Interface Motion Research Articles

A new ghost-cell/level-set method for three-dimensional flows

This study presents the implementation of a tailored ghost cell method in Hydro3D, an open-source large eddy simulation (LES) code for computational fluid dynamics based on the finite difference method. The former model for studying the interaction between an immersed object and the fluid flow is the immersed boundary method (IBM) which has been validated for a wide range of Reynolds number flows. However, it is challenging to ensure no-slip and zero gradient boundary conditions on the surface of an immersed body. In order to deal with this, a new sharp-interface ghost-cell method (GCM) is developed for Hydro3D. The code also employs a level-set method to capture the motion of the air-water interface and solves the spatially filtered Navier-Stokes equations in a Cartesian staggered grid with the fractional step method. Both the new GCM and IBM are compared in a single numerical framework. They are applied to simulate benchmark cases in order to validate the numerical results, which mainly comprise single-phase flow over infinite circular and square cylinders for low- and high-Reynolds number flows along with two-phase dam-break flows with a vertical cylinder, in which a good agreement is obtained with other numerical studies and laboratory experiments.

Effects of global and climate change on the freshwater-seawater interface movement in a Mediterranean karst aquifer of Mallorca Island

Karst aquifers are globally prized freshwater sources, posing a significant preservation challenge. These aquifers typically exhibit dual or even triple porosities, encompassing matrix, fractures-fissures and conduits, rendering them highly responsive to variations in chemical characteristics and hydraulic head. In coastal regions, these aquifers often possess extensive subsurface conduit networks intricately linked to the rock matrix, facilitating groundwater discharge into the sea. Therefore, they display acute sensitivity to seawater intrusion, swiftly reacting to changes in precipitation and pumping regimes. This makes them exceptionally vulnerable to short-term meteorological fluctuations and long-term climate change. Their high heterogeneity leads to uneven penetration of the freshwater-seawater interface, causing rapid seawater intrusion inland over significant distances. The Mediterranean region, characterized by water deficit and water stress, faces strong impacts from climate change, featuring a warming atmospheric trend exceeding the global average, along with diminished rainfall exacerbating water scarcity. Increasing water demands for agriculture, urban development, and the growing tourism industry, because of global change, are worsening water stress. Our primary research objectives were analyzing the environmental consequences of global and climate change on seawater intrusion in Mediterranean coastal karst aquifers, with a focus on the role of the double-flow model, thus contributing to the understanding of the processes involved. To achieve this, we selected a study region on Mallorca Island in the western Mediterranean, where a karst aquifer system discharges into the sea. We employed various study methods, notably hydrochemical techniques and multi-isotopic analysis, encompassing the examination of 2H and 18O isotopes in water, 87Sr/86Sr ratio, Sr and B concentrations, and δ11B in water. A key finding is the rebound effect, wherein aquifers recontaminate due to solute molecular back-diffusion following cessation of extractions and the retreat of marine intrusion, providing insight into the impact of climate and global change on Mediterranean karst aquifers.

Effects of carbon nanotube addition on the microstructures, martensitic transformation, and internal friction of Cu–Al–Ni shape-memory alloys

In this study, we analyze the influences of carbon nanotube (CNT) addition on the martensite transformation and internal friction of Cu–Al–Ni shape-memory alloys (SMAs). X-ray diffraction and differential scanning calorimetry results demonstrate that Cu–13.5Al–4Ni–xCNT (x = 0, 0.2, 0.4, 0.6, and 0.8 wt%) SMA/CNT composites exhibit a β1(DO3)⇄β1′(18R)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\upbeta }_{1}({\\mathrm{DO}}_{3})\\rightleftarrows {\\upbeta }_{1}^{\\mathrm{^{\\prime}}}(18\\mathrm{R})$$\\end{document} martensitic transformation. The martensitic transformation temperatures and transformation enthalpies of the martensitic transformation peaks for the Cu–13.5Al–4Ni–xCNT (x = 0–0.8 wt%) composites gradually decrease with the increase in the amount of CNT addition. Compared to the Cu–13.5Al–4Ni SMA, the Cu–13.5Al–4Ni–xCNT (x = 0.2–0.8 wt%) SMA/CNT composites exhibit significant improvements in the amount of dissipation of energy (storage modulus (E′))\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${E}^{\\prime}))$$\\end{document} and mechanical strength. However, the tan δ of the internal friction peak gradually decreases with the increase in the CNT content above 0.6 wt%. The reduction in tan δ is attributed to the decrease in the magnitude of the austenite-to-martensite transformation and precipitation of γ2 (Cu9Al4) phase particles, which impede the interface motion in between the parent/martensitic phase and martensitic phase.

