Fluid Phenomena Research Articles

VISCOELASTIC PROPERTIES OF FERROFLUIDS WITH CLUSTERED PARTICLES

Clustered (multi-core) magnetic fluids provoke a considerable interest of researchers and practitioners, because they are very promising for various technical and biomedical applications. These fluids contain clusters (clustered particles), which, in turn, consist of ferromagnetic nanoparticles retained together by a polymer shell. The typical size of a cluster varies from a few tens to several hundreds of nanometers, while the sizes of individual single-domain ferroparticles of which it is composed vary from 5 to 12 nm. The rheological phenomena in such fluids (strong magnetorheological effect and slow viscoelastic relaxation) are predetermined by the association of the clustered particles under the action of an external magnetic field into heterogeneous structures and aggregates and the dynamics and disruption of these aggregates in macroscopic deformational flows. In this work, we propose a theoretical model for viscoelastic effects in clustered magnetic fluids. The model is based on the idea of aggregating composite particles into linear chain-like aggregates. In the order of magnitude, the theoretical results agree with experimental data.

考虑压裂液渗吸的压后压裂液返排的数值模拟

Fracturing fluid flowback is a key step in the process of hydraulic fracturing, and the imbibition of fracturing fluid in unconventional tight reservoirs cannot be ignored. Based on the oil-water two-phase seepage theory, Bernoulli equation and the continuity equation, we establish a numerical simulation model of post-fracturing flowback by considering the effect of fracturing fluid imbibition and obtain the pressure and flowback rate during the flowback process through programmed numerical calculation. The critical flow rate of fracturing fluid when the proppant starts to reflux is calculated according to the proppant backflow model. Then an optimization design method of flowback working system is formed based on the principle of controlling proppant backflow and rapid fluid flowback. The numerical simulation results are compared with the actual flowback data of LX3 well, and the flowback working strategy of M87 well is designed, and the effects of formation fluid viscosity and initial formation pressure on fracturing fluid flowback are analyzed. The results show that a phenomenon of formation fluid seepage to fractures is observed during the flowback, and the change of original formation pressure has a significant impact on fracturing fluid flowback, but the formation produced fluid has minor effects. The numerical results of flowrate and wellhead pressure of LX3 well are consistent with the field monitor data, with average errors of 13.8% and 15.5% respectively. It is verified that the flowback numerical model has high accuracy and can be used to guide the on-site fracturing flowback construction design in oilfield.

The screeching jet, seen from all sides

Shock-containing supersonic jets undergoing resonance processes are challenging from both a measurement and simulation perspective. These jets are host to a broad range of complex fluid phenomena: intense acoustic waves, turbulence, wavepackets and strong shock waves. Strong shocks present a challenge to both the experimental and numerical researcher. In the paper of Léon et al. (J. Fluid Mech., vol. 947, 2022, A36), a novel optical technique based on multi-axis digital holographic interferometry is applied to the study of a highly underexpanded screeching jet, producing density measurements of unprecedented clarity and resolution. Where prior studies have been restricted to extrapolating the three-dimensional field from two-dimensional slices or projections, in this work the authors directly measure the three-dimensional helical structure of the wavepacket associated with jet screech.

Using mesoporous thin films as nano-micro-fluidic tools

Achieving active control on small amounts of liquids represents a substantial challenge in both scientific and engineering aspects. Imbibition of fluids in bodies with nanoscale dimensions enables the spontaneous propelling of nano-flows because of the powerful capillarity at small-length scales. Peculiarities of nanopore imbibition at the thin film level lead to distinctive capillary transport phenomena of fluids across the nanopore matrix. This particular imbibition also impacts on the behavior of the in-contact liquid micro-volumes. These both features add versatile alternatives to the high interest in the management of femtolitre to microlitres amounts of liquids. Herein, we show a brief discussion-outlook based on recent advances in the design of versatile tools to attain programmable nano/microfluidics using mesoporous thin film platforms. Cited as: Berli, C. L. A., Bellino, M. G. Using mesoporous thin films as nano-micro-fluidic tools. Capillarity, 2022, 5(6): 123-127. https://doi.org/10.46690/capi.2022.06.03

Depictions of fluid phenomena in art

Artists spent a great deal of time studying anatomy for precise rendering of the human body as well as light, shadows, and perspective for convincing representation of the three-dimensional world. But in many paintings, they also had to depict fluids in their static and dynamic states -- a subject they could not study thoroughly, which led to a number of glaring misrepresentations or deliberate deceits.

