3D Fluid Research Articles

Enabling multi-resolution droplet-on-demand metal jetting through tailored pulsing

Like most additive manufacturing methods, droplet-based molten metal jetting (MMJ) techniques face a fundamental trade-off between printing resolution and speed, which naturally imposes limits on the fabrication of parts. Herein, we present some of these limits and propose a novel method and nozzle design to circumvent them: multi-resolution metal additive manufacturing via magnetohydrodynamic (MHD) droplet-on-demand MMJ. Multi-resolution printing enables high resolution and high deposition by selectively ejecting molten metal droplets of varying size from a single-reservoir nozzle equipped with two orifices. When ejecting droplets from the smaller orifice, fine resolution features can be printed at the expense of deposition rate. Conversely, larger orifices allow coarser features to be printed quickly. The complexity of activating only a single orifice is overcome by carefully tailoring MHD pulses to comply with the characteristic fluid dynamics of each individual orifice. The concept is established using 3D fluid dynamics simulations of a nozzle equipped with two orifices (200 and 500 μm diameter) and validated experimentally with an identical nozzle configuration using an aluminum alloy as the ejection liquid.

1D fluids with repulsive nearest-neighbour interactions: low-temperature anomalies

Abstract A limited number of two-dimensional and three-dimensional materials under a constant pressure contract in volume upon heating isobarically; this anomalous phenomenon is known as the negative thermal expansion (NTE). In this paper, the NTE anomaly is observed in 1D fluids of classical particles interacting pairwisely with two competing length scales: the hard-core diameter a and the finite range a ′ > a of a soft repulsive potential component. If a ′ ⩽ 2 a , the pair interactions reduce themselves to nearest neighbours which permits a closed-form solution of thermodynamics in the isothermal–isobaric ensemble characterized by temperature T and pressure p. We focus on the equation of state (EoS) which relates the average distance between particles (reciprocal density) l to T and p ⩾ 0 . The EoS is expressible explicitly in terms of elementary or special functions for specific, already known and new, cases like the square shoulder, the linear and quadratic ramps as well as certain types of logarithmic interaction potentials. The emphasis is put on low-T anomalies of the EoS. Firstly, the equidistant ground state as the function of the pressure can exhibit, at some ‘compressibility’ pressures, a jump in chain spacing from a′ to a. Secondly, the analytical structure of the low-T expansion of l ( T , p ) depends on ranges of p-values. Thirdly, the presence of the NTE anomaly depends very much on the shape of the core-softened potential.

Dynamics and dissipation in 2D fluid foams: The foamy continuum model

The paper establishes the governing equations of the dynamics of a foamy continuum , in the sense of Davini and Podio-Guidugli, which is expected to mimic the behavior of a monodisperse fluid foam. We model this special continuum as a dissipative ordered fluid, following the lead by Sonnet and Virga. Attention to both regular and topological transformations is taken.

Collision/no-collision results of a solid body with its container in a 3D compressible viscous fluid

Collision/no-collision results of a solid body with its container in a 3D compressible viscous fluid

The electro-hydrodynamic force evolution in cross field pin to plate discharge with different voltage polarity

This paper presents experimental observations and simulation results on the interaction between plasma and gas flow in pin-to-plate corona discharge under different voltage polarities. Schlieren experiments reveal that during a single discharge process, only a unidirectional electro-hydrodynamic (EHD) force toward the plate electrode is observed in positive corona discharge, while an additional scope of EHD force toward the pin electrode is found in negative corona discharges. Similarly, this phenomenon can be observed in a 2D fluid model simulation that disregards any disturbance to helium gas during transient discharging development. The evolution of EHD force follows a similar pattern as the discharge itself, which can be divided into three stages. The EHD force is scarcely observed during the dissipation stage. During the development stage, an EHD force toward the pin electrode is generated as the streamer approaches the plate electrode. In the stable stage following a complete discharge, EHD forces toward both electrodes are observed, with a spatial distribution structure of centrosymmetry presented in positive corona discharges. However, in negative cases, the EHD force toward the pin electrode is significantly smaller than that toward the other electrode. Through the analysis of spatial and temporal distribution of charged particles, it is determined that O2+ ions play a predominant role in generating the EHD force directed toward the pin electrodes in negative corona discharges. The reversal of local net charge polarity caused by Penning ionization and attachment reactions producing negative ions further enhances this effect in negative corona discharges, thereby highlighting the polarity differences.

