Fluid Phenomena Research Articles

Cytological Analysis of CSF in Patients with Acute Schizophrenia

Cerebrospinal fluid (CSF) analysis is one of the most important tests in the diagnosis of central nervous system (CNS) diseases. Although CSF analysis is most commonly used in neurological pathological conditions, it also has its place in psychiatry. Studies to date have described several valuable specific cytomorphological phenomena in the cerebrospinal fluid of patients with acute schizophrenia, which indicate inflammatory or immune-mediated etiopathogenesis of the disease. Additional and long-term research is needed to confirm and standardize the importance of cytological analysis of cerebrospinal fluid in the diagnosis and etiopathogenesis of acute schizophrenia.

Simulations of the Biermann battery mechanism in two-fluid partially ionised plasmas

Context. In the absence of an initial seed, the Biermann battery term of a non-ideal induction equation acts as a source that generates weak magnetic fields. These fields are then amplified via a dynamo mechanism. The Kelvin-Helmholtz instability is a fluid phenomenon that takes place in many astrophysical scenarios and can trigger the action of the Biermann battery and dynamo processes. Aims. We aim to investigate the effect of the ionisation degree of the plasma and the interaction between the charged and neutral species on the generation and amplification of magnetic fields during the different stages of the instability. Methods. We use the two-fluid model implemented in the numerical code Mancha-2F. We perform 2D simulations starting from a configuration with no initial magnetic field and which is unstable due to a velocity shear. We vary the ionisation degree of the plasma and we analyse the role that the different collisional terms included in the equations of the model play on the evolution of the instability and the generation of magnetic field. Results. We find that when no collisional coupling is considered between the two fluids, the effect of the Biermann battery mechanism does not depend on the ionisation degree. However, when elastic collisions are taken into account, the generation of magnetic field is increased as the ionisation degree is reduced. This behaviour is slightly enhanced if the process of charge-exchange is also considered. We also find a dependence on the total density of the plasma related to the dependence on the coupling degree between the two fluids. As the total density is increased, the results from the two-fluid model converge to the predictions of single-fluid models. Conclusions. The charged-neutral interaction in a partially ionised plasmas has a non-negligible effect on the Biermann battery mechanism and it effectively enhances the generation of a magnetic field. In addition, single-fluid models, which assume a very strong coupling between the two species, may overestimate the contribution of this interaction in comparison with two-fluid models.

Stability and exponential decay for the 2D anisotropic Boussinesq equations with horizontal dissipation

The hydrostatic equilibrium is a prominent topic in fluid dynamics and astrophysics. Understanding the stability of perturbations near the hydrostatic equilibrium of the Boussinesq system helps gain insight into certain weather phenomena. The 2D Boussinesq system focused here is anisotropic and involves only horizontal dissipation and horizontal thermal diffusion. Due to the lack of the vertical dissipation, the stability and precise large-time behavior problem is difficult. When the spatial domain is \({\mathbb {R}}^2\), the stability problem in a Sobolev setting remains open. When the spatial domain is \({\mathbb {T}}\times {\mathbb {R}}\), this paper solves the stability problem and specifies the precise large-time behavior of the perturbation. By decomposing the velocity u and temperature \(\theta \) into the horizontal average \(({\bar{u}}, {\bar{\theta }})\) and the corresponding oscillation \(({\widetilde{u}}, {\widetilde{\theta }})\), and deriving various anisotropic inequalities, we are able to establish the global stability in the Sobolev space \(H^2\). In addition, we prove that the oscillation \(({\widetilde{u}}, {\widetilde{\theta }})\) decays exponentially to zero in \(H^1\) and \((u, \theta )\) converges to \(({\bar{u}}, {\bar{\theta }})\). This result reflects the stratification phenomenon of buoyancy-driven fluids.

