Chaotic Fluid Research Articles

Turbulent diffusion and air pollution: A comprehensive review of mechanisms, impacts, and modeling approaches

Turbulent diffusion is often a desirable phenomenon in many contexts, but it also presents significant challenges, particularly in the realm of air pollution. Air pollution, a universally recognized and frowned upon issue, degrades air quality and poses serious long-term health risks. Turbulent flows, characterized by chaotic and random fluid motions, give rise to turbulent diffusion, a process that acts as a transport mechanism for dispersing pollutants in the atmosphere. Despite its inherent complexities, the study of turbulent diffusion has advanced significantly, building on foundational concepts like Osborne Reynolds' decomposition in the 1850s and extending to Kolmogorov's length scale framework. These developments have enabled a deeper understanding of turbulent diffusion and its wide-ranging applications across various fields as new methods are continuously employed to broaden the scope of research and application.

Chaotic Behavior and Heat Transfer Analysis of Pulsating Flows with Different Frequencies

Due to the rapid development of electronic devices, the improvement of air–cooling methods for thermal management is urgent. In the present work, a promising way of coupling pulsating flow and vortex generators is proposed to eliminate the impacts of severe local high-temperature regions behind the vortex generators. Different from the traditional qualitative analysis, chaos is introduced to identify the quantitative impacts of the nonlinear dynamics of the coupling system. Particularly, the flow field was examined using the line stretching and the Poincaré map, and the chaotic characteristics of high-frequency pulsating flow were investigated. The results show that high-frequency pulsating flow enhances heat transfer mainly by promoting chaotic mixing. The chaotic fluid repeatedly stretches and folds, which increases the line stretching. Thus, the line stretching distribution can represent the heat transfer. Compared to the steady flow case, at Reynolds number of 1024 and pulsation frequency of 250 Hz, pulsating flow improves the Nusselt number by 5.82% and reduces friction factor by 2.62%, resulting in an improvement of thermal performance factor by 6.76%.

A fixed point analysis of fractional dynamics of heat transfer in chaotic fluid layers

This manuscript aims to analyze the chaotic fluid layer heating from below, using the Atangana–Baleanu derivative to characterize the existence and uniqueness of this chaotic model based on the provided fixed point data. First, with suitable examples, we demonstrate the existence and uniqueness of fixed point solutions within the framework of controlled metric spaces. Secondly, we study the chaotic behavior of water with various Rayleigh numbers by experimenting with it while keeping a constant Prandtl number. Furthermore, the role of the Rayleigh number in magnifying chaotic behaviors is examined, with graphical simulations demonstrating the effect of different fractional orders of the Atangana–Baleanu derivative. This research provides insights into the dynamics of chaotic systems and their practical applications in controlled situations.

Intermittency in the not-so-smooth elastic turbulence.

Elastic turbulence is the chaotic fluid motion resulting from elastic instabilities due to the addition of polymers in small concentrations at very small Reynolds ( ) numbers. Our direct numerical simulations show that elastic turbulence, though a low phenomenon, has more in common with classical, Newtonian turbulence than previously thought. In particular, we find power-law spectra for kinetic energy E(k) ~ k-4 and polymeric energy Ep(k) ~ k-3/2, independent of the Deborah (De) number. This is further supported by calculation of scale-by-scale energy budget which shows a balance between the viscous term and the polymeric term in the momentum equation. In real space, as expected, the velocity field is smooth, i.e., the velocity difference across a length scale r, δu ~ r but, crucially, with a non-trivial sub-leading contribution r3/2 which we extract by using the second difference of velocity. The structure functions of second difference of velocity up to order 6 show clear evidence of intermittency/multifractality. We provide additional evidence in support of this intermittent nature by calculating moments of rate of dissipation of kinetic energy averaged over a ball of radius r, εr, from which we compute the multifractal spectrum.