Distribution of H− ions in RF negative hydrogen ion source obtained based on their volume and surface production processes

Abstract The radio frequency (RF) negative hydrogen ion source is employed in neutral beam injection (NBI) system for magnetic confined fusion devices. To satisfy the required beam current of negative hydrogen ions in NBI for fusion, the surface production on the plasma grid (PG) surface is introduced to increase the amount of negative hydrogen ions. In this paper, a 2D fluid model is established, including volume production and surface production of negative hydrogen ions. This work focuses on the spatial distributions of negative hydrogen ions with different gas pressures, PG bias potentials, magnetic filter filed (MFF) positions and RF powers. The results show that the density of negative hydrogen ions is enhanced by the surface production. As the gas pressure increases, the increase in the negative hydrogen ion density is dominated by the increase in the conversion of neutral hydrogen atoms at the PG surface. As the bias potential increases, the distribution of negative hydrogen ions is slightly shifted towards the PG due to the reduction of electric field near the PG. As the MFF position shifts towards the PG, the increase in the negative hydrogen ion density is dominated by the increase in the conversion of positive hydrogen ions at the PG surface. Moreover, the negative hydrogen ion density increases with the increased RF power, which is dominated by the increase in the conversion of positive hydrogen ions at the PG surface. The model facilitates the understanding of the negative hydrogen ion distribution and the optimization of negative hydrogen ion production.

Study on the influence of temperature on positive streamer under sub-atmospheric pressure

Abstract Electrified transportations are playing more important role during the sustainable development of society, while much more complex environment, such as gas discharge in high altitude, should be considered for the outdoor high voltage insulation safety. The ambient air pressure and temperature are both recognized as significant factors in the streamer dynamics. Herein we established a 2D fluid plasma chemical model with a 5 mm rod-plate gap to explore streamer propagation in air at 50 kPa, 233–353 K. Under sub-atmospheric pressure, temperature increases from 233 K to 353 K accelerate charged particle movement, enhancing streamer velocity and radius. Meanwhile, temperature affects the ionization process. Rising temperature increases electron density in the streamer channel but reduces electric field strength at the streamer head. This study systematically investigates how electron transport coefficients, mean electron energy, space charge and effective ionization coefficients influence streamer discharge. It is observed that, in contrast to atmospheric pressure, the evolution of space charge shows an inverse trend, showing reduced space charge with rising temperature. These findings enhance understanding of sub-atmospheric streamer behavior and establish theoretical foundations for evaluating high-altitude high-voltage system insulation.

On the mathematical modelling of 2D fluid foams

Abstract Fluid foams are two-phase fluids with a great variety of textures which may change during their deformation processes. Their continuum mechanical modelling is made problematic by the difficulty of individuating what to regard as a material point. In Part 1, the simplest shearing motion of a monodisperse, close-packed, two-dimensional fluid foam is here revisited. In Part 2, the notion of a foamy continuum, that is, an ordinary continuum body imitating the foam’s behaviour, is introduced. The final section contains a brief discussion of the thermodynamics of a shear deformation process involving a topological change of texture.