Implementation of Stochastic Optimization Method-Assisted Radial Basis Neural Network for Transport Phenomenon in Non-Newtonian Third-Grade Fluids: Assessment of Five Optimization Tools

Implementation of radial basis neural network is demonstrated by considering a test case of non-Newtonian third-grade fluid flow and heat transfer through two parallel plates. Five commonly used stochastic optimization methods: genetic algorithm, global search algorithm, multiple starting point algorithm, simulated annealing algorithm, and pattern search algorithm, are employed to optimize the RBNN. Flow of a non-Newtonian third-grade fluid through two parallel plates, subjected to uniform heat flux, is considered. At first, governing equations, describing the flow and heat transfer problem, are solved by the least-square method, a semi-analytical tool. The velocity and the temperature profiles are obtained for different values of third-grade fluid parameter ‘A’, which are then used for training different stochastic optimization method-assisted RBNNs (SOMARBNNs). For proper functioning of RBNN, a suitable value for an important attribute called ‘spread’ is required. Deciding the value for ‘spread’ requires experience and knowledge of neural networks. The present approach makes the selection of proper value of ‘spread’ very easy, and beginners can use the RBNN for problem-solving. With the help of different stochastic optimization methods, the value of spread for the RBNN is determined. Once all SOMARBNNs are trained, the temperature profile and the corresponding third-grade fluid parameter ‘A’ are obtained as output, corresponding to any new velocity profile fed as input. Further, the data for training are perturbed by different levels of noise, and different SOMARBNNs are successfully employed to get the output. The performance evaluation of different SOMARBNNs is carried out in terms of CPU time and error in result. The results indicate that PSAARBNN is better than other SOMARBNNs, as it is able to generate results with high accuracy for both low noise data and high noise data. Moreover, the CPU time requirement by PSAARBNN is lowest.

Modelling Rayleigh-Bénard convection coupled with electro-vortex flow in liquid metal batteries

Liquid Metal Batteries (LMBs) are a promising grid-scale energy storage technology that offers low costs per kilowatt-hour, high energy and current densities, as well as low fade rates. The all-liquid composition of the batteries, as well as the presence of temperature gradients and electric and magnetic fields, result in the occurrence of multiple fluid phenomena. These can affect the hydrodynamic stability of the battery, thereby making their interactions critical to understand. In this work, the interaction of Rayleigh-Bénard convection and Electro-vortex flow is investigated as these types of flow will be present in Liquid Metal Batteries from laboratory to grid-scale. A single-layer electrode is simulated, and the computed results compared with experimental data from the literature. It was found that Rayleigh-Bénard convection is unsteady in the liquid metal electrode. The introduction of a 2 A current stabilises the convection cells, whilst the introduction of a 40 A current leads to the dominance of Electro-vortex flow at the central region of the electrode. The results in this work match experimental data closer than previously published models offering insight into the interaction between Rayleigh-Bénard convection and Electro-vortex flow in the anodes of discharging Liquid Metal Batteries.

Numerical and theoretical modeling of droplet impact on spherical surfaces

Droplet impact on solid surfaces is a fluid phenomenon widely involved in additive manufacturing, heat management, and coating, in which the ability to exert control over the impact dynamics and duration is critical. While past studies have established a comprehensive understanding of the impact on flat substrates, what we know about the impact dynamics on curved solid surfaces is still limited. This work aims to elucidate the physics of droplet impact on spherical surfaces with different Weber numbers (We), radii (Rs), and surface wettability (θeq) using a combination of axisymmetric lattice Boltzmann method (LBM) and theoretical analysis. The model developed in our previous work [H. N. Dalgamoni and X. Yong, Phys. Rev. E 98, 13102 (2018)] was extended and modified for simulating the normal impact of droplet on curved substrates in the low Weber number regime (i.e., We ≤ 15), in which axisymmetric assumption of droplet deformation holds. The LBM simulations show that We, Rs, and θeq significantly affect the spreading and recoiling of droplet during impact. The parametric studies uncover five outcomes of impact, which range from complete deposition to total rebound. A simulation-predicted phase diagram was constructed and correlated with the total time that the droplet was in contact with the solid. In addition, a theoretical model based on energy budget during impact was developed to predict the rebound threshold for impact on spherical targets when varying We, Rs, and θeq independently, which agrees well with simulation observations. These findings provide fundamental insight into surface structure design for controlling droplet hydrodynamics and the contact time during impact.