A numerical model for simulation of two-phase flows interaction with flexible slender bodies

This paper introduces a fluid–structure interaction (FSI) model for simulation of the coupled dynamics between two-phase flows and elastic slender structures. This model is extended from the early FSI model for single-phase flows by Wang et al. [“A coupled flow and beam model for fluid–slender body interaction,” J. Fluids Struct. 115, 103781 (2022)] to two-phase flows with interfaces of two liquids or free surfaces between gas and liquid. To better capture the interface movement of the two-phase flows and the interaction with the deformable structure, a consistent mass and momentum flux scheme is developed to reduce the spurious oscillation of fluid velocities near the interface, especially in the lower density (e.g., air) region. The proposed model is validated by a series of two-dimensional laboratory experiments of flow impact on a deformable plate, demonstrating that the model has good capabilities of conserving mass and momentum during the process of plate deformation by impulsive flow forces. The model is also applied to the investigation of three-dimensional dam break flow impact on a column of elastic plates. The complex interaction between the plates and the flow is discussed based on the simulation results.

Interfacial particle motion by dielectrophoretic force

Direct numerical simulations of motion of an interfacial two-dimensional cylinder under the effect of the dielectrophoretic force in an electric field are conducted and the performance of the vertical force balance and the horizontal motion is investigated. The influence of important factors (contact angle, viscosity ratio, permittivity, particle density and radius) on the velocity is studied. Results show that different particle densities and viscosity ratios tend to change the magnitude of drag force and different contact angles, fluid medium permittivities, particle permittivities and particle radii tend to change the magnitude of dielectrophoretic force, which leads to influence the velocity of interfacial particle motion. This work innovatively applies the dielectrophoretic force to drive interfacial particle motion. We hope this work may provide an advanced method for efficient and contactless removal of particle contaminations at fluid interfaces by means of dielectrophoresis. Our study may provide a new efficient method for actively transporting and separating interfacial particles and pave the way to the research about the interaction of dielectric particles floating on fluid interfaces instead of suspending in fluid medium. The dielectrophoresis may contribute to the development of driving technology for microrobots attached to fluid interfaces.

Nonlinear EHD stability of a cylindrical interface separating two Rivlin-Ericksen fluids: A novel analysis

The NS of a cylindrical interface separating two liquids of the RE type is scrutinized in the present article. Through the presence of uniform streaming, the two electrified liquids are acted upon by an unchanged longitudinal EF. Density, viscoelasticity, and electrical features of the two liquids are all diverse; the ST at the interface is maintained. The motivation behind the present study lies in the numerous potential applications of this topic in manufacturing, engineering, and practical physics. The viscoelastic participation, also recognized via the VPF, can merely be constructed at the interface owing to the complexity of the theoretical process. The GEMs are inspected by the LS approach, then the nonlinear BCs are reached. A nonlinear equation of the interface movement is created by this technique. As well-known, the LS performance was extensively discussed in numerous publications. Accordingly, we exclusively study the nonlinear intelligence in the present work. A new methodology grounded in the NPA is employed to scrutinize the interface deviation in numerous frameworks and to estimate the NS. The last equation is an instance of a PDE with composite quantities. This equation is signified as a nonlinear HRHO, subject to specific constraints. A linear equation that corresponds to the measured NPA is created. The two equations are confirmed by a numerical analogous. At this stage, the linear equation is established to investigate the framework of a liquid flow along with the dimensionless fundamental numerals. Numerous non-dimensional physical numbers, used to characterize the system, are likewise determined. The physical significance of certain amounts aids in certain physical explanations. A set of charts is adopted to theoretically inspect and numerically display of the stability thresholds. The apprehension of instability/stability is portrayed by organizing the EF strength against the travelling wave numeral. To validate the stability profile, several polar representations are depicted. In our opinion, the current analysis is simple, operative, hopeful, and may be employed in a diversity of circumstances.