Effects of Pore‐Scale Three‐Dimensional Flow and Fluid Inertia on Mineral Dissolution

AbstractMineral dissolution releases ions into fluids and alters pore structures, affecting geochemistry and subsurface fluid flow. Thus, mineral dissolution plays a crucial role in many subsurface processes and applications. Pore‐scale fluid flow often controls mineral dissolution by controlling concentration gradients at fluid‐solid interfaces. In particular, recent studies have shown that fluid inertia can significantly affect reactive transport in porous and fractured media by inducing unique flow structures such as recirculating flows. However, the effects of pore‐scale flow and fluid inertia on mineral dissolution remain largely unknown. To address this knowledge gap, we combined visual laboratory experiments and micro‐continuum pore‐scale reactive transport modeling to investigate the effects of pore‐scale flow and fluid inertia on mineral dissolution dynamics. Through flow topology analysis, we identified unique patterns of 2D and 3D recirculating flows and their distinctive effects on dissolution. The simulation results revealed that 3D flow topology and fluid inertia dramatically alter the spatiotemporal dynamics of mineral dissolution. Furthermore, we found that the 3D flow topology fundamentally changes the upscaled relationship between porosity and reactive surface area compared to a conventional relationship, which is commonly used in continuum‐scale modeling. These findings highlight the critical role of 3D flow and fluid inertia in modeling mineral dissolution across scales, from the pore scale to the Darcy scale.

Impact of Post-Percutaneous Coronary Intervention Quantitative Flow Ratio of De Novo Coronary Artery Lesions Treated with Drug-coated Balloons: The QUADRIC Study

Background: Quantitative flow ratio (QFR) is a non-invasive modality that uses 3D coronary artery reconstruction and coronary fluid dynamics to estimate fractional flow reserve. The Quantitative Flow Ratio of De Novo Coronary Artery Lesion Treated with Drug-Coated Balloon (QUADRIC) study aims to assess the role of QFR in predicting major adverse cardiovascular events (MACE) in de novo coronary lesions treated with drug-coated balloons (DCBs). Methods: This study is an investigator-initiated real-world study involving 414 patients and 429 lesions. Patients aged 18 years and above who were admitted between January 2020 and December 2020 for percutaneous coronary intervention (PCI) with a DCB in a de novo lesion were included. The primary outcome was two-year MACE rate, and the secondary outcome was the clinically driven target lesion revascularisation rate at 24 months. Results: The mean age of patients was 61 years [SD 10.1]. In total, 234 (79.6%) patients were men, 188 (63.9%) had diabetes and 163 (55.4%) presented with acute coronary syndrome. The mean estimated lesion length was 32 mm (SD 20.1) and the mean vessel size was 2.5 mm (range: 2.0–4.0 mm; SD 0.4). The 2-year primary endpoint occurred in 8 (4.5%) patients in the QFR ≥0.90 group and in 14 (12.6%) patients in the QFR <0.90 group (p=0.011). Post-PCI QFR was significantly lower in patients with target lesion revascularisation during follow-up compared to those without it (p=0.032). Conclusion: In this study, a post-PCI QFR <0.90 could be used to predict MACE events in patients with de novo coronary artery lesions treated with DCB and improve patient outcomes within the first two years. However, a larger randomised trial is recommended.

Boundary Flow-Induced Membrane Tubulation Under Turgor Pressures.

During clathrin-mediated endocytosis in yeast cells, a small patch of flat membrane is deformed into a tubular shape. It is generally believed that the tubulation is powered by actin polymerization. However, studies based on quantitative measurement of the actin molecules suggest that they are not sufficient to produce the forces to overcome the high turgor pressure inside of the cell. In this paper, we model the membrane as a viscous 2D fluid with elasticity and study the dynamic membrane deformation powered by a boundary lipid flow under osmotic pressure. We find that in the absence pressure, the lipid flow drives the membrane into a spherical shape or a parachute shape. The shapes over time exhibit self-similarity. The presence of pressure transforms the membrane into a tubular shape that elongates almost linearly with time and the self-similarity between shapes at different times is lost. Furthermore, the width of the tube is found to scale inversely to the cubic root of the pressure, and the tension across the membrane is negative and scales to the cubic root squared of the pressure. Our results demonstrate that boundary flow powered by myosin motors, as a new way to deform the membrane, could be a supplementary mechanism to actin polymerization to drive endocytosis in yeast cells.

