Lagrangian Eulerian Framework Research Articles

Fluid-structure interaction induced mixed convection characteristics in a lid-driven square cavity with non-Newtonian power law fluids

The present study aims to numerically explore Fluid-Structure Interaction (FSI) induced mixed convection characteristics in a square cavity filled with a non-Newtonian power-law fluid. The side walls of the cavity under consideration are subjected to constant low temperature having motion in opposite directions while the insulated top wall and the bottom hot wall are kept stationary. A flexible fin is mounted on the bottom wall that essentially serves as a passive flow modulator. To solve the transient flow, thermal, and stress fields, the FSI problem is presented in an arbitrary Lagrangian-Eulerian framework employing the Galerkin finite element method. Different non-Newtonian fluids are represented by the power-law index (n) varied within the range, of 0.6 ≤ n≤ 1.4. Besides, the dynamic as well as mixed convection condition of the flow is analyzed by variation of Reynolds number (100 ≤ Re ≤ 300) and Richardson number (0.1 ≤ Ri ≤ 10.0) respectively. System characteristics have been evaluated in terms of streamline and isotherm contours, spatial and time-averaged Nusselt number as well as Normalized Nusselt number in regard to the “No Fin” case. The outcome of the present study reveals that the efficacy of a flexible fin for a given system depends on both the system dynamic condition (Re) and the mixed convection regime (Ri). The presence of a flexible fin has been found to have positive impact on heat transfer performance for both the shear-thinning and shear-thickening fluids for higher values of Re and Ri. However, for lower values of Re, the inclusion of a flexible fin has been found to adversely affect the heat transfer performance for shear-thickening fluids. Moreover, the thermal field exhibits periodic oscillation properties at Ri = 10, which can be attributed to the induced motion of the flexible fin. This phenomenon has been further elucidated through Power Spectrum Analysis. Results obtained in the present study might provide valuable insights into FSI-induced mixed convection with non-Newtonian fluids having versatile industrial applications such as solar thermal collectors with strategically positioned passive flexible flow modulators.

Nonlinear vibration and acoustic radiation of an internally resonant buckled beam

Although the nonlinear vibration of buckled beam has been thoroughly studied, its acoustic radiation does not get much attention. This paper deals with the nonlinear vibro-acoustic problem of an internally resonant buckled beam immersed in an infinite fluid. A finite element method based on an arbitrary Lagrangian-Eulerian framework is adopted to analyze the nonlinear interaction between the large-deformed buckled beam and the finite-amplitude acoustic waves in the fluid. The effects of acoustic pressure excitation, external harmonic excitation, and internal resonance on the vibro-acoustic responses of the buckled beam are discussed in the first and second primary resonances. It is found that the amplitude of the acoustic pressure can be comparable to the amplitude of the external harmonic force. This leads to an increase in the critical harmonic excitation amplitude for the occurrence of quasi-periodic responses and an increase in the second mode frequency component of quasi-periodic responses compared to the case neglecting the acoustic pressure excitation on the beam. Saturation phenomena are discovered in the second mode frequency components of beam displacement and acoustic pressure. Due to the 2:1 internal resonance, different time-frequency characteristics, quadrupole acoustic directivity patterns with low radiation efficiency, and dipole acoustic directivity patterns with high radiation efficiency can be observed at different harmonic excitation amplitudes and frequencies. Understanding these phenomena will help design loudspeakers and recognize sound sources.

Liquefaction-induced large deformation method with automatic time-step mapping and interfacial interpolation improvement: Case study of the San Fernando dam

