Fluid Phenomena Research Articles

Critical phenomena in compressible polar active fluids: Dynamical and functional renormalization group studies

Active matter is not only relevant to living matter and diverse nonequilibrium systems, but also constitutes a fertile ground for novel physics. Indeed, dynamic renormalization group (DRG) analyses have uncovered many new universality classes (UCs) in polar active fluids (PAFs)---an archetype of active matter systems. However, due to the inherent technical difficulties in the DRG methodology, almost all previous studies have been restricted to polar active fluids in the incompressible or infinitely compressible (i.e., Malthusian) limits, and, when the $\ensuremath{\epsilon}$ expansion was used in conjunction, to the one-loop level. Here, we use functional renormalization group (FRG) methods to overcome some of these difficulties and unveil critical behavior in compressible polar active fluids, and calculate the corresponding critical exponents beyond the one-loop level. Specifically, we investigate the multicritical point of compressible PAFs, where the critical order-disorder transition coincides with critical phase separation. We first study the critical phenomenon using a DRG analysis and find that it is insufficient since two-loop effects are important to obtain a nontrivial correction to the scaling exponents. We then remedy this defect by using a FRG analysis. We find three universality classes and obtain their critical exponents, which we then use to show that at least two of these universality classes are out of equilibrium because they violate the fluctuation-dissipation relation.

Computing Lagrangian means

Lagrangian averaging plays an important role in the analysis of wave–mean-flow interactions and other multiscale fluid phenomena. The numerical computation of Lagrangian means, e.g. from simulation data, is, however, challenging. Typical implementations require tracking a large number of particles to construct Lagrangian time series, which are then averaged using a low-pass filter. This has drawbacks that include large memory demands, particle clustering and complications of parallelisation. We develop a novel approach in which the Lagrangian means of various fields (including particle positions) are computed by solving partial differential equations (PDEs) that are integrated over successive averaging time intervals. We propose two strategies, distinguished by their spatial independent variables. The first, which generalises the algorithm of Kafiabad (J. Fluid Mech., vol. 940, 2022, A2), uses end-of-interval particle positions; the second uses directly the Lagrangian mean positions. The PDEs can be discretised in a variety of ways, e.g. using the same discretisation as that employed for the governing dynamical equations, and solved on-the-fly to minimise the memory footprint. We illustrate the new approach with a pseudo-spectral implementation for the rotating shallow-water model. Two applications to flows that combine vortical turbulence and Poincaré waves demonstrate the superiority of Lagrangian averaging over Eulerian averaging for wave–vortex separation.

Modelling and analysis of hydrodynamics and flow phenomena of fluid with formic acid as pollutant in the reactive area of a flat plate photocatalytic reactor with top and bottom turbulence promote

The inadequate mixing of pollutant and its low mass transfer in the reactive surface reduces the efficiency of photocatalytic reactor. A computational model is developed, and numerical analysis is conducted to examine the effect of top and bottom baffles on the mass transfer and hydrodynamic performance of the reactor compared to reactor without baffle in this study. The hydrodynamic flow phenomena such as local streamlines, velocity, turbulence characteristic, pressure-drops, and wall shear stress were investigated. The experiment was done in a lab-scale flat-plate photocatalytic reactor using Formic Acid as pollutant in feed water for model validation. The FA concentration versus feed flow rate and velocity as a function of time showed good agreement between simulation and experimental results (only about 5 % variation). From the simulation, it was found that the pressure drops increase with increase in baffle height and the lowest was found to be 0.1 kPa and 0.4 kPa when the baffle height was 5 mm at velocity of 0.15 m/s and 0.5 m/s respectively. The highest turbulent kinetic energy and the dissipation was found 0.215 m2/s2 and 46 m2/s3 respectively when the baffle height was 12 mm in the present simulation. Baffles significantly changes the hydrodynamic performance such as turbulence, velocity, mass of pollutant and the pressure drops. The velocity magnitude also increases and the highest was found to be 9.2 times of the free stream velocity when 12 mm top baffle was used. Similar trends were found for bottom baffles. The highest magnitude of turbulent kinetic energy was found to be four times higher than the plain reactor without baffle. Therefore, baffle will significantly promote turbulence and improve the hydrodynamic performance thus enhance the photocatalytic rector performance.