Dynamic study of streamer interaction with fluidized particles in a plasma fluidized-bed system

Exploration of the interaction dynamics between plasma and fluidized particles in a plasma fluidized-bed holds practical importance for elucidating the mechanism of plasma treatment of powders. In this study, we employed a 2D fluid model to investigate the effects of particle diameter, dielectric constant, and inter-particle spacing, with the primary aim of simulating the specific consequences of variations in particle size, material type, and gas-to-powder ratio (GPR) on the powder processing effect. The results indicate that particles with diameters below 300 μm exert less impact on streamer propagation, enabling complete plasma wrapping of the particle surface (100%). However, particles with a diameter of 400 μm induce branching, leading to a reduction in the treatment area to 46%. These observations imply a critical particle size range of 300–400 μm for achieving effective plasma treatment of the fluidized particles. Plasma treatment ensures a comprehensive surface coverage on particles with low dielectric constants (εr<4), while particles possessing a higher dielectric constant (εr>8) exhibit a diminished plasma-treated surface area (80%), meaning that longer treatment durations for high dielectric constant materials may be required to achieve a comparable treatment effect. Furthermore, as the inter-particle spacing increases from 10 to 500 μm, the plasma-treated surface area undergoes an initial increment, followed by a subsequent reduction. Notably, at 300 μm spacing, the streamer channel displays a root-like branching pattern, leading to a substantial expansion of the plasma-treated surface area. This indicates that an optimal GPR in the fluidized-bed system can enhance the powder treatment effect.

Discovery of discretized differential equations from data: Benchmarking and application to a plasma system

This study presents and evaluates Phi Method, a novel data-driven algorithm designed to discover discretized differential equations governing dynamical systems from data. Phi Method employs a constrained regression on a library of candidate terms to develop reduced-order models (ROMs) capable of accurate predictions of systems' state. To validate the approach, we first benchmark Phi Method against canonical dynamical systems governed by ordinary differential equations, highlighting the strengths and limitations of our approach. The method is then applied to a 2D fluid flow problem to verify its performance in learning governing partial differential equations (PDEs). The fluid flow test case also underlines the method's ability to generalize from transient training data and examines the characteristics of the learned local operator in both basic and parametric Phi Method implementations. The approach is finally applied to a 1D azimuthal plasma discharge problem, where data are now generated from a kinetic particle-in-cell simulation that does not explicitly solve the governing fluid-like equations. This application aims to demonstrate Phi Method's ability to uncover underlying dynamics from kinetic data in terms of optimally discretized PDEs, as well as the parametric dependencies in the discharge behavior. Comparisons with another ROM technique—the optimized dynamic mode decomposition—for the plasma test case emphasize Phi Method's advantages, mainly rooting in its ability to capture local dynamics with interpretable coefficients in the learned operator. The results establish Phi Method as a versatile tool for developing data-driven ROMs across a wide range of scenarios.

Suboptimal Fluid Antenna Systems for Maximizing the Secrecy Rate with Untrusted Relays

This research examines the effectiveness of untrusted relays in fluid antenna-assisted communication systems subjected to arbitrary correlated fading channels. The transmitter is represented to share confidential information to a legitimate receiver,both utilizing a 1D Fluid Antenna System (FAS), while an untrusted relay, equipped with a fixed antenna, attempts to decrypt the intended message. In this case, cooperative jamming is adopted and we jointly optimize the power allocation of the transmitted jamming signal and the FAS beamforming weights to maximize the secrecy rate. Due to the non-convex nature of the optimization issue, we employ the Particle Swarm Optimization (PSO) approach to get the suboptimal secrecy rate. Ultimately, numerical results demonstrate that the use of FAS ensures more safe and reliable transmission, while an increase in FAS components produces more focused beams. This leads to improved alignment of the broadcast signal toward the legitimate receiver, increasing the necessary signal intensity while reducing leakage to unauthorized relays.