Variational multiscale reinforcement learning for discovering reduced order closure models of nonlinear spatiotemporal transport systems

A central challenge in the computational modeling and simulation of a multitude of science applications is to achieve robust and accurate closures for their coarse-grained representations due to underlying highly nonlinear multiscale interactions. These closure models are common in many nonlinear spatiotemporal systems to account for losses due to reduced order representations, including many transport phenomena in fluids. Previous data-driven closure modeling efforts have mostly focused on supervised learning approaches using high fidelity simulation data. On the other hand, reinforcement learning (RL) is a powerful yet relatively uncharted method in spatiotemporally extended systems. In this study, we put forth a modular dynamic closure modeling and discovery framework to stabilize the Galerkin projection based reduced order models that may arise in many nonlinear spatiotemporal dynamical systems with quadratic nonlinearity. However, a key element in creating a robust RL agent is to introduce a feasible reward function, which can be constituted of any difference metrics between the RL model and high fidelity simulation data. First, we introduce a multi-modal RL to discover mode-dependant closure policies that utilize the high fidelity data in rewarding our RL agent. We then formulate a variational multiscale RL (VMRL) approach to discover closure models without requiring access to the high fidelity data in designing the reward function. Specifically, our chief innovation is to leverage variational multiscale formalism to quantify the difference between modal interactions in Galerkin systems. Our results in simulating the viscous Burgers equation indicate that the proposed VMRL method leads to robust and accurate closure parameterizations, and it may potentially be used to discover scale-aware closure models for complex dynamical systems.

Electro-elastic instability in electroosmotic flows of viscoelastic fluids through a model porous system

Electrokinetic transport phenomena in porous media are encountered in many practical applications such as electro-chromatography, micro-pumping, chemical remediation of contaminated soil, etc. These applications often deal with various complex viscoelastic fluids (such as polymers, emulsions, suspensions, different kinds of biofluids, etc.) along with simple Newtonian ones. This study presents a detailed numerical investigation on this electrokinetic transport of both Newtonian and viscoelastic fluids in a model porous system consisting of a long micropore with step expansion and contraction. Over the whole range of conditions encompassed in this study, a steady and symmetric flow field is observed for a Newtonian fluid. However, for a viscoelastic fluid, we observe a transition in the flow field from steady and symmetric to unsteady and asymmetric once the Weissenberg number (ratio of the elastic to that of the viscous forces) exceeds a critical value. We show that this transition is caused due to the onset of an electro-elastic instability in the system. The critical value of this Weissenberg number (at which this transition occurs) depends on various factors. In particular, we find that this value increases with the polymer viscosity ratio and expansion and contraction lengths of the micropore. At fixed values of the electric field strength, polymer viscosity ratio, contraction and expansion lengths of the micropore, we observe the existence of different vortex dynamics within this model porous system as the Weissenberg number gradually increases, such as the emergence of the entrant and re-entrant lip vortices, oscillating lip vortices, multi vortices, etc. Therefore, the electrokinetic flow dynamics of viscoelastic fluids in a porous system is much more complex than that of simple Newtonian fluids. We hope this study for a model porous system would facilitate a better understanding of the electrokinetic transport phenomena of viscoelastic fluids in an actual porous media. Furthermore, we show how this model system of a long micropore with step expansion and contraction could also be successfully utilized for other practical applications such as mixing two viscoelastic fluids.