Analogy between Turbulent-to-Vortex Shedding Flow Transition in Fluids and Ductile-to-Brittle Failure Transition in Solids

By using complex potentials, some light is shed on the analogy between the singularity problems arising in fluid and fracture mechanics—in particular, those concerning plane irrotational flows around sharp obstacles and plane elasticity in cracked bodies. Applications to two equivalent geometries are shown: a thin plate transversally immersed in a uniform flow and a crack subjected to uniform out-of-plane shearing stress at infinity (Mode III). The matching between the fluid velocity field and the shearing stress field is consistent with the hydrodynamic analogy. Aside from the Reynolds criterion for the natural laminar-to-turbulent transition, a velocity-intensity factor criterion is defined to predict the forced turbulent-to-vortex-shedding fluid-flow transition (forced transitional flow) generated by a transversal plate obstacle. It is interesting to remark that the velocity-intensity factor presents physical dimensions intermediate between those of a velocity and a kinematic viscosity. In addition, it will be demonstrated that size affects the occurrence of natural-to-forced transitional phenomena in fluids, in a strict analogy to the scale-dependent ductile-to-brittle failure transitions in solids.

3D Numerical Analysis of a Phase Change Material Solidification Process Applied to a Latent Thermal Energy Storage System

The techniques for releasing thermal energy accumulated in periods of high availability to meet the demand in periods of low energy supply contribute to the continuity of the cycles involved in thermodynamic processes. In this context, phase change materials are capable of absorbing and releasing large amounts of energy in relatively short periods of time and under specific operating conditions. However, phase change materials have low thermal conductivity and need to be coupled with high-thermal-conductivity materials so that the heat flux can be intensified and the energy absorption and release times can be controlled. This work aims to numerically study the solidification process of a phase change material inserted into a triplex tube heat exchanger with finned copper walls to intensify the thermal exchange between the phase change material and the cooling heat transfer fluid, water, that will receive the energy accumulated in the material. This work proposes the 3D numerical modeling of the triplex tube heat exchanger with finned walls and meets the need for numerical models that allow for the analysis of the full geometry of the latent heat thermal energy storage system and the thermal and fluid dynamic phenomena that are influenced by this geometry. Results of the temperature, liquid fractions and velocity fields during phase transformations are presented, analyzed and validated with experimental data, presenting average errors of below 5%. The total material discharge time was approximately 168 min, necessary for the complete solidification of the phase change material, with water injected into the triplex tube heat exchanger at a flow rate of 8.3 L/min and a temperature of 68 °C. The solidification process occurred more slowly in the same direction as the length of the triplex tube heat exchanger, and from 80% of the material in the solid state, the difference between the solidification time for z = 0 and z = 480 mm was 30 min. The fluid dynamic conditions developed in the latent heat thermal energy storage system promoted a maximum negative heat flux of −6423 w/m2 to the annular internal surface and −742 w/m2 to the annular external surface, representing a heat removal process nine times less intense on the external surface. The total energy released to the cooling heat transfer fluid was 239.56 kJ/kg.

Thermo-Resistive Phase Behavior of Trivalent Ion-Induced Microscopic Protein-Rich Phases: Correlating with Ion-Specific Protein Hydration

Proteins, in the presence of trivalent cations, exhibit intriguing phase behavior which is contrasting compared to mono- and divalent cations. At room temperature (RT), trivalent cations induce microscopic liquid-liquid phase separation (LLPS) in which a protein-rich phase coexists with a dilute phase. The critical solution temperature related phenomena in these complex fluids are well studied; however, such studies have mostly been restricted below the denaturation temperature (TM) of the protein(s) involved. Here, we probe the phase behavior of bovine serum albumin (BSA) incubated at 70 °C (>TM) in the presence of Na+, Mg2+, La3+, Y3+, and Ho3+ ions. BSA in the presence of mono- and bivalent ions forms an intense gel phase at 70 °C; however, the trivalent salts offer remarkable thermal resistivity and retain the fluid LLPS phase. We determine the microscopic phase behavior using differential interference contrast optical microscopy, which shows that the LLPS droplet structures in the M3+ ion-containing protein solutions prevail upon heating, whereas Mg2+ forms composed cross-linking gelation upon thermal incubation. We probe the interior environment of the protein aggregates by ps-resolved fluorescence anisotropy measurements using 8-anilino-1-naphthalenesulfonic acid (ANS) as an extrinsic fluorophore. It reveals that while the LLPS phase retains the rotational time constants upon heating, in the case of gelation, the immediate environment of ANS gets significantly perturbed. We investigate the explicit protein hydration at RT as well as at T > TM using the ATR THz-FTIR (1.5-22.5 THz) spectroscopy technique and found that hydration shows strong ion specificity and correlates the phase transition behavior.