Non-self-similar collapse of three point vortices in a generalized two-dimensional fluid system

Abstract In this study, we investigate the non-self-similar collapse of three vortices in a point vortex model of a generalized two-dimensional (2D) fluid system. In the classical point vortex model, the existence of the self-similar collapse of three vortices has been well known from Gröbli (1877 Vierteljahresschr. Naturforsch. Ges. Zürich 22 129). Moreover, the non-existence of the non-self-similar collapse of three vortices in the classical point vortex model was proved by Hernández–Garduño and Lacomba (2007 J. Math. Fluid Mech. 9 75) and Hiraoka (2008 Nonlinearity 21 361). In this study, we apply a method similar to that of former authors to the point vortex model of the generalized 2D fluid system, which includes a real parameter α, where 0 < α ⩽ 3 . We present proofs for the possible existence of the non-self-similar collapse of three vortices for 0 < α < 2 and for the non-existence of such collapse for 2 < α ⩽ 3 . Furthermore, as an application, we analyze in detail the self-similar and non-self-similar collapses of three point vortices in the symmetric case of the surface quasi-geostrophic system (α = 1). A close relationship between the self-similar and non-self-similar collapses of the three vortices is identified.

Analytical solution for the hydrodynamic resistance of a disk in a compressible fluid layer with odd viscosity on a rigid substrate.

Chiral active fluids can exhibit odd viscosity, a property that breaks the time-reversal and parity symmetries. Here, we examine the hydrodynamic flows of a rigid disk moving in a compressible 2D fluid layer with odd viscosity, supported by a thin lubrication layer of a conventional fluid. Using the 2D Green's function in Fourier space, we derive an exact analytical solution for the flow around a disk of arbitrary size, as well as its resistance matrix. The resulting resistance coefficients break the Onsager reciprocity, but satisfy the Onsager-Casimir reciprocity to any order in odd viscosity.

3D Convective Urca Process in a Simmering White Dwarf

Abstract A proposed setting for thermonuclear (Type Ia) supernovae is a white dwarf that has gained mass from a companion to the point of carbon ignition in the core. In the early stages of carbon burning, called the simmering phase, energy released by the reactions in the core drive the formation and growth of a core convection zone. One aspect of this phase is the convective Urca process, a linking of weak nuclear reactions to convection, which may alter the composition and structure of the white dwarf. The convective Urca process is not well understood and requires 3D fluid simulations to properly model the turbulent convection, an inherently 3D process. Because the neutron excess of the fluid both sets and is set by the extent of the convection zone, the realistic steady state can only be determined in simulations with real 3D mixing processes. Additionally, the convection is relatively slow (Mach number less than 0.005) and thus a low Mach number method is needed to model the flow over many convective turnovers. Using the MAESTROeX low Mach number hydrodynamic software, we present the first full-star 3D simulations of the A = 23 convective Urca process, spanning hundreds of convective turnover times. Our findings on the extent of mixing across the Urca shell, the characteristic velocities of the flow, the energy-loss rates due to neutrino emission, and the structure of the convective boundary can be used to inform 1D stellar models that track the longer-timescale evolution.

Stabilization of loosely coupled schemes for 0D–3D fluid–structure interaction problems with application to cardiovascular modelling