Auto‐Pressurized Multi‐Stage Tesla‐Valve Type Microreactors in Carbon Monoliths Obtained Through 3D Printing: Impact of Design on Fluid Dynamics and Catalytic Activity

AbstractThe present research exploits an innovative methodology for producing auto‐pressurized carbon microreactors with a precise and controlled structure analyzing the influence of their design on the fluid dynamics and their catalytic performance. Carbon monoliths with Tesla‐valve shape channels (Tesla, T, and modified Tesla, Tm) are synthesized through the combination of 3D printing and sol–gel process and further probed as Ni/CeO2 supports on CO2 methanation. The experimental results and mathematical modeling corroborated the improved performance obtained through the complex design compared to a conventional one. In addition to chaotic fluid flow induced by the deviation in flow direction, which improves the reagents‐active phase interaction, local pressure increases due to convergence of flows may enhance the Sabatier reaction according to Le Châtelier's principle. Conversely to straight channels, T and Tm are not affected by flow rate and presented chemical control. Tesla‐valve with curved angle (Tm) improved the mass transfer, achieving higher conversion and ≈30% reaction rate increase regarding right angle (T). Thus, this auto‐pressurized multi‐stage Tesla‐valve monolith opens the gate to design specific and advanced functional materials for multitude chemical reactions where not only the reactant‐active phase contact can be maximized but also the reaction conditions can be controlled to maximize the reaction kinetics.

A Spatial Correlation Identification Model for Coherent Structure Extraction and Three-Dimensional Visualization

Multi-scale coherent structures have been observed in ocean currents, which are induced by the interaction of shear flows with different velocities. Understanding the spatial configuration and scale characteristics of coherent structures will promote the explanation of physical ocean phenomena. Considering the self-similarity, we propose a spatial correlation identification model for coherent structure extraction and three-dimensional visualization based on the wavelet transform and time-dependent intrinsic correlation method. The spatial and scale distributions of coherent structures are related to the dissipation rate variation. Most large-scale coherent structures, with the largest length scale of 13 m, are found to exist in stable fluid, such as the water column below 50 m. However, small-scale structures are found in chaotic fluids, such as the upper layer. Furthermore, we found that coherent structures of different scales coexist simultaneously in the same depth range, indicating a simultaneous multi-scale structure pattern for turbulent flow investigations.

β-Variational autoencoders and transformers for reduced-order modelling of fluid flows

Variational autoencoder architectures have the potential to develop reduced-order models for chaotic fluid flows. We propose a method for learning compact and near-orthogonal reduced-order models using a combination of a β-variational autoencoder and a transformer, tested on numerical data from a two-dimensional viscous flow in both periodic and chaotic regimes. The β-variational autoencoder is trained to learn a compact latent representation of the flow velocity, and the transformer is trained to predict the temporal dynamics in latent-space. Using the β-variational autoencoder to learn disentangled representations in latent-space, we obtain a more interpretable flow model with features that resemble those observed in the proper orthogonal decomposition, but with a more efficient representation. Using Poincaré maps, the results show that our method can capture the underlying dynamics of the flow outperforming other prediction models. The proposed method has potential applications in other fields such as weather forecasting, structural dynamics or biomedical engineering.

Low-spatial-coherence random lasers enhanced by TiN/Graphene self-assembly structures for high-resolution imaging in chaotic fluid environments

Low-spatial-coherence random lasers enhanced by TiN/Graphene self-assembly structures for high-resolution imaging in chaotic fluid environments

CFD of Fully Developed Channel Flow

Turbulent flow, characterized by random and chaotic fluid motion, is a common occurrence in many engineering applications, such as aerospace, wind turbines, hydroelectric power plants, and chemical mixing processes. In these applications and others, the turbulent flows often involve complex geometries, multiple scales of motion, and nonlinear interactions, which make it challenging to simulate and predict turbulent flow behaviour accurately. As a result, turbulence modelling plays a crucial role in these applications by providing an efficient and cost-effective way to model the complex physics of turbulent flows. Several turbulence models have been developed and are commonly used in computational fluid dynamics (CFD) simulations to predict the behaviour of turbulent flows. In this work, the Navier-Stokes equations and transport equations of turbulent kinetic energy and turbulent dissipation are solved using finite difference approximation. In-house MATLAB code is developed in this work to solve the two-dimensional, incompressible, fully developed turbulent channel flow for Reynolds number ranged from 6000 to 12000.