Quantifying the hybrid flow and aperture forming of liquid metals immersed in NaOH solution under rotating magnetic field

AbstractLiquid metal (LM) immersed in solutions exhibited profound fluidic phenomena under various working situations. With persistent research endeavor, a growing number of intriguing phenomena along this direction have been increasingly disclosed. Among the many critical issues, quantifying the hybrid flow of LMs and surrounding solutions often encounters tough challenges due to the large property differences between the two fluids, including density, electrical and fluidic characteristics, and so forth. Especially, when the electromagnetic field is involved, the problems would become ever complicated. In this article, to characterize the hybrid fluids of LM and NaOH solution under rotating magnetic field (RMF), we established a coupled three‐dimensional model considering magnetic effect on the two‐phase flow. The computational prediction of the model was validated through comparing the simulated morphological features of LM with the experimental measurements at different rotational speeds of magnetic field. Finally, two phenomena were revealed with potential applications interpreted: (1) LM would accelerate the solution due to their difference in viscosity; (2) an asymmetric flow and tunable hole formation under RMF will occur due to the surface tension redistribution on LM. The present works are expected to provide reliable guidance for quantifying the multiphase flow behaviors of hybrid fluids composed of LM and other liquids. The revealed hole size dominated LM aperture is especially useful for developing future smart optical switch and electromagnetic shielding devices.

Benefits and Barriers of Digital Procurement: Lessons from an Airport Company

Implementing a well-integrated procurement system and applying uniform practices to achieve the strategic goals of any company is a complex phenomenon. Navigating the digital procurement systems in achieving supply-chain resilience remains a predicament. Framed within the technology acceptance model (TAM), which is a key model in understanding the predictors of human behaviour toward the potential acceptance or rejection of the technology. This study explored the benefits and barriers of digital procurement at Airports Company South Africa (ACSA). A qualitative approach in a form of a single holistic case study design was adopted. The sample involved 18 employees and individuals who were supply chain management (SCM), information technology (IT), and programme management office (PMO) professionals. Semi-structured interviews conducted focused on those with extensive experience on procurement, digital technologies, procurement automation or the implementation of transformation programmes. Digital procurement is a value-adding function at ACSA with the possibilities of providing cost reduction in the supply chain. However, the participants highlighted job losses, cyber security, lack of interoperability, lack of skills and system downtimes as obstacles affecting the adoption of digital procurement and as organizational barriers. The infusion of digital technologies into various aspects of organisational processes and outcomes remains a complex, dynamic, fluid, and volatile phenomenon. A framework highlighting critical focus areas when it comes to the adoption of digital procurement of digitalization is presented.

Obtaining soliton solutions of the nonlinear (4+1)-dimensional Boiti–Leon–Manna–Pempinelli equation via two analytical techniques

This paper tackles the recently introduced (4+1)-dimensional Boiti–Leon–Manna–Pempinelli equation (4D-BLMPE) utilized to model wave phenomena in incompressible fluid and fluid mechanics. Modified extended tanh expansion method (METEM) and the new Kudryashov scheme are implemented to produce analytical soliton solutions for the presented equation. The traveling wave transformation is constructed, and the homogeneous balance principle is utilized to apply the two proposed techniques. Furthermore, the flat-kink, smooth-kink, singular, and periodic singular solutions are successfully extracted. Some produced solutions are illustrated graphically to understand the physical meaning of the presented model. Moreover, for the first time in this study, the effect of model parameters on kink soliton dynamics is examined, and graphical representations are depicted and interpreted.

The periodic secondary flow of Oldroyd-B fluids driven by direct electric field in a rectangular curved channel

The electro-osmotic flow of Oldroyd-B fluids in a 90° curved tube with a rectangular section under a direct electric field is numerically studied. By introducing elastic forces into the force balance of viscous, electric, and centrifugal forces, another secondary flow pattern is found in addition to the stable state for Newtonian fluids, i.e., the periodic oscillation state. In this oscillating state, the position of the maximum velocity periodically moves from the center to the position near the wall. Meanwhile, a symmetric vortex can be periodically observed in the streamline figures. The secondary flow oscillates when the Deborah number De or the dimensionless wall potential ψ is sufficiently large, and the oscillating frequency increases with a larger Deborah number De or a larger dimensionless wall potential ψ. A phase diagram of the secondary flow as it depends on the Deborah number De and the dimensionless wall potential ψ is presented. There is a critical Deborah number Decr for a given wall potential ψ, and the secondary flow become periodically oscillating at De>Decr. The critical Deborah number Decr decreases as the value of the dimensionless wall potential ψ increases. Moreover, the critical Deborah number should be larger than 0.2 even though the wall potential ψ further increases, i.e., Decr>0.2. At De≤0.2, the elastic forces are small, and the secondary flow is stable rather than oscillating similar to the phenomena of Newtonian fluids.