This study constructed the u-p equation for saturated soil in the meshfree global weak form within the arbitrary Lagrangian-Eulerian (ALE) framework to solve the problem of liquefaction-induced large deformation induced by strong seismic loading. The interpolation improvement in the near-interface zone was achieved using domain truncation optimization and the local nodal refinement algorithm, and the relative error of the shape function was proposed as the judgment criterion for radial basis function (RBF) field variable mapping. Finally, a high precision meshfree liquefaction-induced large deformation method (MFLLDM) with automatic time step mapping and interfacial zone interpolation improvement was established. The MFLLDM achieved the efficient dynamic updating of soil stress state and pore pressure information in space during the deformation process and more accurately depicted the localized large shear deformation characteristics of the soil in the near-interface zone. The proposed method was integrated into a custom-built large-scale finite element method (FEM) computing system (GEODYNA), based on object-oriented and super element program design technology. This enabled the efficient coupled analysis of MFLLDM in the liquefied-induced large deformation zone and FEM in the small deformation zone. Numerical consolidation examples were used to validate the accuracy, convergence, and applicability of the soil elasto-plastic model for MFLLDM. The method was then used to simulate the liquefaction damage of the San Fernando dam, which reproduced the development process of large slip deformation and high-water pressure ratio for the upstream dam slope.

Spray formation and spray-wall-flow interaction in a gasoline direct-injection (GDI) engine under early-injection conditions: A flow bench study

The work presented in this study aims to understand the spray-wall-flow interaction within a gasoline direct-injection (GDI) engine flow bench under simulated early-injection conditions. The Engine Combustion Network (ECN) Spray G injector is installed in the Darmstadt optically accessible engine flow bench. Under simulated early-injection conditions, the formation of a multi-hole spray and the interaction with characteristic intake flows, such as the intake jet and central tumble flow, are extensively discussed. By reducing the complexity in the number of variables inherent in engine flow and whole-engine simulation, an engine flow bench operating under various mass flow rates is applied in this study. The numerical simulation is carried out using Large Eddy Simulation (LES) under the Eulerian-Lagrangian framework for spray simulation. Experimental data, acquired through particle image velocimetry (PIV) measurements, provides 2-D flow fields on both the central tumble and valve planes, facilitating the validation of in-cylinder flow fields. Furthermore, experimental data obtained through Mie scattering is utilized to investigate spray formation and evolution within the GDI engine, providing the liquid penetration length and liquid spray angle. Comparison between the numerical and experimental data demonstrates several agreements. Moreover, the variation of different spray plumes under different mass flow rates is observed in the case of both experimental and numerical data. Increasing the mass flow rate distorts the overall plume shape and shifts it away from the intake port. This phenomenon is examined by extracting the liquid volume fraction and vapor fields of each plume. Spray plumes encounter different convective disturbances and evaporation due to their local characteristic in-cylinder flow. Furthermore, spray-wall-flow interaction and wall film deposits are observed during the injection. Lastly, the influence of the spray-induced turbulence is analyzed under different mass flow rates.

Validation of a Eulerian–Lagrangian numerical algorithm for simulating ultra-coarse particles transported in horizontal and vertical hydraulic pipes

Investigation on the characteristics of coarse and ultra-coarse particles transported in hydraulic conveying pipe is essential to design hydraulic conveying system with high efficiency and reliability. However, the modeling of the particles with a finite size larger than the mesh for fluid discretization is intractable, because the unresolved point-particle methods are difficult to converge in the calculation and the particle-resolved methods cannot afford the computational cost for engineering problem. A numerical algorithm based on the Eulerian–Lagrangian framework is developed to simulate such two-phase flows. The solvers of the computational fluid dynamics (CFD) and the discrete element method (DEM) are coupled through an in-house developed interface code. In the code, a diffusion-based averaging method is employed to smooth the contributions of large particle in the particle volume fraction, the interphase forces and the interactions between turbulence and particles. The interpolation of fluid velocity is also improved so that the calculations of the interphase forces are more accurate. The authenticity of the numerical algorithm is validated against available experimental results. The validating scenarios are the millimeter- and centimeter-sized particles conveyed in both horizontal and vertical pipes under various conveying speeds and particle concentrations. The results show the numerical algorithm can simulate large particles in the fine CFD meshes. More importantly, some distinct features in the particle distribution and the characteristics of turbulence in the experiments are well reproduced by the simulations.