Two-dimensional long-range uniaxial order in three-dimensional active fluids

Elongated active units cannot spontaneously break rotation symmetry in bulk fluids to form nematic or polar phases. This has led to the image of active suspensions as spontaneously evolving, spatiotemporally chaotic fluids. Here, in contrast, I show that bulk active fluids have stable active nematic and polar states at fluid–fluid or fluid–air interfaces. The active flow-mediated long-range interactions that destroy the ordered phase in bulk lead to long-range order at the interface. Thus, active fluids have a surface ordering transition and form states with quiescent, ordered surfaces and chaotic bulk. I further consider active units that are constrained to live at an interface to examine the minimal conditions for the existence of two-dimensional order in bulk three-dimensional fluids. In this case, immotile units do not order, but motile particles still form a long-range-ordered polar phase. This prediction of stable, uniaxial, active phases in bulk fluids may have functional consequences for active transport. Bulk active fluids are unstable because activity destroys long-range ordering. Now, a model of 3D active liquids shows that stable states can form at fluid–fluid surfaces.

Machine learning prediction and multiobjective optimization for cooling enhancement of a plate battery using the chaotic water-microencapsulated PCM fluid flows

BackgroundThe cooling of electric vehicle batteries is a crucial issue to increase the performance of the next-generation cars and develop market acceptance. There are various ideas for heat transfer enhancement of the batteries of an electric vehicle. However, it still requires more attention and research to raise the thermal management systems for the batteries. MethodsThe current study seeks the effects of simultaneous use of the chaotic flow and microencapsulate phase change materials for cooling a plate battery. Three values for Reynolds numbers from 100 to 300 and volume fractions from 0 to 10% in various geometries are evaluated. The results are presented through the variations of thermo-hydrodynamic parameters. A multiobjective optimizer combined with an artificial neural network finds optimum working conditions aiding some decision makers. Significant findingsThe Nusselt number of the suspension in the proposed geometries can increase up to 23% compared to that for the pure water in the straight channel. However, it may follow the friction factor strengthening by 160%. It is shown that the proposed geometries are mostly affected by the latter parameter. The efficiency of the proposed geometry accelerates from that of the conventional channel by increasing the Reynolds number and volume fraction.

A Novel Approach for Flow Analysis in Pulsating Heat Pipes: Cross-Correlation of Local Heat Flux

Pulsating heat pipe is a promising two-phase heat transfer device that has many advantages such as a simple wickless structure and high thermal performance. Its thermal behavior is inherently time-dependent, and it can also be characterized by substantial spatial variations. However, there are few studies investigating the interaction or similarity of the local physical quantities, such as heat fluxes exchanged between the working fluid and the device wall in adjacent branches. In the present work, a new approach based on the application of cross-correlation analysis to local heat fluxes is proposed to deepen the understanding of the flow characteristics in pulsating heat pipes. The temperature distribution in the condenser of a seven-turn pulsating heat pipe was measured with an infrared camera, changing the power input. The local heat flux distributions were estimated by solving the inverse heat conduction problem in the tube wall. The cross-correlation of the heat fluxes at different positions of central and edge tubes in the condenser was analyzed. The result revealed the different trends in the cross-correlation depending on the power input: there were no clear cross-correlations in 0.5 W, while it was shown more clearly on the diagonal line with increasing power input to 2 W and 3.5 W because of the more activated flow throughout the heat pipe than that of the low power input. Moreover, the results of 3.5 W indicated a synchronized flow. It is suggested that the original approach presented in this work would lead to a deeper understanding of the chaotic fluid oscillation in pulsating heat pipes.