In this paper we analyze the numerical oscillations affecting loosely coupled schemes for hybrid-dimensional 0D–3D fluid–structure interaction (FSI) problems, which arise e.g. in the field of cardiovascular modeling, and we propose a novel stabilized scheme that cures this issue. We study several loosely coupled schemes, including the Dirichlet–Neumann (DN) and Neumann–Dirichlet (ND) schemes. In the first one, the 0D fluid model prescribes the pressure to the 3D structural mechanics model and receives the flow. In the second one, on the contrary, the fluid model receives the pressure and prescribes the flow. The terms DN and ND, employed in the FSI literature, are borrowed from domain decomposition methods, although here a single iteration is performed before moving on to the next time step (that is, the coupling is treated explicitly). Should the fluid be enclosed in a cavity, the DN scheme is affected by non-physical oscillations whose origin lies in the balloon dilemma, for which we provide an algebraic interpretation. Moreover, we show that also the ND scheme can be unstable for a range of parameter choices. Surprisingly, increasing either the viscous dissipation or the inertia of the structure favours the onset of oscillations and, for certain parameter choices, the ND is unconditionally unstable. In the presence of inertial terms, by reducing the time step size below a certain threshold, the amplitude of the numerical oscillations is even amplified. We provide an explanation for these facts and establish sharp stability bounds on the time step size. Our analysis extends to Robin–Robin schemes, based on linear combinations of the conditions of pressure continuity and either volume or flux continuity. While appropriate choices of Robin coefficients can achieve numerical stability, tuning these coefficients can be challenging in practice. To address these issues, we propose a numerically consistent stabilization term for the Neumann–Dirichlet scheme, inspired by physical insight on the onset of oscillations. We prove that our proposed stabilized scheme is absolutely stable for any choice of time step size. Notably, the proposed scheme does not require parameter tuning. These results are verified by several numerical tests. Finally, we apply the proposed stabilized scheme to an important problem in cardiac electromechanics, namely the coupling between a 3D cardiac model and a closed-loop lumped-parameter model of blood circulation. In this setting, our proposed scheme successfully removes the non-physical oscillations that would otherwise affect the numerical solution.

UTILIZATION OF HEC-RAS 2D FOR FLOOD INFLUENCE MODELING DUE TO PEAK DISCHARGE OF WALANAE RIVER IN WAJO DISTRICT

On December 25, 2024, a flood disaster struck Sabbangparu Sub-district, Wajo Regency, South Sulawesi, caused by heavy rains that persisted for several days. This led to the overflow of the Walanae River and additional flooding from neighboring regencies. The disaster affected thousands of residents, submerged agricultural lands, and completely cut off several access roads. This study conducted a simulation aimed at predicting flood-affected areas due to the overflow of the Walanae River in Wajo Regency as part of future disaster mitigation efforts. The simulation utilized HEC-RAS 6.4.1 software, which has the capability to model 1D and 2D fluid flow. Additionally, flood-affected area analysis was performed using ArcGIS 10.8. The flood map simulation results indicated that the affected area covered 10,814.35 hectares, equivalent to 68.22% of the administrative area of Sabbangparu Sub-district. The river cross-section simulation revealed that most of the Walanae River cross-sections were unable to accommodate the peak discharge of 3,658.4 m³/s, causing water to overflow into residential areas and rice fields. This poses the risk of significant economic losses and even fatalities. The results of this study are expected to serve as a reference in planning future flood disaster mitigation efforts.

Discontinuous Structural Transitions in Fluids with Competing Interactions.

This paper explores how competing interactions in the intermolecular potential of fluids affect their structural transitions. This study employs a versatile potential model with a hard core followed by two constant steps, representing wells or shoulders, analyzed in both one-dimensional (1D) and three-dimensional (3D) systems. Comparing these dimensionalities highlights the effect of confinement on structural transitions. Exact results are derived for 1D systems, while the rational function approximation is used for unconfined 3D fluids. Both scenarios confirm that when the steps are repulsive, the wavelength of the oscillatory decay of the total correlation function evolves with temperature either continuously or discontinuously. In the latter case, a discontinuous oscillation crossover line emerges in the temperature-density plane. For an attractive first step and a repulsive second step, a Fisher-Widom line appears. Although the 1D and 3D results share common features, dimensionality introduces differences: these behaviors occur in distinct temperature ranges, require deeper wells, or become attenuated in 3D. Certain features observed in 1D may vanish in 3D. We conclude that fluids with competing interactions exhibit a rich and intricate pattern of structural transitions, demonstrating the significant influence of dimensionality and interaction features.