Droplet evaporation on curved surfaces: transients of internal and external transport phenomena

We explore the transient evolution of thermo-fluid-dynamics of evaporating sessile droplets over curved substrates in the liquid and gaseous domains. A computational model using the Arbitrary Lagrangian-Eulerian framework is adopted. The governing equations in both liquid and gaseous domains are solved in a fully coupled manner, considering coupled effects of evaporative cooling and heat advection due to bulk fluid motion. This bulk motion in the liquid domain is caused by natural advection due to thermal actuations such as thermal Marangoni flow and buoyancy-driven convection. For the gaseous domain, the additional effects of solutal convection (due to vapour-concentration variation), Stefan flow and interfacial viscous stresses are also considered. To depict a generalized role of substrate curvature, both concave and convex surfaces with curvatures over a wide range are studied. The surface wettability effects are also explored by varying the true contact angle of the droplets. Computational predictions on evaporation rate and internal flow field are validated against experimental results from literature. The interplay of wetting state and substrate curvature is noted to substantially affect the evaporation process and its thermo-fluidics. The convex curvature significantly augments internal advection while the same is weakened over concave substrates due to altered mass loss rate. Consequently, the duration of multi-vortex Marangoni flows in the development stages of evaporation and the advection in the external gaseous domain is markedly different for different curvatures. Further, on superhydrophobic curved surfaces, the effects of re-distributed evaporative fluxes play a major role. In such cases, the reduced mass flux over a large interfacial area near the periphery expedites the stable state Marangoni and external flow features.

An investigation on pyrolysis characteristics of low-sulfur heavy fuel oil spray under diesel engine-like conditions

The pyrolysis characteristics of low-sulfur heavy oil fuel (HFO) spray under diesel engine-like conditions were investigated for the first time using both experimental and numerical methods. The high speed diffused back-imaging method was adopted to measure the macroscopic features of the low-sulfur HFO spray, and its products were sampled and analyzed by the gas chromatography with mass spectrometry. The low-sulfur HFO spray behaves as a quasi-evaporating spray under high temperature conditions, integrating the characteristics of evaporating and non-evaporating sprays. The increase of temperature shows little effect on its penetration characteristics, but a great effect on the vapor distribution. The low-sulfur HFO spray can pyrolyze at the temperature below 650 K due to the high heating-up rate and ambient pressure, and the aromatics contained in it are easy to pyrolyze, producing some oxygenate and amide components. Based on the experimental results, an integral pyrolysis model with multi-component evaporation and pyrolysis was established and implemented into the Eulerian-Lagrangian framework to simulate the low-sulfur HFO spray, and its predictions agree very well with the experimental results. The pyrolysis shows a large effect on the HFO spray evolutions. Ignoring the pyrolysis process would underestimate the droplet temperature and distribution number at the HFO spray tip and overestimate the vapor concentration of heavy-end hydrocarbons, because most of them are trapped inside the droplet enclosed by the pyrolytic residues.

External Stefan and Internal Marangoni Thermo-Fluid Dynamics for Evaporating Capillary Bridges.

We probe the evaporation mechanisms of wettability-moderated, confined capillary bridges and bulges. For the first time, we explore the internal Marangoni hydrodynamics and external Stefan advection dynamics in the surrounding gaseous domain due to evaporative effects. A transient simulation approach based on the level set (LS) method and the Arbitrary Lagrangian-Eulerian (ALE) framework was adopted to computationally model the capillary bridge profiles and evaporation phenomenon with generic contact line dynamics (both CCR and CCA modes). The governing equations corresponding to the transport processes in both the liquid and gaseous domains are simulated in a fully coupled manner with appropriate boundary conditions to precisely trace the liquid-vapor interface and the three-phase contact point during evaporation. The effect of the bridge confinement phenomenon, i.e., the extent of confined ambient surrounding the liquid-vapor interface between the solid surfaces, is explored. Also, the role of wetting state and contact line dynamics during CCR and CCA modes of evaporation were probed, and good agreement with experimental observations was noted. Results show that the evaporation rate is primarily dictated by the confinement phenomenon, and wettability effects play a marginal role. A higher confinement curtails the evaporation rate due to an increased local vapor concentration around the liquid bridges. However, the wetting state substantially affects the internal Marangoni effect dynamics and the Stefan advection dynamics due to its explicit influence on the nonuniform evaporative flux along the liquid-vapor interface. Between superhydrophobic confinements, the contact lines are confined in the wedge-shaped region, thereby locally augmenting the vapor concentration. As a result, the large evaporative flux near the bulge region develops a higher temperature gradient, thereby inducing upscaled thermal Marangoni flow compared to hydrophilic confinements. These findings may have significant implications for the efficient designing and development of thermofluidic systems involving thermal transport, mixing, and deposition of dissolved particles in liquid bridges.