Local investigation of the dynamic and thermal fields to characterize the transition onset from steady to unsteady laminar flow in a complex geometry

The present work investigated numerically the onset of the transition from steady to unsteady laminar flow regime in a three dimensional complex geometry. The behavior of the dynamic and thermal fields of the chaotic fluid flow has been analyzed for numerous Reynolds numbers ranging from 190 to 550. Several parameters were used during this study to verify the fluid pattern such as; velocity and temperature profiles, secondary flow, flow intensity, helicity and the Nusselt number. It is found that at Re = 400, the symmetry of the flow is destroyed in the second and the third geometric periods whereas it still remains present in the first period which indicates the first step towards the transition. While at Re = 445, the symmetry is still preserved in the first period of the geometry, but the velocity begins to be unsteady with periodic variation at a single frequency where a clear impression can be given on the transition from the steady laminar regime to the unsteady regime. Results illustrate that the flow goes through intermediate steps to reach the unsteady domain before exiting the laminar zone. Moreover, the flow in the geometry of interest is not of the same nature so it can be totally or partially unsteady where different stages can be cited as; stable and symmetric flow, stable asymmetric flow, unstable flow with one or more frequencies and finally erratic flow.

Wire-wrapped and helically-finned tubular ceramic membranes for enhancing water and waste heat recovery from wet flue gas

Recycling water and waste heat from wet flue gas is crucial for sustainable energy-water-environment nexus in industrial processes. Herein, we report the use of wire-wrapped and helically-finned tubular ceramic membranes to construct membrane condensers for simultaneous water and heat recovery. Compared with conventional plain tubular ceramic membrane (PTCM), wire-wrapped tubular ceramic membrane (WTCM) and helically-finned tubular ceramic membrane (FTCM) both exhibit superior water and heat recovery performance, indicating a non-negligible effect of chaotic fluid mixing on heat and mass transfer enhancement. FTCM shows better condensate capture performance than WTCM. Moreover, improved condensing heat transfer performances are observed on FTCMs provided with large fin height and pitch. FTCM provides higher heat transfer coefficients than PTCM at around 7.4% to 59.3% depending on different fin structures. Effects of operation parameters on membrane condensation process using FTCM are also investigated. Gas-side parameters have significant effects on water/heat recovery performance than water-side parameters. This study can serve as a basis for process intensification of membrane-based condensation used for flue gas dehumidification.

Direct Correlation between Fluid Cluster Structure and Its Viscosity

The research purpose is to prove the probability of a direct quantitative correlation between proportion of these clusters and liquid viscosity. A quasi-polycrystalline clustering model of the liquid (in particular, melts) should be used. The Boltzmann distribution, the concepts of the chaotic particles and the virtual cluster size distribution should be applied to achieve this purpose. This study analyzed the complete reference data on the temperature dependences of the dynamic viscosity for the alkali metals. As a result, a directly proportional correlation between viscosity and cluster content in liquid has been determined. It has provided the probabil-ity for the quantitative concept of the quasi-polycrystalline clustering model on the liquid state of matter due to its properties. The concept of the chaotic particles in direct correlation to the Boltzmann distribution has been used as a basis. The Boltzmann energy spectrum has been used for the kinetic energy of the chaotic thermal particle motion in the solid, liquid and gaseous states of matter. As a result, their three energy classes have been distinguished with their presence in all aggregate states and in the sum constantly equal to one. Formulas to calculate the proportion of the virtually ordered clustering and complete chaotic fluid compo-nents were deduced. These formulas have been derived with using the particle distributions by the energy class and cluster sizes.

Dynamical system analysis of a data-driven model constructed by reservoir computing.

