Simple Laminar Flow Research Articles

Mass distribution impacts on particle translation and orientation dynamics in dilute flows

We present a novel model for tracking particles (based on Lagrangian particle tracking) with inhomogeneous mass distribution. Without loss of generality, the presented approach captures inhomogeneity by assuming an offset spherical inclusion in an elongated ellipsoidal particle matrix. The model is first validated on simplified flow configurations such as particles settling in vacuum or air as well as suspended in simple shear and laminar pipe flow, where we achieved an excellent agreement with the available reference results. Furthermore, we investigate the impact of the inclusion parameters on the particle motion. Finally, the deposition of inhomogeneous particles in a simplified bifurcation is analyzed. We conclude that the consideration of inhomogeneity significantly alters the translational and orientational dynamics of the particles. Consequently, we advocate for the consideration of more realistic mass distributions to increase the accuracy of modeling and predicting the motion of inhomogeneous particles in flows for real-world applications.

A Microfluidic Strategy to Capture Antigen‐Specific High‐Affinity B Cells

Assessing B cell affinity to pathogen‐specific antigens prior to or following exposure could facilitate the assessment of immune status. Current standard tools to assess antigen‐specific B cell responses focus on equilibrium binding of the secreted antibody in serum. These methods are costly, time‐consuming, and assess antibody affinity under zero force. Recent findings indicate that force may influence BCR‐antigen binding interactions and thus immune status. Herein, a simple laminar flow microfluidic chamber in which the antigen (hemagglutinin of influenza A) is bound to the chamber surface to assess antigen‐specific BCR binding affinity of five hemagglutinin‐specific hybridomas from 65 to 650 pN force range is designed. The results demonstrate that both increasing shear force and bound lifetime can be used to enrich antigen‐specific high‐affinity B cells. The affinity of the membrane‐bound BCR in the flow chamber correlates well with the affinity of the matched antibodies measured in solution. These findings demonstrate that a microfluidic strategy can rapidly assess BCR‐antigen‐binding properties and identify antigen‐specific high‐affinity B cells. This strategy has the potential to both assess functional immune status from peripheral B cells and be a cost‐effective way of identifying individual B cells as antibody sources for a range of clinical applications.

- Increasing the Independence of Oyster Mushroom (Pleurotus ostreatus) Entrepreneurs in Seedlings Preparation

Sadam Mushroom House is one of the mushroom producers in Medan Marelan with oyster mushroom production of 7-12 kg/day and can accommodate 7,000 baglogs. The problem of the oyster mushroom business is still very dependent on mushroom nurseries in an effort to provide F2 seedlings because there are still very limited facilities, infrastructure, understanding and skills in providing F0 - F2 seeds. Another problem is that the baglogs waste produced (2,000-3,000 baglogs every 3 months) has not been used properly so that it has the potential to pollute the environment. The purpose of this community service is to increase the independence of partners in providing oyster mushroom seeds, making compost from baglog waste and its use in plant cultivation. The solutions offered in solving these problems are the introduction of appropriate technology in the supply of F0-F2 mushroom seeds, the introduction of technology transfer goods, the management of baglog waste into compost and the use of compost from baglog waste as organic fertilizer for plant cultivation. The results of the community service that have been achieved are the introduction of technology transfer goods in the form of an autoclave, simple laminar air flow and tools for providing F0-F2 seedlings, training and assistance in providing F0-F2 mushroom seedling, training and assistance in making compost from baglog mushroom waste, direct practice of using mushroom compost for cultivating mung bean crop.

Quantitative Evaluation of the Transmission and Removal of Harmful Smoke Particles in the Operating Room: Full-Scale Experimental and Numerical Study

A large amount of surgical smoke in electrosurgery seriously deteriorates the clean environment of the operating room and can potentially harm medical staff and patients. Exploring the distribution and removal of indoor particulate matter and selecting efficient ventilation patterns are effective ways to control harmful smoke. Therefore, in this study, we combined simulations and full-scale experiments to quantitatively explore the high-concentration spatial regions of particles and compared three ventilation patterns: vertical laminar airflow (VLAF), horizontal laminar airflow (HLAF), and hybrid ventilation, wherein unidirectional airflow (UDAF) was applied to the operating table along with peripheral mixing (UDAF + mixing). We found that simple laminar flow ventilation was significantly affected by the equipment layout and air change rate (air changes per hour; ACH), and the smoke particles were distributed in large amounts in the operating area and could not be removed completely. Conversely, hybrid ventilation can work effectively, and the optimal ACH is approximately 60, which can remove nearly 72% of smoke particles. The airflow distribution in the operating room is also an important factor affecting the distribution and removal of smoke particles. Therefore, medical staff should avoid prolonged exposure to areas with high particle concentrations and particle removal paths.