Powerful Acoustogeometric Streaming from Dynamic Geometric Nonlinearity.

Past forms of acoustic streaming, named after their progenitors Eckart (1948), Schlichting (1932), and Rayleigh (1884), serve to describe fluid and particle transport phenomena from the macro to micro-scale. Governed by the fluid viscosity, traditional acoustic streaming arises from second-order nonlinear coupling between the fluid's density and particle velocity, with the first-order acoustic wave time averaging to zero. We describe a form of acoustogeometric streaming that has a nonzero first-order contribution. Experimentally discovered in nanochannels of a height commensurate with the viscous penetration depth of the fluid in the channel, it arises from nonlinear interactions between the surrounding channel deformation and the leading order acoustic pressure field, generating flow pressures three orders of magnitude greater than any known acoustically mediated mechanism. It enables the propulsion of fluids against significant Laplace pressure, sufficient to produce 6 mm/s flow in a 130-150nm tall nanoslit. We find quantitative agreement between theory and experiment across a variety of fluids and conditions, and identify the maximum flow rate with a channel height 1.59 times the viscous penetration depth.

Geometric frustration in polygons of polariton condensates creating vortices of varying topological charge

Vorticity is a key ingredient to a broad variety of fluid phenomena, and its quantised version is considered to be the hallmark of superfluidity. Circulating flows that correspond to vortices of a large topological charge, termed giant vortices, are notoriously difficult to realise and even when externally imprinted, they are unstable, breaking into many vortices of a single charge. In spite of many theoretical proposals on the formation and stabilisation of giant vortices in ultra-cold atomic Bose-Einstein condensates and other superfluid systems, their experimental realisation remains elusive. Polariton condensates stand out from other superfluid systems due to their particularly strong interparticle interactions combined with their non-equilibrium nature, and as such provide an alternative testbed for the study of vortices. Here, we non-resonantly excite an odd number of polariton condensates at the vertices of a regular polygon and we observe the formation of a stable discrete vortex state with a large topological charge as a consequence of antibonding frustration between nearest neighbouring condensates.

A partitioned solution approach for the fluid–structure interaction of thin-walled structures and high-Reynolds number flows using RANS and hybrid RANS–LES turbulence models

In this work the partitioned solution approach for the fluid–structure interaction (FSI) of thin-walled structures and high-Reynolds number (Re) flows modeled using Reynolds–Averaged Navier–Stokes (RANS) and hybrid Reynolds–Averaged Navier–Stokes – Large Eddy Simulation (RANS–LES) turbulence models are described. The advanced turbulence modeling is needed to capture very complex fluid phenomena which triggers instabilities of thin–walled structures present in supersonic flow regimes. The finite element (FE) updated Lagrangian formulation (ULF) for the nonlinear elastic solids is used to predict its dynamical behavior. The main contribution addresses to the linear stress–strain relation Laplacian members, which are solved implicitly, on that way decreasing required memory resources and improving solution stability in the same time. The structures of the interest include the vast variety of membranes, curved shells and plates. The instabilities encountering these structures include limit cycle oscillations (LCO), flutter and buckling of the panels. The phenomena appear in everyday engineering practice and a need for the powerful tools to handle such problems is a common goal. Utilization of the unstructured non-regular meshes allows the precise distribution of computational nodes at the physical boundaries of the fluid and solid domains. It is naturally allowing application of the common approach for the fluid–solid interface coupling, as well as classical data interpolation schemes between fluid and solid on the FSI interface. High-Re flows, both 2D (benchmark) and 3D turbulent FSI case are chosen for the validation. Two numerical methods are coupled via a moving boundary treatment, in a staggered way. The proposed coupling method showed a good agreement with the reference test cases. The current FSI framework is developed to serve as a tool for the liquid rocket engine development.

