a unipolar discharge, there is an obvious γ discharge stage, and the α mode discharge has an obvious high-slope stage, whereas the slope of this process of a negative discharge is more gradual, and the polarity effects of positive and negative unipolar discharges become less and less obvious with the increase in the output-voltage amplitude of power supply.

Experimental investigation of spout incoherence in a spouted bed

Spout incoherence is a typical instability phenomenon in spouted beds, in which the particles in the spout region move upward as groups, leading to poor spouting stability and efficiency. In this paper, the moving particle blockage in the spout region is measured to quantify the spout incoherence for the first time, by means of depicting the regularity, frequency and particle blockage length of the spout incoherence phenomenon. Specifically, the particle blockage is quantified using the particle concentration obtained by image processing method based on intensity differences between gas and solid phase in the spout centreline. The centreline of the spout channel is located by the particle velocity vector field. The method is validated by visual observation and frequency analysis. Then, the effects of static bed height and spouting velocity on the spout incoherence are investigated, respectively. The results show that the main features of spout incoherence, including frequency, regularity and particle blockage length, remain constant with varying spouting velocity in the investigated range. The results reveal that the static bed height has significant effects on the spout incoherence, and the increasing bed height reduces the frequency and particle blockage length of spout incoherence. This work quantifies the spout incoherence and unveil many interesting mysteries of the spout incoherence in spouted beds.

Dynamics of concentrated suspensions in two-dimensional channel flow for non-Newtonian slurries

The evolution of concentrated particle suspensions in a two dimensional channel flow between parallel plates is considered. We developed a numerical model based on the finite volume method to solve the full unsteady Navier Stokes equations coupled to a constitutive advection-diffusion equation in order to determine shear-induced migration phenomenon in concentrated suspensions of monodisperse and non-colloidal spherical particles in two dimensions. The numerical model predicts the unsteady flow field, particle migration fluxes and gravitational mechanisms responsible of solids transport. The particle migration phenomena was studied in Newtonian and non Newtonian carrier fluids and the code was validated with both Newtonian and non-Newtonian carrier fluids solving the suspension advection-diffusion constitutive equation to determine the volume fraction contribution to the apparent viscosity of the fluid. In the case of a Newtonian carrier fluid the unsteady numerical simulations predicted a particle migration mechanism effectively occurring from high to low shear regions but evolving downstream. A cusped concentration profile was found at the channel centerline accompanied with a wall depletion region where the concentration was below the initial bulk value. The effect of gravity versus particle migration fluxes was studied though the introduction of initial uniform spot-like patches of bulk concentration in particular locations of the channel. For a Newtonian carrier, under the effect of a gravitational flux, the model predicts the formation of a sediment on the channel wall identified by an increase of local concentration similarly to the formation of a bottom bed found in mining slurries. In the case of a non-Newtonian Bingham carrier fluid without gravitational effects, the model predicts symmetrically cusped concentration profiles at the interface between yielded and unyielded regions and a particle depletion region close to each wall, where the particle concentration fall below the bulk concentration.

Impact of initial fiber states on different fiber dynamic patterns in the laminar channel flow

The dynamics of an elastic fiber with various initial states in a laminar channel flow is investigated using the immersed boundary-lattice Boltzmann method. Fiber-wall collisions are solved by adding a repulsive force in the model. Our simulation results demonstrate that the initial fiber state closely relates to the stability of the considered conveyance system. Different initial states may lead to different dynamic patterns in the downstream. The fiber is found to go straight forward along a horizontal path when it is horizontally and symmetrically placed at the channel centerline. Breaking this symmetry by varying the fiber's initial vertical position or orientation will induce the instability of the system, which then causes deviations and fluctuations in fiber's conveyance path. No matter how large the deviation occurs in the upstream, the fiber is always found to migrate to the channel central region in the downstream and would eventually settle in a vertical position slightly away from the channel centerline. Moreover, the off-centerline distance that a fiber settles depends on its dynamic pattern rather than a specific initial fiber state. For our system, there are two kinds of dynamic patterns observed in the downstream channel. In the first pattern, the fiber eventually reaches its equilibrium state and is observed to do a translational motion. In the second pattern, no equilibrium state is observable, and the fiber is found to do a periodically tumbling motion. The fiber's eventual conveyance speed depends on the vertical position it eventually settles and can be roughly approximated by the local flow velocity.

Viscoelastic particle focusing in human biofluids.

Saliva and blood plasma are non-Newtonian viscoelastic fluids that play essential roles in the transport of particulate matters (e.g., food and blood cells). However, whether the viscoelasticity of such biofluids alters the dynamics of suspended particles is still unknown. In this study, we report that under pressure-driven microflows of both human saliva and blood plasma, spherical particles laterally migrate and form a focused stream along the channel centerline by their viscoelastic properties. We observed that the particle focusing varied among samples on the basis of sampling times/donors, thereby demonstrating that the viscoelasticity of the human biofluids can be affected by their compositions. We showed that the particle focusing, observed in bovine submaxillary mucin solutions, intensified with the increase in mucin concentration. We expect that the findings from this study will contribute to the understanding of the physiological roles of viscoelasticity of human biofluids.