Entropy analysis of unsteady magnetohydrodynamic thin liquid film flow of Maxwell nanofluids with variable fluid properties

The flow and heat transfer phenomena of a viscous fluid in a thin film over an expanding flat surface possesses optimistic applications in a large number of technological processes. Heat and mass transfer rate within the thin film bears an unequivocal factors on the performance of coating process and the chemical nature of the product. This article concerns with the study of unsteady boundary layer magnetohydrodynamic thin film flow of Maxwell nanofluid past over an exponentially stretching surface subject to slip effect on velocity and suction/injection at the boundary. The heat transfer mechanism is influenced by the thermal radiation, temperature dependent thermal conductivity, viscous dissipation of energy and a non-uniform heat source/sink. We have analyzed the entropy generation of the system by paying due attention to the variable fluid properties and film thickness. The system of arising time dependent coupled nonlinear partial differential equations governing the fluid flow are converted into a system of ordinary differential equation by utilizing suitable self-similar transformations. The reduced two-point boundary value problem is then solved with the aid of well known Runge–Kutta–Fehlberg integration technique based shooting method. The mathematical model suggests an extra kinematic boundary condition which is utilized to compute the thickness of the thin film by employing the Newton–Raphson method. The investigation highlights that the arising controlling parameters such as magnetic parameter, radiation parameter, viscosity parameter, thermal conductivity parameter have strong effect on velocity field, temperature field, Nusselt number, and the thickness of the thin film. Moreover, the Bejan number, a measure of thermal irreversibility, is highly affected by the variation of the magnetic field strength, thermal radiation, dissipation of energy, thermal conductivity parameter, viscosity parameter and heat source/sink.

Deep-learning prediction and uncertainty quantification for scramjet intake flowfields

Scramjet is a promising propulsion technology that provides efficient and flexible access-to-space and high-speed point-to-point transportation. Since the design process of scramjet (supersonic combustion ramjet) engines requires numerous flowfield evaluations, fast and accurate flow predictions play a key role in promoting the development of knowledge and technologies. Deep learning techniques are increasingly used for flow prediction, and the present study applies them to viscous supersonic flowfields inside scramjet intakes. The capability and limitations of deep learning prediction for such flowfields have been investigated from the viewpoints of both physics and machine learning by means of uncertainty quantification and principal component analysis. The results indicate that the flowfields with complex aerodynamic phenomena such as boundary layer separation and Mach disks are difficult to predict. It has been attributed to lack of similar flowfields as well as the sensitivity of the fluid phenomena to the geometries. Uncertainty quantification effectively allows for the detection of such difficult cases without model verification prior to utilization. It has been further employed to address the issues in the prediction of flowfields with boundary-layer separations by increasing the number of training data effectively.

Italian Diasporic Studies: The Then and Now

Italian Diasporic Studies: The Then and Now

Interstitial Fluid Flows along Perivascular and Adventitial Clearances around Neurovascular Bundles.

This study reports new phenomena of the interstitial fluid (ISF) microflow along perivascular and adventitial clearances (PAC) around neurovascular bundles. The fluorescent tracing was used to observe the ISF flow along the PAC of neurovascular bundles in 8-10 week old BALB/c mice. The new results include: (1) the topologic structure of the PAC around the neurovascular bundles is revealed; (2) the heart-orientated ISF flow along the PAC is observed; (3) the double-belt ISF flow along the venous adventitial clearance of the PAC is recorded; (4) the waterfall-like ISF flow induced by the small branching vessel or torn fascia along the PAC is discovered. Based on the above new phenomena, this paper approached the following objectives: (1) the kinematic laws of the ISF flow along the PAC around neurovascular bundles are set up; (2) the applicability of the hypothesis on the PAC and its subspaces by numerical simulations are examined. The findings of this paper not only enriched the image of the ISF flow through the body but also explained the kernel structure of the ISF flow (i.e., the PAC). It helps to lay the foundation for the kinematics and dynamics of the ISF flow along the PAC around neurovascular bundles.