A pressure Poisson equation-based second-order method for solving two-dimensional moving contact line problems with topological changes

We develop a second-order Cartesian grid based numerical method to solve two-dimensional moving contact line problems, which are modeled by the incompressible Navier–Stokes equations with the Navier-slip condition and the contact angle condition (CAC). The solutions of the flow field and the interface motion are decoupled in an alternating way. For a given interface, the velocity field is solved via a pressure Poisson equation formulation of the incompressible Navier–Stokes equations, which is numerically discretized by the immersed interface method. Once the velocity field is obtained, the interfacial kinematics together with the CAC is reformulated into a variational system, which is solved by the parametric finite element method (FEM). With this hybrid method, we detect topological changes in the interface by the inconsistency of neighboring normal vectors, which are directly computed through the parametric FEM. Second-order accuracy of the proposed method in both the interface and the contact line positions before and after topological changes has been numerically validated. Moreover, with the help of the numerical method, the merging and collision dynamics of droplets on the substrates are easily investigated.

Electrokinetic Effect of a Two-Liquid Interface within a Slit Microchannel.

This paper presents an investigation of the electrokinetic effect at a two-liquid (immiscible liquid-aqueous solution) interface within a slit microchannel using a three-dimensional (3D) numerical model, with a particular focus on the impact of the surface ζ-potential and liquid phase height on the interface electrokinetic velocity. The findings indicate that the direction of the interface movement depends on the ζ-potentials at the two-liquid interface and the microchannel wall. When the absolute value of the negative ζ-potential at the interface is smaller than that at the wall, the interface moves toward the negative pole of the applied direct current (DC) electric field; conversely, it moves in the opposite direction. The velocity of interface motion decreases as the height of the aqueous phase and the dynamic viscosity ratio between the immiscible liquid and the aqueous solution increase. Conversely, the velocity increases with an elevation in the height of the immiscible liquid phase and the DC electric field intensity. This study holds significant importance in elucidating the patterns of change in fluid interface electrokinetic effects and their potential applications in manipulating and separating particulate pollutants within water systems.

The effect of flame curvature and flame base movement on the frequency response of a conical Bunsen flame

We create a general model for the tracking of a premixed flame sheet. This model is based on a Lagrangian formulation of the interface motion, which is more computationally efficient than the level-set formulation solved on a grid. We apply this model to a conical Bunsen flame in which flame-base oscillations and flame stretch effects are also considered. We demonstrate that the flame-front dynamics, the heat release rate perturbations, and the flame transfer function (FTF) are affected by three features: (i) the velocity field locally perturbing the flame-front, (ii) the flame-base oscillations normal to the steady flame-front propagating along the flame and (iii) the flame-base oscillations tangential to the flame-front reducing and increasing the flame-length. We provide a physical explanation for the saturation of the FTF phase shift with increasing forcing frequency, which is found experimentally. We show why a n−τ model with fixed τ cannot model this simple flame and that, when building a quantitatively-accurate model of a thermoacoustic system containing this flame, the flame dynamics need to be simulated directly or modelled more accurately than with the n−τ model. The flame model used in this paper has been designed to be differentiable so that it can be used for rapid data assimilation using Laplace’s method. Code is provided so that the user can generate the FTF of a conical premixed flame with any set of parameters and any flame-base trajectory.