This study evaluates data-driven models from a dynamical system perspective, such as unstable fixed points, periodic orbits, chaotic saddle, Lyapunov exponents, manifold structures, and statistical values. We find that these dynamical characteristics can be reconstructed much more precisely by a data-driven model than by computing directly from training data. With this idea, we predict the laminar lasting time distribution of a particular macroscopic variable of chaotic fluid flow, which cannot be calculated from a direct numerical simulation of the Navier-Stokes equation because of its high computational cost.

ЦИТОПРОТЕКТОРНА ТЕРАПІЯ ПАЦІЄНТІВ З РЕСПІРАТОРНОЮ ПАТОЛОГІЄЮ: ВЛАСТИВОСТІ ЕКТОЇНУ

CYTOPROTECTIVE THERAPY FOR PATIENTS WITH RESPIRATORY PATHOLOGY: PROPERTIES OF EKTOIN S. V. Zaikov, A. E. Bogomolov, L. V. Mikhei Abstract In light of the often irrational use of antibiotics, the growing problem of antibiotic resistance of respiratory pathogens and certain imperfections in the management of patients with acute and chronic rhinosinusitis, acute and chronic bronchitis, exacerbations of chronic obstructive pulmonary disease, there is always a need to seek for a new (non-antibacterial) methods of treatment to increase the effectiveness of therapy in these categories of patients. Probably, cytoprotection may also become one of these methods. Aim — to analyze the results of ectoine use as a respiratory cytoprotector. Material and methods. Analysis of available scientific publications on the use of ectoine in medical practice has been done. Conclusions. Ectoin is a natural molecule of extremolyte that strengthens the bonds and the number of neighboring water molecules, organizes water from a chaotic fluid into a structured Ectoin® Hydro Complex, which surrounds mucous cells with a protective layer of water and leads to barrier protection of the mucous membrane. The natural molecule of ectoine has anti-inflammatory, membrane-stabilizing and cytoprotective properties. Ectoin is used for barrier protection and recovery of the mucous membrane of the respiratory tract in acute and chronic diseases of the upper and lower respiratory tract. Efficacy and safety of ectoine, including its long-term use, werev proved by the results of preclinical and clinical studies. Key words: cytoprotective therapy, ectoine, respiratory pathology

Experimental Observations of Lagrangian Coherent Structures and Fluid Transports in Perturbed Rayleigh-Bénard Convection

Abstract In this paper, we make experimental observations of the perturbed Rayleigh-Benard convection to detect the Lagrangian coherent structures (LCSs), which correspond to the invariant manifolds of time-dependent systems and also to investigate the associated fluid transports by numerically integrating the two-dimensional velocity field obtained by Particle Image Velocimetry (PIV). We show the chaotic fluid transports that appear in the system, though some particles are transported almost periodically with time period T or 3T, where T = 17.3 s is the period of the perturbation. We finally propose a novel perturbed Hamiltonian system that enables to recover qualitatively global behaviors observed in experimental results and we also explore the periodic fluid transport that appear in the system.

Experimental Observations of Perturbed Rayleigh-Benard Convection and Analysis of Chaotic Fluid Transport

Experimental Observations of Perturbed Rayleigh-Benard Convection and Analysis of Chaotic Fluid Transport

Steady Euler flows and Beltrami fields in high dimensions

AbstractUsing open books, we prove the existence of a non-vanishing steady solution to the Euler equations for some metric in every homotopy class of non-vanishing vector fields of any odd-dimensional manifold. As a corollary, any such field can be realized in an invariant submanifold of a contact Reeb field on a sphere of high dimension. The solutions constructed are geodesible and hence of Beltrami type, and can be modified to obtain chaotic fluids. We characterize Beltrami fields in odd dimensions and show that there always exist volume-preserving Beltrami fields which are neither geodesible nor Euler flows for any metric. This contrasts with the three-dimensional case, where every volume-preserving Beltrami field is a steady Euler flow for some metric. Finally, we construct a non-vanishing Beltrami field (which is not necessarily volume-preserving) without periodic orbits in every manifold of odd dimension greater than three.