Feelings and the acceptance spectrum in adult stuttering

Purpose: The purpose of this exploratory study was to describe the feelings about and attitudes toward stuttering expressed in the narrative responses of a large sample of adults who stutter. Method: Eighty-eight adults who stutter answered an online survey questionnaire on their feelings about their stuttering. Thematic analysis was conducted to investigate the individual nuances of each participant’s response, which gave rise to general themes across the sample. Results: Five major themes emerged from participants’ responses regarding their feelings about their stuttering: (I) negative feelings about stuttering; (II) negative attitudes toward stuttering; (III) negative impact on quality of life; (IV) the acceptance spectrum; and (V) exclusively positive feelings and attitudes about stuttering. Negative feelings included embarrassment and shame, frustration, and grief, while negative attitudes were hatred, dislike, and annoyance. Stuttering’s negative impact on participants’ lives in general as well as on specific aspects such as job interviews were described. Participants reported varying degrees of acceptance, highlighting that acceptance is not an ‘all or nothing’ phenomenon. Examples of positive feelings were confidence and comfort. Conclusion: The vast majority of participants included negatively charged elements in their responses, and acceptance was largely described as being a fluid phenomenon, regardless of participants’ ages. Findings indicate clinical implications for addressing feelings, attitudes, and acceptance across the lifespan.

Analysis of chaos-coherence peculiarities within the chaotic phenomena of fluid at finite temperature

In this distinctive research, I explored the influence of temperature and momentum-dependent coherence and chaos radiations on particles emanated fluid with quantum correlations. The equations are elucidated by using the interferometry technique to prevail in perspicuous aphorism for the coherence-chaotic field. Chaotic parameter examines the coherence through boson femtoscopy within an evolving boson gas model and probes significant parameters within the produced fluid characterization for the potential of harmonics oscillators. The proportion of condensate of identical bosons, densities distribution, and the correlations functions for the expansion of boson gas are investigated. The findings suggest that the particular temperatures in the relativistic smashing possess the hadronic phase and the resulting sources at that phase containing hundreds of analogous boson particles divulge the robustness of quantum coherence. The correlations are delineated to analyze the coherence and source peculiarities with certain temperature ranges, particles number, and particle pairs averaging momentum. At small pair momenta, the finite condensation reduces the correlations in pion interferometry observations and strives for an insignificant effect at high particles pair momenta. As shown in the plots the graphical interpretations of the density distribution, correlations and chaotic profile against assorted apropos parameters have been demonstrated for pertinent physical reasons. The significant results divulged that the density distributions possession enhance at higher coherent emission and lower temperature regimes. Such findings reveal the lucrativeness in the field of engineering applications.

Collective phenomena in a quasi-classical electron fluid within the interpolational self-consistent method of moments

Collective processes in a quasi-classical electron gas are investigated within the framework of the interpolational self-consistent method of moments, which makes it possible to express the dispersion and decrement of plasma waves, and the dynamic structural factor of the system exclusively in terms of its static structural factor so that five sum rules are satisfied automatically. Different models are used of the static structure factor; the stability and robustness of the results of the moment approach taking into account the accuracy of these models is confirmed and tested by comparison to the alternative molecular dynamics simulation data.

Micro- and Nanoscale Imaging of Fluids in Water Using Refractive-Index-Matched Materials.

Three-dimensional (3D) visualization in water is a technique that, in addition to macroscale visualization, enables micro- and nanoscale visualization via a microfabrication technique, which is particularly important in the study of biological systems. This review paper introduces micro- and nanoscale 3D fluid visualization methods. First, we introduce a specific holographic fluid measurement method that can visualize three-dimensional fluid phenomena; we introduce the basic principles and survey both the initial and latest related research. We also present a method of combining this technique with refractive-index-matched materials. Second, we outline the TIRF method, which is a method for nanoscale fluid measurements, and introduce measurement examples in combination with imprinted materials. In particular, refractive-index-matched materials are unaffected by diffraction at the nanoscale, but the key is to create nanoscale shapes. The two visualization methods reviewed here can also be used for other fluid measurements; however, because these methods can used in combination with refractive-index-matched materials in water, they are expected to be applied to experimental measurements of biological systems.