Research of thermoelectric null-thermostat

Objective. The purpose of the study is to develop and study the design of a thermoelectric null-thermostat, characterized by low power consumption, in which high accuracy of temperature stabilization of the reference junctions of differential thermocouples is achieved by placing them directly near the water-ice interface.Method. The study was carried out on an experimental model of a thermoelectric null-thermostat. To study heat transfer processes, visual observation of the movement of the ice-water interface in the null-thermostat chamber was carried out. Temperature values were recorded at the lower and upper bases of the chamber, as well as at the hot and cold junctions of the thermoelectric module (TEM) using thermocouples.Result. The dependences of the change in temperature of the upper and lower base of the working chamber, as well as the phase boundary over time, the duration of time for complete ice penetration on the TEM supply current, and the temperature difference, respectively, between the surface of the cold junction of the TEM and the lower base of the working chamber were obtained , the surface of the hot junction of the thermal module and the upper base of the working chamber.Conclusion. It has been established that the speed of movement of the phase boundary strongly depends on the value of the supply current of the thermoelectric battery, which corresponds to the heat flow at the upper and lower base of the working chamber. As follows from the data presented, the change in temperature of the upper base is more noticeable than the lower one. At a current of 2, 4 and 6 A, the speed of movement of the phase boundary is 0.007 m/h, 0.01 m/h and 0.013 m/h, respectively. In this case, the duration of complete melting of ice, corresponding to the duration of operation of the null thermostat, when the TEM supply current changes from 2 to 7 A, is reduced from 1,91⋅104 s to 1,38⋅104.

Experimental study on axial self-propagation of heat transfer deterioration of near-critical carbon dioxide at low mass fluxes

Near-critical CO2 exhibits unique boiling heat transfer behavior due to its high saturated vapor density, low latent heat, and extremely low surface tension. In this study, an experimental investigation was conducted to study the heat transfer deterioration of near-critical CO2 inside a vertical circular channel at low mass fluxes. The experimental results show a rapid rise in wall temperature at the outlet side with minimal power increase (∆ power = 33 W), and the wall temperature rise continuously self-propagates toward the inlet side. The heat transfer deterioration mechanism responsible for the wall temperature rise was considered to be a departure from nucleate boiling type boiling crisis based on the low vapor quality of the bulk fluid. In addition, the evolution of the axial heat transfer deterioration was analyzed in detail. And a phenomenological model was developed to explain the axial self-propagation of heat transfer deterioration based on the low mass fluxes and unique bubble behavior resulting from the low surface tension, high vapor density and low latent heat of the near-critical CO2. The model was validated using different dry/wet interface movement speeds.

Simulation of solidification microstructure evolution of 316L stainless steel fabricated by selective laser melting using a coupled model of smooth particle hydrodynamics and cellular automata

Selective Laser Melting (SLM) is an efficient and advanced manufacturing technology that utilizes lasers to melt and solidify metal or alloy powders, layer by layer, to form the desired object shape. This study aims to investigate the evolution behavior of the solidification microstructure during the SLM process and presents a novel numerical simulation method based on the Smoothed Particle Hydrodynamics-Cellular Automaton (SPH-CA) coupling model. The SPH-CA coupling model combines the particle information, such as position and temperature, from Smoothed Particle Hydrodynamics (SPH) with the Cellular Automaton (CA) method in a one-way coupling manner, enabling simultaneous computation of multiple physical fields, including heat transfer, melting, solidification, and morphology. This model addresses challenges that are difficult to handle in grid-based computations, such as free surface variations, boundary deformations, interfacial motion, and large deformations. Additionally, it effectively simulates the morphology of the solidification microstructure. Furthermore, the coupling process performs kernel function weighted calculations at the same scale, which results in higher accuracy compared to the grid-based multiscale mapping. The simulation results demonstrate that different processing parameters influence the morphology of the molten pool and the thermal undercooling, thereby affecting the growth characteristics of the grains. A higher laser scanning speed leads to smaller molten pool size, finer grain sizes in the solidification microstructure, larger laser grain angles, and a higher content of columnar grains. These findings are consistent with experimental observations and existing conclusions, providing evidence for the feasibility and effectiveness of the proposed model in the context of SLM.