Partitioning Waves and Eddies in Stably Stratified Turbulence

We consider the separation of motion related to internal gravity waves and eddy dynamics in stably stratified flows obtained by direct numerical simulations. The waves’ dispersion relation links their angle of propagation to the vertical θ , to their frequency ω , so that two methods are used for characterizing wave-related motion: (a) the concentration of kinetic energy density in the ( θ , ω ) map along the dispersion relation curve; and (b) a direct computation of two-point two-time velocity correlations via a four-dimensional Fourier transform, permitting to extract wave-related space-time coherence. The second method is more computationally demanding than the first. In canonical flows with linear kinematics produced by space-localized harmonic forcing, we observe the pattern of the waves in physical space and the corresponding concentration curve of energy in the ( θ , ω ) plane. We show from a simple laminar flow that the curve characterizing the presence of waves is distorted differently in the presence of a background convective mean velocity, either uniform or varying in space, and also when the forcing source is moving. By generalizing the observation from laminar flow to turbulent flow, this permits categorizing the energy concentration pattern of the waves in complex flows, thus enabling the identification of wave-related motion in a general turbulent flow with stable stratification. The advanced method (b) is finally used to compute the wave-eddy partition in the velocity–buoyancy fields of direct numerical simulations of stably stratified turbulence. In particular, we use this splitting in statistics as varied as horizontal and vertical kinetic energy, as well as two-point velocity and buoyancy spectra.

Large-Eddy Simulations of Flow in the FDA Benchmark Nozzle Geometry to Predict Hemolysis.

Modeling of hemolysis due to fluid stresses faces significant methodological challenges, particularly in geometries with turbulence or complex flow patterns. It is currently unclear how existing phenomenological blood-damage models based on laminar viscous stresses can be implemented into turbulent computational fluid dynamics simulations. The aim of this work is to generalize the existing laminar models to turbulent flows based on first principles, and validate this generalization with existing experimental data. A novel analytical and numerical framework for the simulation of flow-induced hemolysis based on the intermittency-corrected turbulent viscous shear stress (ICTVSS) is introduced. The proposed large-eddy simulation framework is able to seamlessly transition from laminar to turbulent conditions in a single flow domain by linking laminar shear stresses to dissipation of mechanical energy, accounting for intermittency in turbulent dissipation, and relying on existing power-law hemolysis models. Simulations are run to reproduce previously published hemolysis data with bovine blood in a benchmark geometry. Two sets of experimental data are relied upon to tune power-law parameters and justify that tuning. The first presents hemolysis measurements in a simple laminar flow, and the second is hemolysis in turbulent flow through the FDA benchmark nozzle. Validation is performed by simulation of blood injected into a turbulent jet of phosphate-buffered saline, with modifications made to account for the local concentration of blood. Hemolysis predictions are found to be very sensitive to power-law parameters in the turbulent case, though a set of parameters is presented that both matches the turbulent data and is well-justified by the laminar data. The model is shown to be able to predict the general behavior of hemolysis in a second turbulent case. Results suggest that wall shear may play a dominant role in most cases. The ICTVSS framework of generalizing laminar power-law models to turbulent flows shows promise, but would benefit from further numerical validation and carefully designed experiments.

Field-emission plasma enhancement of H2–O2 micro-combustion

A detailed three-dimensional computational model is developed to assess the potential of micron-scale field emission dielectric barrier discharge (FE-DBD) plasma actuators in non-premixed microburners with channel heights in the range of Lz = 0.25–0.75 mm. Results for H2–O2 combustion with Reynolds number Re = 100 are studied for different configurations of plasma actuator arrays. Without plasma actuation, results agree with corresponding experiments, although in this case the burner typically suffers from incomplete combustion due to thermal quenching, radical quenching, and slow diffusive mixing. For the range of conditions simulated, plasma actuation increases combustion completeness from 25%–70% to 40%–80% by enhancing mixing, generating radicals, and Joule heating. Ionic wind resulting from the FE-DBD plasma disrupts the otherwise simple laminar flow in the burner, accelerating the growth of a mixing layer and enhancing heat transfer to channel walls. The larger, lower temperature flames reduce thermal gradients (and thereby thermal stresses) in the walls. Radical generation due to electron-impact dissociation extends the reaction zone in the diffusion flame and increases combustion completeness. In all cases, the additional heat release with plasma actuation (100–190 W) is significantly larger than the power needed to sustain the plasma (≲0.1 W), suggesting that plasma actuation may provide a significant advantage in energy generation using realistic portable micro-combustion devices.