Teaching the incompressible Navier–Stokes equations to fast neural surrogate models in three dimensions

Physically plausible fluid simulations play an important role in modern computer graphics and engineering. However, in order to achieve real-time performance, computational speed needs to be traded-off with physical accuracy. Surrogate fluid models based on neural networks (NN) have the potential to achieve both fast fluid simulations and high physical accuracy. However, these approaches rely on massive amounts of training data, require complex pipelines for training and inference, or do not generalize to new fluid domains. In this work, we present significant extensions to a recently proposed deep learning framework, which addresses the aforementioned challenges in two dimensions (2D). We go from 2D to three dimensions (3D) and propose an efficient architecture to cope with the high demands of 3D grids in terms of memory and computational complexity. Furthermore, we condition the neural fluid model on additional information about the fluid's viscosity and density, which allows for simulating laminar as well as turbulent flows based on the same surrogate model. Our method allows us to train fluid models without requiring fluid simulation data beforehand. Inference is fast and simple, as the fluid model directly maps a fluid state and boundary conditions at a moment t to a subsequent fluid state at t + dt. We obtain real-time fluid simulations on a 128 × 64 × 64 grid that include various fluid phenomena such as the Magnus effect or Kármán vortex streets and generalize to domain geometries not considered during training. Our method indicates strong improvements in terms of accuracy, speed, and generalization capabilities over current 3D NN-based fluid models.

Electromagnetic Variations Associated with Seismic Waves

It is observed that seismic waves generate electromagnetic variations. The excitation mechanisms have been analyzed and formulated by many researchers. Three mechanisms have been mainly considered; stress effects for physical properties of rocks such as the piezoelectricity and the piezomagnetic effects, the electromagnetic induction due to the oscillation in the geomagnetic field, and the electrokinetic phenomena in pore fluids. While the stress effects and the electrokinetic phenomena take place in the crust, the induction process functions in various regions of the earth as the crust, the oceans, and the ionosphere. The characteristics of the electromagnetic signals produced with these mechanisms are also reviewed. It is expected that the electromagnetic signals derived from seismic waves are used to investigate the dynamics and the structures of the earth and planets.

Learning about culture(s) via intercultural digital exchange: opportunities, challenges, and grey areas

ABSTRACT Twenty-six participants aged 12–18 living in four countries were interviewed about their experiences participating in a digital exchange programme and learning about cultures. Abductive analysis of the transcripts suggests that social media-type learning formats offer particular opportunities for young people to: (1) engage with different cultures and feel a sense of connection to people with different cultural affiliations to their own; (2) expand their view of culture as a complex, multifaceted, fluid phenomenon; (3) consider or reconsider their existing understandings of culture(s) in ways that may involve upending stereotypes; and (4) situate their own lives, identities, and values relative to those of other young people and reflect on how they themselves have been influenced by cultural forces. However, educators should also be attentive to the challenges of what we call the ‘Three O’s’ – overgeneralisation, overconfidence, and othering – as well as several grey areas that require skilful and thoughtful navigation.

Fully developed relativistic turbulence

We use a simple model consisting of energy-momentum tensor conservation and a Maxwell-Cattaneo equation for its viscous part to study nonlinear phenomena in a real relativistic fluid. We focus on new types of behavior without nonrelativistic equivalents, such as an entropy cascade driven by fluctuations in the tensor degrees of freedom of the theory. We write down the von K\'arm\'an-Howarth equations for this kind of turbulence, and consider the correlations corresponding to fully developed turbulence.

Numerical Study on the Influence of Supercritical Heat Transfer Deterioration on the Combustion Process

The conjugate heat transfer from in-furnace combustion to in–tube supercritical fluid has been numerically investigated in this study. The mathematical model of the conjugate heat transfer process has been constructed. The effects of the abnormal heat transfer phenomena of supercritical fluid in tube and combustion status change in the furnace on the conjugate heat transfer process were analyzed. The results demonstrate that the Renormalization-group (RNG) model has better prediction ability. The Abe-Kondoh-Nagano (AKN) model will have an over-prediction problem for the abnormal heat transfer. The RNG model is also more accurate in simulating the combustion process in the furnace.