Porous Structural Microfluidic Device for Biomedical Diagnosis: A Review.

Microfluidics has recently received more and more attention in applications such as biomedical, chemical and medicine. With the development of microelectronics technology as well as material science in recent years, microfluidic devices have made great progress. Porous structures as a discontinuous medium in which the special flow phenomena of fluids lead to their potential and special applications in microfluidics offer a unique way to develop completely new microfluidic chips. In this article, we firstly introduce the fabrication methods for porous structures of different materials. Then, the physical effects of microfluid flow in porous media and their related physical models are discussed. Finally, the state-of-the-art porous microfluidic chips and their applications in biomedicine are summarized, and we present the current problems and future directions in this field.

A thermodynamics-informed active learning approach to perception and reasoning about fluids

Learning and reasoning about physical phenomena is still a challenge in robotics development, and computational sciences play a capital role in the search for accurate methods able to provide explanations for past events and rigorous forecasts of future situations. We propose a thermodynamics-informed active learning strategy for fluid perception and reasoning from observations. As a model problem, we take the sloshing phenomena of different fluids contained in a glass. Starting from full-field and high-resolution synthetic data for a particular fluid, we develop a method for the tracking (perception) and simulation (reasoning) of any previously unseen liquid whose free surface is observed with a commodity camera. This approach demonstrates the importance of physics and knowledge not only in data-driven (gray-box) modeling but also in real-physics adaptation in low-data regimes and partial observations of the dynamics. The presented method is extensible to other domains such as the development of cognitive digital twins able to learn from observation of phenomena for which they have not been trained explicitly.

Numerical Computation of Hybrid Morphologies of Nanoparticles on the Dynamic of Nanofluid: The Case of Blood-Based Fluid

The movement of biological fluids in the human body is a premium field of interest to overcome growing biomedical challenges. Blood behavior shows different behavior in capillaries, veins, and arteries during circulation. In this paper, a new mathematical relation for the nano-layer of biological fluids flows with the effect of TiO2 and Ag hybrid nanoparticles was developed. Further, we explain the engineering phenomena of biological fluids and the role of hybrid nanoparticles in the blood vessel system. The improvement of drug delivery systems by using low seepage Reynolds number was associated with expansion/contraction and was discussed in detail through the rectangular domain. Using similarity transformation, the governing equations were converted into non-linear ordinary differential equations, and the mathematical problem was solved by employing the numerical shooting method. Plots of momentum, temperature, skin friction coefficient, as well as the Nusselt number on different non-dimensionless parameters are displayed via lower/upper porous walls of the channel. It was analyzed that the walls of the channel showed different results on magnetized physical parameters. Values of thermophoresis and the Brownian motion flow of the heat transfer rate gradually increased on the upper wall and decreased on the lower wall of the channel. The important thing is that the hybrid nanoparticles, rather than nano, were more useful for improving thermal conductivity, heat transfer rate, and the nano-layer.

An artificial neural network approach to bifurcating phenomena in computational fluid dynamics

This work deals with the investigation of bifurcating fluid phenomena using a reduced order modelling setting aided by artificial neural networks. We discuss the POD-NN approach dealing with non-smooth solutions set of nonlinear parametrized PDEs. Thus, we study the Navier–Stokes equations describing: (i) the Coanda effect in a channel, and (ii) the lid driven triangular cavity flow, in a physical/geometrical multi-parametrized setting, considering the effects of the domain’s configuration on the position of the bifurcation points. Finally, we propose a reduced manifold-based bifurcation diagram for a non-intrusive recovery of the critical points evolution. Exploiting such detection tool, we are able to efficiently obtain information about the pattern flow behaviour, from symmetry breaking profiles to attaching/spreading vortices, even in the advection-dominated regime.