Lattice Boltzmann method and channel flow

Lattice Boltzmann methods are presented at an introductory level with a focus on fairly simple simulations that can be used to test and illustrate the model’s capabilities. Two scenarios are presented. The first is a simple laminar flow in a straight channel driven by a pressure gradient (Poiseuille flow). The second is a more complex, including a wedge where Moffatt vortices may be induced if the wedge is deep enough. Simulations of the Poiseuille flow scenario accurately capture the theoretical velocity profile. The experiment shows the location of the fluid-wall boundary and the effects viscosity has on the velocity and convergence time. The numerical capabilities of the lattice Boltzmann model are tested further by simulating the more complex Moffatt vortex scenario. The method reproduces with high accuracy the theoretical predction that Moffat vortices will not form in a wedge if the vertex angle exceeds 146°. Practical issues limitations of the lattice Boltzmann method are discussed. In particular the accuracy of the bounce-back boundary condition is first order dependent on the grid resolution.

The mechanics of a glacier snout

AbstractMeasurements made on a temperate glacier within 200 m of its wedge-shaped terminus cannot be interpreted as simple laminar flow. Instead they are fully explained by a model based on the nonlinear (n ≈ 3) Glen flow law that superposes longitudinal strain rate and simple shearing.

Crossover to surface flow in supercooled unentangled polymer films

We study the driven flow of an unentangled glassy polymer film with a free upper surface and supported below by a substrate using nonequilibrium molecular dynamics simulations based on a bead-spring model. Above the glass transition temperature T(g), simple Poiseuille laminar flow is observed with the film mobility defined as the flow current density per unit pressure gradient scaling as h(3) with the film thickness h. Below T(g), the film mobility becomes independent of h, signifying surface transport. This is in full agreement with recent experiments on the time evolution of capillary waves in polystyrene films supported by silica. A mobile layer is found responsible for the surface transport, as previously conjectured. Our result also shows that it has a velocity profile decaying exponentially into the bulk.

Dissolution of Weak Acids Under Laminar Flow and Rotating Disk Hydrodynamic Conditions: Application of a Comprehensive Convection–Diffusion–Migration–Reaction Transport Model

A steady-state mass transfer model that incorporates convection, diffusion, ionic migration, and ionization reaction processes was extended to describe the dissolution of weak acids under laminar flow and a rotating disk hydrodynamics. The model accurately predicted the experimental dissolution rates of benzoic acid, 2-naphthoic acid, and naproxen in unbuffered and monoprotic buffers within the physiological pH range for both hydrodynamic systems. Simulations at various flow rates indicated a cube root dependency of dissolution rate on the flow rate for a given bulk pH value for the laminar hydrodynamic system, as proposed earlier by Shah and Nelson (1975. J Pharm Sci 64(9):1518-1520) for neutral compounds. The model has limitations in its ability to accurately predict the dissolution of weak acids under certain conditions that imposed steep concentration gradients, such as high pH values, and for polyprotic buffer systems that caused the numerical solution to be unstable, suggesting that alternative numerical techniques may be required to obtain a stable numerical solution at all conditions. The model presents many advantages, most notably the ability to successfully predict the complex process under physiological conditions without simplifying assumptions, and therefore accurately representing the system in a comprehensive manner.