Exhaust temperature control for safe and efficient thermal regeneration of diesel particulate filter

Abstract It is crucial for the diesel particulate filter (DPF) that the exhaust temperature at the DPF inlet is well managed and accurately controlled during the thermal regeneration process, in order to ensure the integrity of the filter and improve regeneration efficiency simultaneously. However, this is challenging because the DPF and the upstream diesel oxidation catalyst are complex systems with complicated chemical, thermal and fluid phenomena, especially in real-world driving where the operation and environment conditions are varying and unpredictable. In some cases when the engine speed is suddenly dropped to idle (DTI) from normal operation conditions, uncontrolled regeneration events may occur and result in excessive temperature spikes inside the DPF that may melt down the filter. The objective of this work is to improve safe, reliable and efficient filter operation during the DPF thermal regeneration process, thus reducing the risk of destructive melting of the DPF. Firstly, an experimental method based on the DTI regeneration tests is investigated under a wide range of operation conditions with different soot load levels and regeneration temperatures. Results indicate that the target regeneration temperature curve can be derived as an empirical function of the amount of soot loading in the DPF, which is essential to ensure regeneration safety of the filter in runtime. Then, a novel control strategy combining a model-based feedforward control law and a feedback control law based on the internal model control approach is proposed and developed. The presented control strategy is finally validated under transient conditions in the real driving cycles. Results show that the temperature overshoot is less than 5% during the initial regeneration control stage and the tracking error remains within ± 15 °C of the target regeneration temperature, which is beneficial to safe and efficient thermal regenerations of the filter.

Numerical Simulation of Radiative MHD Sutterby Nanofluid Flow Through Porous Medium in the Presence of Hall Currents and Electroosmosis

Analysis of thermal and fluid phenomena based on the fluid dynamics theory leads to understanding of fundamental mechanisms in modern technologies. Thermal/fluid transport is critical to many applications, such as photothermal cancer therapy, solar thermal evaporation and polymer composites. The current study focusses to investigate the effect of magnetohydrodynamics, Hall currents and electroosmosis on the propulsion of Sutterby nanofluids in a porous microchannel. The Brownian motion and thermophoresis effects have also been considered. The governing equations for the momentum, temperature and nanoparticle volume fraction have been modified under the suitable non-dimensional quantities. The resulting dimensionless system of equations have been solved using bvp4c package in computational software MATLAB. The pictorial representations have been presented for various flow quantities with respect to sundry fluid parameters. It is noted from the investigation that, there is a decrease in fluid velocity with an increase in Hartmann number, temperature decreases with the increment in radiation parameter and nanoparticle volume fraction reduces with the increment of Prandtl number and thermophoresis parameter. The results obtained for the Sutterby nanofluid propulsion model reveal many engrossing behaviors and has many applications such as disease diagnostics and cancerous tissues destruction, and that provide a further dimension to investigate the nanofluid flow problems with thermophysical properties in two/three dimensions.

Movement of native fluids during scanning electron microscopy imaging of petroliferous siltstones: Evidence from the Montney Formation, western Canada