Rheological insight of wall slippage and microrotation on the coating thickness during non-isothermal forward roll coating phenomena of micropolar fluid

Rheological insight of wall slippage and microrotation on the coating thickness during non-isothermal forward roll coating phenomena of micropolar fluid

Technological socialities: The impact of information and communication technologies on belonging among deaf and hard‐of‐hearing people

AbstractThis review article examines how different types of communication technologies, from the specialized medical to generic social devices, influence belonging and sociality among deaf and hard‐of‐hearing (DHH) people. The emphasis is on DHH adolescents and young adults who may be impacted differently across countries, given state‐specific policies regarding the status of sign language and deaf education, and based on different availability, affordability, and accessibility of communication technologies. We introduce different perspectives on deafness, ranging from pathological to cultural, a heuristic on which we build to explore DHH socialities as complex and evolving. We then analytically review ethnographic research on how cochlear implants impact DHH people's belonging to the “deaf world” and/or the “hearing world,” and how they navigate between these worlds. Then we move on to technologies such as text messages and social media, which enable DHH people to extend their socialities beyond local communities. Belonging is a fluid phenomenon, and technologies which are in a constant process of innovation and development may influence it in complex ways. We argue that to explore questions of belonging, identity, and sociality among DHH people, and how they are shaped by technologies, (visual) ethnographic methods are particularly productive.

The “Thermocapillary-based control of a free surface in microgravity” experiment

Present and future challenges of space exploration require better and improved strategies for fluid control and management. The “Thermocapillary-based control of a free surface in microgravity” (ThermoSlosh) experiment aims to contribute directly to current knowledge and basic understanding of fluid phenomena in reduced gravity, in particular, to study the effectiveness of thermal forcing for fluid control in weightlessness and applications. The experiment proposes to analyze the dynamics of a free surface in a cylindrical cell, half filled with 5 cSt silicone oil, subjected to controlled temperatures and accelerations. Simulations suggest that the thermocapillary effect can be used in microgravity to control the orientation of the free surface within the cell. The response of the free surface to the applied thermal gradient is characterized using the rise time, the stabilization time, and the overshoot; these representative quantities further help evaluating the effectiveness of the strategy. The use of supplemental vibrations is shown to improve the overall performance of the thermal control. Finally, among various potential applications, the ability to control sloshing motion during the real microgravity scenario of an ISS reboosting maneuver is assessed. ThermoSlosh was recently presented to the International Space Science and Scientific Payload competition, and is part of the selected proposals for the competition final.

Pulse and pulsating supercharging phenomena in a semi-enclosed pipe

Considering the discontinuous square pulse wave and continuous sine pulsating wave, we report a distinctive supercharging phenomenon of fluid in a water-filled semi-enclosed pipe and reveal the supercharging regularity. We demonstrate that there can be significant supercharging phenomena at the pipe end-face if the water is periodically injected at the pipe inlet with certain frequency. Compared to the traditional pulsating injection method, the present injection strategy can remarkably enhance the peak pressure of the water at the end face of the pipe. We explained this phenomenon by numerical simulations based on the computational fluid dynamic method. It’s found that there is a quantitative relationship between the optimal pulse frequency, pipe length and wave speed. The proposed frequency model is suitable for the multi-waveform, such as sine wave, square wave and arcuate wave. The fluid pressure at the pipe end-face intermittently increases and the end-face peak pressure is largest when the inlet injection frequency equals to the optimal frequency.

Alignment rule and geometric confinement lead to stability of a vortex in active flow.

Vortices are hallmarks of a wide range of nonequilibrium phenomena in fluids at multiple length scales. In this work, we numerically study the whirling motion of self-propelled soft point particles confined in circular domain, and aim at addressing the stability issue of the coherent vortex structure. By the combination of dynamical and statistical analysis at the individual particle level, we reveal the persistence of the whirling motion resulting from the subtle competition of activity and geometric confinement. In the stable whirling motion, the scenario of the coexistence of the irregular microscopic motions of individual particles and the regular global whirling motion is fundamentally different from the motion of a vortex in passive fluid. Possible orientational order coexisting with the whirling are further explored. This work shows the stability mechanism of vortical dynamics in active media under the alignment rule in confined space and may have implications in creating and harnessing macroscale coherent dynamical states by tuning the confining geometry.

FLUID LEAVES: EFFECTS OF FLUID FLOW ON LEAF SHAPES AND FIBONACCI SERIES

The liquid chain and other fluid phenomena, which resemble leaves of plants, are categorized as fluid leaves. Liquid chain happens when two liquid jets hit each other at an angle, or when the liquid jet flows on smooth surfaces. Liquid leaves are not just limited to fluid engineering, but also to biology. The literature shows that the liquid chain looks like leaves, but there are not many resources explaining the physics of the shape being in the form of a leaf. In this work, the author shows that liquid impacting different types of surfaces does form a leaf–like structure. The detailed theory on biology and liquid leaves is mentioned in the application section for better understanding of the scope of this study. This paper visualizes different types of leaves with changes in surface types, and it also reports a new property of fluids found from a simple experiment involving the droplet coalescence. It is remarkable to find that the fluid property is the reason for Fibonacci Series in the universe, including living and non-living things.