On a hybrid continuum-kinetic model for complex fluids

In the present work, we first introduce a general framework for modelling complex multiscale fluids and then focus on the derivation and analysis of a new hybrid continuum-kinetic model. In particular, we combine conservation of mass and momentum for an isentropic macroscopic model with a kinetic representation of the microscopic behavior. After introducing a small scale of interest, we compute the complex stress tensor by means of the Irving-Kirkwood formula. The latter requires an expansion of the kinetic distribution around an equilibrium state and a successive homogenization over the fast in time and small in space scale dynamics. For a new hybrid continuum-kinetic model the results of linear stability analysis indicate a conditional stability in the relevant low speed regimes and linear instability for high speed regimes for higher modes. Extensive numerical experiments confirm that the proposed multiscale model can reflect new phenomena of complex fluids not being present in standard Newtonian fluids. Consequently, the proposed general technique can be successfully used to derive new interesting systems combining the macro and micro structure of a given physical problem.

Electrokinetics in antimicrobial resistance analysis: A review.

Infections caused by antimicrobial resistance are a serious problem in the world. Currently, commercial devices for antimicrobial susceptibility testing and resistant bacteria identification are time-consuming. There is an urgent need to develop fast and accurate methods, especially in the process of sample pretreatment. Electrokinetic (EK) is a family of electric-field-based kinetic phenomena of fluid or embedded objects, and EK applications have been found in various fields. In this paper, EK bacteria manipulation, including enrichment and separation, is reviewed. Focus is given to the rapid electric-based minimum inhibitory concentration measurement. The future directions and major challenges in this field are also outlined.

Defining fascist pluralism's role in the development of modernity

In the sphere of politics, particularly in the area of governance, fascism is a fluid and undefined phenomenon whose nature, despite the best efforts of theorists and philosophers in the political and social sciences, remains shrouded in mystery. In a metaphor, populism is like a mirror room where every essence that is put in it gets lost among thousands of other images of a similar kind. This confusion is the point that fascist aspires to get at among various socioeconomic strata. In order to determine which political component or components fascism, with such a fluid nature, seeks to achieve, we attempt to provide general results from the origins of fascism; its characteristics and patterns of behavior, especially in the field of pluralism and how it treats modernity, by providing explanations of fascism research. In a way, the goal of this paper is to explore, clarify, and show how to use the markers of modernity and the relationship between fascist institutions. This article used a descriptive-analytical research design to discuss the topic using an interpretive-critical framework. This article's study is based on a methodical approach using the terms "fascism" and "modernity."

Explaining the Relationship between Fascist Pluralism and Modernity

Fascism is a fluid and unknown phenomenon in the world of politics and especially in the field of governance, a phenomenon whose nature; despite all the efforts of theorists and thinkers in the field of political and social sciences, remains in an aura of ambiguity. Fascism is like a mirror room in allegory, every essence that is placed in it is lost in thousands of images of its kind and this confusion is the same populism that the idea of fascism seeks in different social strata as its destination. In this article, we try to provide general results from the origins of fascism; its characteristics and patterns of behavior, especially in the field of pluralism and how it treats modernity, by providing explanations of fascism research, to finally find out which political component or components fascism with such a fluid nature seeks to achieve. In a sense, the purpose of this article is to investigate and explain the relationship between fascist institutions and modernity and how to use its indicators. The research method of this article is descriptive-analytical which has explained the subject with an interpretive-critical approach. The analysis of this article is based on a systematic method based on the keywords of fascism and modernity.

Cleaning-in-place: Case studies of coupled flows and complex fluids

Many modern food, pharmaceutical and fast moving consumer goods manufacturing facilities clean their process equipment by automated circulation of cleaning solutions through the units. The soiling layers are often non-Newtonian, soft solids while the fluid mechanics are inherently dynamic and involve coupling between the cleaning solution and the soil. This talk will present results from recent studies of the removal of viscoplastic layers from smooth rigid surfaces by coherent, turbulent, impinging water jets, where there is a rich range of fluid phenomena on display. We pose the engineering question: what level of detailed modelling do we require to obtain acceptable predictive capability, and along the way introduce some of the challenges that colleagues might want to look into.