The nature and distribution of native fluids, both hydrocarbons and water, exert fundamental control on the petrophysical properties and fluid dynamics of unconventional, low-permeability reservoir rocks. Here, we report dynamic native fluid phenomena that occurred serendipitously during scanning electron microscopy (SEM) imaging of petroliferous siltstones from the Triassic Montney Formation of western Canada. These observations of fluid movement provide rare in-situ contextual information about the nm-to μm-scale distribution of fluids in tight unconventional reservoirs. Dynamic oil behaviour is indicated by expulsion structures that formed in pore-filling solid bitumen when trapped oil erupted from the sample while under vacuum pressure conditions. These structures strikingly show that oil and solid bitumen intimately coexist within the pore network of tight rocks in the oil reservoir-fluid window. Dynamic brine behaviour is evident from strings of halite crystals overlying pores between minerals. The halite crystals precipitated from hypersaline brine that migrated from the interior to the surface of the sample. This behaviour indicates well-connected brine exists in Montney siltstone pores, even those substantially filled with hydrophobic solid bitumen. These SEM observations support previous petrophysical studies that suggest the electrical conductivity of Montney rocks is controlled primarily by their bulk volume of well-connected hypersaline water.

Experimental study on elastic behaviors of two tandem risers in constant flow

Multiple pipes bundled with a certain distance are used for deep ocean development for such as lifting seafloor massive sulfides (SMS), pumping up a large amount of cooling water for onboard natural gas liquefaction, and production of oil/gas. To understand the vortex-induced phenomenon of fluids and the structural mutual interference among pipes in a steady flow, a towing tank test using a model of two vertical elastic pipes in tandem is performed. The parameters of this test are: the distance between the two pipes, the incident angle of crossflow with the inline direction of the pipes, the flow velocity (towing speed), and the boundary conditions of the tops of the pipes. The two horizontal accelerations of the towing direction and perpendicular direction are measured with synchronization. Then, the motion of the two pipes in each direction was measured, and the influence of the distance between the two pipes on the motion from the amplitude and phase information was analyzed. The results are investigated relatively in detail about the tandem arrangements of the two pipes to the incident flow. It is found that the major motion pattern of the two pipes in the tandem case is a rotational motion around the midpoint of two pipes.

HUSSERL AND DIMENSIONS OF TEMPORALITY: A FRAMEWORK FOR THE ANALYSIS OF TEMPORAL EXPERIENCE

Temporality is one of the key components of our experience, but the experience of time is hardly one and the same for all of us throughout our lives. The experience of time in its entirety is not solid and simple. It is a fluid and complex phenomenon consisting of a multitude of dimensions. In medical phenomenology and phenomenological psychopathology there are ample cases of different temporal experiences analysed in the context of the illness experience. However, only a few attempts have been made to propose a conceptual framework that could not only be used to conduct a concrete analysis in a more systematic manner, but also provide a solid and comprehensive theoretical basis. The aim of this article is to draw on the rich distinctions found in Husserl’s phenomenology to outline a framework of different temporal dimensions for the analysis of temporal experience. The framework could provide conceptual tools to analyse temporal experiences in any field of study that deals with the human experience, including medical phenomenology and phenomenological psychopathology. The resulting analysis would be not only clearer, more comprehensive and precise, but also more systematic and conceptually consistent. The framework consists of fourteen dimensions of temporal experience ordered in seven binary distinctions: (1) change and structure, (2) immanence and transcendence, (3) ownness and intersubjectivity, (4) passivity and activity, (5) receptivity and spontaneity, (6) presentation and representation, (7) unthematized temporality and thematized temporality.

Constriction length dependent instabilities in the microfluidic entry flow of polymer solutions.

Transport phenomena of fluids and particles through contraction and/or expansion geometries have relevance in many applications. Polymer solutions are often the transporter in these processes, giving rise to flow complexities. The separation distance between a contraction and a following expansion in microfluidic entry flow can affect the interplay between the shear and extension force dominated flow regimes, but the process is still little understood. We investigate the rheological responses of such constriction length dependent instabilities with three different polymer solutions and water in planar contraction-expansion microchannels differing only in the constriction length. The viscoelastic polyethylene oxide (PEO) solution is found to exhibit strong constriction length-dependent instabilities in both the contraction and expansion flows. Such a dependence is, however, completely absent from the flow of shear-thinning xanthan gum (XG) solution and Newtonian water. Interestingly, it is only present in the expansion flow of the both shear thinning and viscoelastic polyacrylamide (PAA) solution.