Species-specific effects of fluid shear on grazing by sea urchin larvae: comparison of experimental results with encounter-model predictions

Small-scale turbulence can alter the rate of plankton predator–prey encounters. Encounter models predict that prey ingestion by slow-swimming zooplankton is enhanced at low levels of turbulence. We investigated whether small-scale turbulence increases ingestion for the slow-swimming, suspension-feeding pluteus larvae of the white urchin Lytechinus pictus and the purple urchin Strongylocentrotus purpuratus. Model predictions of the critical level of turbulence, ecr, above which encounters due to turbulence are greater than those due to behavior (swimming or suspension feeding) alone, were experimentally tested using shortand long-term grazing treatments. Because urchin larvae are smaller than the smallest eddy scales of turbulence and thus experience turbulence as laminar shear, larvae were exposed to flow conditions using a simple laminar shear flow with dissipation rates, e, of 0, 0.1, 0.4, and 1 cm2 s–3. Short-term ingestion of beads by L. pictus larvae was unaffected by e < 1 cm2 s–3 but was 30% greater at this level, which was greater than ecr based on flow speeds produced in suspension feeding. Long-term flow treatments with algal prey had no significant effect on grazing or growth. Short-term ingestion of beads by S. purpuratus larvae was unaffected by e < ecr based on suspension feeding; the effect of long-term flow exposure on ingestion and growth could not be investigated because of high mortality, suggesting greater sensitivity to flow exposure compared to L. pictus. Experimental results are consistent with model predictions that ecr is high, and thus levels of turbulence in the ocean are not expected to significantly increase ingestion and reduce food limitation in suspension-feeding urchin larvae.

Anatomy, pathology, and physiology of the tracheobronchial tree: Emphasis on the distal airways

This article covers the airway tree with respect to anatomy, pathology, and physiology. The anatomic portion discusses various primate groups so as to help investigators understand similarities and differences between animal models. An emphasis is on distal airway findings. The pathology section focuses on the inflammatory responses that occur in proximal and distal airways. The physiologic review brings together the anatomic and pathologic components to the functional state and proposes ways to evaluate the small airways in patients with asthma.

Identification of Pollution Sources in Urban Areas Using Reverse Simulation with Reversed Time Marching Method

The present research introduces a technique to determine the location of pollution sources in urban areas through the use of inverse CFD modeling. The technique depends primarily on the solution of the transport equation with time integration in the negative direction. This is called the Reversed Time Marching Method (RTMM). In order to examine the accuracy of RTMM in identifying pollution sources, two examples were given. In the first one, a simple laminar flow was considered and a pollutant was emitted for variable wind conditions. In the second example, the wind flow around a single building was investigated for two different sources. Steady-state numerical simulations were carried out at first in order to estimate flow fields. Then, forward-time simulation was used to calculate pollutant concentrations. In the last stage, the scalar transport equation was solved again but with a reversed flow field and negative diffusion term. By using peak concentration, one could identify the source of the pollution. Results of the study demonstrated that RTMM can identify pollution sources in urban areas with a satisfactory degree of accuracy. However, more work is needed to decrease the wide spread of the concentration field around source location to facilitates the source identification.

Galerkin method for feedback controlled Rayleigh–Bénard convection**This paper is published as part of a collection in honour of Todd Dupont's 65th birthday.

The problem of feedback controlled Rayleigh–Bénard convection is considered. For this problem with the simple flow structure in the vertical direction, a Galerkin method that uses only a few basis functions in this direction is presented. This approximation yields considerable simplification of the problem, explicitly incorporates the non-classical boundary conditions at the horizontal boundaries of the fluid layer resulting from feedback control and reduces the dimension of the original problem by one. This method is in spirit very similar to lubrication theory, where the simple laminar flow in the vertical direction is integrated out across the height of the fluid layer.Using a minimal set of appropriate basis functions to capture the nonlinear behaviour of the flow, we investigate the effects of feedback control on amplitude, wavelength and selection of patterns via weakly nonlinear analysis and numerical simulations of the resulting dimension-reduced problems in two and three dimensions.In the second part of this study we discuss the derivation of the appropriate basis functions and prove convergence of the Galerkin scheme.

A theoretical analysis of the resolution due to diffusion and size dispersion of particles in deterministic lateral displacement devices

We present a model including diffusion and particle-size dispersion for the separation of particles in deterministic lateral displacement devices also known as bumper arrays. We determine the upper critical diameter for diffusion-dominated motion and the lower critical diameter for pure convection-induced displacement. Application of our model to data suggests that the systematic deviation, observed for small particles in several experiments, from the critical diameter for separation given by simple laminar flow considerations may be explained by diffusion and size dispersion.