Controlling the Motion of Interfaces in Capillary Channels with Non-uniform Surface Wettability

The use of self-driven flows in microfluidic devices attracts many researchers as the external flow-driving mechanism is diminished or eliminated. One of the mechanisms providing such motions is generating a pressure difference across interfaces as in the case of the motion in capillary tubes. The capillarity, namely, the pressure difference across the interface due to its curvature drives the motion. This pressure depends on the interaction with the capillary walls and is controlled if one varies the surface energy of the walls. In this study, we search for the effects of surface energy on the motion of interfaces in capillary-driven flow. To this end, we model the motion of fluid particles in a capillary channel and integrate the governing equations using the binary lattice Boltzmann method for the two-phase flow. We, first, validate our solver for canonical static and dynamic problems. We, then, discuss two main contributions; we show how to deviate the interface speed from the ones moving in channels with uniform wall energies and discuss the conditions under which such an interface stagnates (like a passive valve in a channel). Tuning the wettability of the channel walls, we provide a simple condition for stopping the interface: the summation of the equilibrium contact angles interface make with the channel walls at the bottom and top wall need to satisfy $\theta_{eq}^{top}+\theta_{eq}^{bot} \geq \pi$. Configurations and wetting properties of different wettability regions play major roles together

Simulation study of nucleation mechanism of grown-in dislocations near grain boundary during solidification of silicon

We carried out molecular dynamics (MD) simulations of directional solidification of silicon with carbon impurity to study the nucleation mechanism of grown-in dislocations near Σ27 grain boundary. We find that carbon impurity atoms segregate to crystal boundary groove. A stacking fault composed of two consecutive {111} bi-layer plane twinnings nucleates near the carbon segregation site in the grain boundary groove. Then Shockley partial dislocations composed of 5-5-8-atom rings are formed between stacking fault area and normal stacking area. These dislocations originate from the grain boundary, pass through the crystal, extend to the solid-liquid interface and expand with the movement of the solid-liquid interface, indicating that they are grown-in dislocations formed during the directional solidification of silicon. Our study is expected to provide a theoretical basis for further reducing the dislocation density of multicrystalline silicon (mc-Si).

Investigation of Vaned-Recessed Casing Treatment in a Low-Speed Axial Flow Compressor, Part I: Time-Averaged Results

This paper investigates the effects of two modifications to a vaned recessed casing treatment. First, the shape of a circular curve was used in the top of the treated casing. Second, a fully curved guide vane was also applied. The goals of the modifications are to enhance the flow recirculation as well as to relieve the low-speed flow, which is normally accumulated within the corners of the vaned recessed casing treatment. The solid casing in addition to the two vaned recessed configurations with 23.2% and 53.5% rotor blade tip axial chord exposure have been studied numerically. The results indicated that two mechanisms are involved in the stall margin enhancement. First, the circumferential pressure gradient is reduced for both configurations. The reduction in pressure gradient largely reduces the development of tip leakage vortex and, thus, the generation of low-speed fluid is diminished. Second, the main flow/tip leakage interface moves toward downstream and the movement of interface toward the leading edge is delayed. The second configuration with a greater rotor blade tip exposure enables extra flow recirculation due to decreasing surface area and, therefore, could be superior to the application of the first casing treatment configuration. The major streamlines within the casing treatment are also discussed. The time-averaged results are presented in this paper, while the unsteady results including instantaneous flow fields, origins of the unsteadiness and frequency analysis are discussed in part II.

Development of Coupled Numerical Model between Floating Caisson and Anti-Oscillation Tanks

Floating caissons can oscillate owing to ocean waves when towed to an installation site. To reduce these oscillations, free-surface anti-oscillation tanks mounted on floating caissons have been proposed. However, no coupled numerical model exists between the motion of the floating caisson and fluid flow in the tanks based on computational fluid dynamics (CFD). In this study, a coupled model is developed and compared to existing physical experiments for validation. In the coupled model, the vertical and rotational motion of the floating caisson are computed as a rigid body, and the motion of the free water in the tank is computed using a CFD model. Numerical results show the predictive capability of the coupled model in terms of the rotational motion (pitch) of the floating caisson within ±20% of experimental data, regardless of the absence or presence of water in the tank. The numerical results also show that the fluid flow with complex air–water interface motion in the tank can be analyzed in detail using the coupled model. This suggests that the coupled model developed in this study is a useful tool for quantitatively assessing the effectiveness of an anti-oscillation tank for reducing the pitch of a floating caisson.