A comparison of the measured and predicted flowfield in a patient-specific model of an abdominal aortic aneurysm

Numerical simulation is increasingly being used to predict the flowfield within patient-specific geometries of abdominal aortic aneurysms under physiologically realistic flow conditions. This paper reports on a comparison between the flowfield measured in vitro within a patient-specific model of a mature abdominal aortic aneurysm and that predicted using computational fluid dynamics (CFD). Visualization and traverses of axial velocity were obtained at a number of locations in the aneurysm region under both steady and physiologically realistic pulsatile flow conditions. Comparisons between the measured and predicted flowfield show good agreement throughout the aneurysm. Although turbulence was observed distal in the aneurysm during late diastole, best agreement was achieved using a simple laminar flow model.

Rapid solidification and metallic glass formation – Experimental and theoretical limits

Most of the metallic glasses which have been identified to date require rapid solidification processing (RSP) in order to obtain the high cooling rates required to avoid the thermally activated decomposition reactions that result in the formation of crystalline phases. While the free-jet melt spinning technique is commonly used for the investigation of amorphous alloy formation, many of the key process parameters remain poorly understood. In the work presented here, we utilize high speed digital imaging to investigate various melt-pool characteristics and their influence on the melt-spun ribbon. With detailed measurements of melt-pool geometry and surface temperature, we show that the length of this molten zone establishes a critical length scale which characterizes the ribbon thickness and cooling rate. Within certain limits, the ribbon thickness is shown to correlate with a simple 2D laminar flow boundary layer formed at the base of the melt-pool. Estimates of initial quench rate, based on surface temperature measurements, clearly reveal the importance of two distinct cooling periods. The first is the wheel-contact period, where the ribbon remains in intimate contact with the quench wheel and cooling is primarily governed by the heat conduction across the ribbon-wheel boundary. The second is the free-flight period, where the ribbon separates from the wheel, and cooling is governed by radiation and convection into the chamber.

Endothelial Mechanisms of Flow-Mediated Athero-Protection and Susceptibility

See related article, pages 97–105 The arterial endothelium survives remarkably well as the interface between blood and vessel wall in an environment of constantly changing biomechanical stresses as well as acute and chronic exposure to inflammatory stimulants (eg, cytokines and hypercholesterolemia respectively).1 Cell turnover, which tends to occur in regional clusters,2 is otherwise very low in this monolayer. The endothelium also plays an important regulatory role in the pathogenesis of vascular disease. The cells readily respond to diverse stimuli through a repertoire of mechanisms to enhance their own survival even as they facilitate inflammatory, proatherogenic responses in the subendothelial tissue. The necessity to be a responsive cellular interface probably accounts for much of the endothelial phenotype heterogeneity that exists between vascular beds as well as within discrete regions of the arterial circulation.3,4 Hemodynamic characteristics that vary with blood vessel geometry predict the location of arterial sites that are susceptible to atherosclerosis.5 Curved and branching vessel geometries create sites of flow separation that contain transient flow reversals, lower average shear stresses, and occasional turbulence, (collectively, disturbed flow) and that are predictive of lesion formation. In contrast, pulsatile unidirectional laminar flow (and higher average shear stresses) is associated with regions where atherosclerosis rarely occurs, despite there being equivalent exposure to plasma risk factors such as hypercholesterolemia throughout the circulation. Although the signatures of endothelial phenotype in such regions in vivo are varied and complex, data are emerging from genomic5–7 and protein8 analyses of endothelium at such sites that identify molecular differences. Some of these are accessible for study in vitro to investigate detailed mechanisms under more controlled conditions. …

A fluid dynamics approach to bioreactor design for cell and tissue culture

The problem of controlling cylindrical tank bioreactor conditions for cell and tissue culture purposes has been considered from a flow dynamics perspective. Simple laminar flows in the vortex breakdown region are proposed as being a suitable alternative to turbulent spinner flask flows and horizontally oriented rotational flows. Vortex breakdown flows have been measured using three-dimensional Stereoscopic particle image velocimetry, and non-dimensionalized velocity and stress distributions are presented. Regions of locally high principal stress occur in the vicinity of the impeller and the lower sidewall. Topological changes in the vortex breakdown region caused by an increase in Reynolds number are reflected in a redistribution of the peak stress regions. The inclusion of submerged scaffold models adds complexity to the flow, although vortex breakdown may still occur. Relatively large stresses occur along the edge of disks jutting into the boundary of the vortex breakdown region.