Modeling the dynamic magneto-mechanical response of magnetic shape memory alloys based on Hamilton’s principle: The numerical algorithm

This paper is the second part of a variational modeling work on the dynamic magneto-mechanical response of magnetic shape memory alloys (MSMA). In the first part of this series work, the governing equations system for modeling the dynamic response of MSMA samples has been derived based on Hamilton’s principle, which contains the Maxwell’s equations, the magneto-mechanic equations, the evolution equations of internal variables and the twin interface motion criteria. In this paper, we aim to conduct comprehensive numerical simulations on the dynamic magneto-mechanical response of MSMA samples. To solve the governing system, the space–time finite element method is applied and a double-loop iterative numerical algorithm is proposed. By using this algorithm, the independent variables in the governing system and the motion of twin interfaces in the MSMA sample can be determined separately and iteratively. Besides that, a specific discretization of the sample is adopted to simplify the calculation of variant state distribution in the sample. To show the efficiency of the numerical algorithm, the magneto-mechanical response of a MSMA sample in stress-assisted dynamic field loading tests and field-assisted dynamic mechanical loading tests are studied. Based on the numerical results, some global response curves of the MSMA sample are plotted, which show good consistency with the experimental results. Furthermore, the current configuration of the sample and the distributions of some important physical fields in the sample can be simulated. The current work will be helpful for the design of novel actuators or energy harvesters with MSMA.

Substrate effects in hysteresis of microscale Ni–Mn–Sn Heusler alloy films

During martensitic phase transformations in thin films, substrates impact hysteresis by introducing an additional interface, which can inhibit martensite/austenite interface motion. In order to reduce hysteresis, we examine 2.9–14.5 μm thick Ni–Mn–Sn films, which in some cases have been delaminated from the substrates before or after annealing. We compare thermal hysteresis and defect densities at the interface. Delaminating films prior to annealing decreases hysteresis, whereas delaminating films after annealing does not significantly impact hysteresis. Substrate effects are attributed to the thermal expansion mismatch between the film and substrate, resulting in the formation of dislocations at the interface and, consequentially, an increase in frictional resistance to martensite/austenite interface motion.

Generation and Motion of Interfaces in a Mass-Conserving Reaction-Diffusion System

Generation and Motion of Interfaces in a Mass-Conserving Reaction-Diffusion System

A semi-implicit semi-Lagrangian method for simulating immersed boundary motion under high inertia and elasticity

In this paper, we present an efficient and stable fractional-step 2D immersed boundary (IB) method for solving the interaction problems between bulk fluid and elastic interface, in particular, when the fluid inertia and the interfacial elasticity are the significant factors affecting its dynamics. In myriads of real-world applications, the effects of high inertia and elasticity are dominant. So the complex fluid dynamics under such harsh conditions is an important topic in computational physics and is inherently challenging due to high computational complexity. In turn, it requires to solve the governing equations of elastic interfacial motion in an implicit manner so that more stable simulations can be performed by relaxing the Courant-Friedrichs-Lewy (CFL) condition. The contributions of the proposed approach are three folds. First, an iteration-free semi-Lagrangian method is employed in Navier-Stokes (NS) equations. Second, the elastic force acting along the interface is treated semi-implicitly in IB formulations. Both approaches improve the numerical stability associated with the high fluidic inertia and interfacial elasticity. Finally, to solve the resulting linear system, our novel idea is to transform the original 3-by-3 block matrix system into a reduced 2-by-2 block matrix system using a discrete projection operator in a staggered grid, and then explicitly represent the exact solution via the Schur complement of the Helmholtz operator. Owing to this feature, we refer to this proposed approach as reduced immersed boundary method (rIBM). We show that the two systems are equivalent in theory, whereas the conventional immersed boundary projection method (IBPM) modifies the discrete momentum equation in the original system. A series of numerical tests is conducted to confirm the stability of the rIBM using relatively larger time-step sizes, specifically with Reynolds number and inverse capillary number equal to or larger than approximately 1000. By estimating the computational time, the numerical efficiency of the proposed method is further verified in comparison with the conventional IBPM and the Crank-Nicolson scheme-based IB method. In conclusion, the proposed approach not only improves the numerical stability, but also increases the computational speed, suitable for solving more realistic problems.