The Impact of Flapping Trajectories on the Induced Thrust of a Single and Tandem Configuration Flapping Foil

Abstract The development of propulsion devices by using the propulsive mechanisms of aquatic animals such as fish is a challenging task. An attempt has been made to replicate the fishtailed motion that caused thrust in the current investigation. At a low Reynolds number of Re = 1173, the propulsive performance of National Advisory Committee for Aeronautics 0012 flapping foils enduring distinct flapping trajectories (fishtailed and elliptical) is evaluated. A dynamic mesh arbitrary Lagrangian–Eulerian framework is used to understand the desired flapping motion of the foils while solving the flow via incompressible Navier–Stokes equations. Along with the flapping trajectory, the effects of the Strouhal number (St), inter-foils distance (Lx), and phase angle (φ) between the foils on the produced thrust are examined. The results demonstrate that using tandem configuration flapping foil with elliptical and fishtailed flapping can significantly increase the induced thrust and propulsive efficiency.

A hybrid multi-scale/finite element method in arbitrary Lagrangian-Eulerian framework for predicting nonlinear structural-acoustic responses of a large-deformable beam in fluid

This paper introduces a novel hybrid multi-scale/arbitrary Lagrangian-Eulerian finite element method (HMS/ALE-FEM) for addressing the nonlinear vibro-acoustic problem of a large-deformed beam in an infinite fluid. In the HMS/ALE-FEM, the vibrational response of the beam is tackled through modal superposition and a temporal multi-scale approach, while the acoustic wave emitted from the beam is addressed using the arbitrary Lagrangian-Eulerian finite element method (ALE-FEM). An alternating frequency/time domain technique is employed to handle the displacement and velocity of the moving mesh and the acoustic pressure on the beam surface. To validate the HMS/ALE-FEM, it is compared against the finite element method for beam response and the ALE-FEM for acoustic response, serving as a reference method. Taking the nonlinear vibro-acoustic problem of a buckled beam with 2:1 internal resonance as an example, the results of the HMS/ALE-FEM are compared with those of the reference method. The results show that the HMS/ALE-FEM is in good agreement with the reference method under different harmonic excitation amplitudes and frequencies. Due to the 2:1 internal resonance, double modes can be generated, and the second mode amplitudes of both beam displacement and acoustic pressure remain constant as the excitation amplitude varies. Notably, the HMS/ALE-FEM provides direct access to mode amplitude and phase information for beam displacement and acoustic pressure on the beam surface, offering valuable insights into fluid-structure interaction mechanisms in both single- and double-mode scenarios.

Numerical Study of the Effect of Primary Nozzle Geometry on Supersonic Gas-Solid Jet of Bypass Injected Dry Powder Fire Extinguishing Device

A two-way coupled model between polydisperse particle phases with compressible gases and a density-based coupling implicit solution method, combining the third-order MUSCL with QUICK spatial discretization scheme and the second-order temporal discretization scheme, are constructed based on the discrete-phase model (DPM) and the stochastic wander model (DRWM) in the Eulerian–Lagrangian framework in conjunction with a unitary particulate source (PSIC) approach and the SST k-ω turbulence model. The accuracy of the numerical prediction method is verified using previous supersonic nozzle gas-solid two-phase flow experiments. Numerical simulation of a two-phase jet of dry powder extinguishing agent gas with pilot-type supersonic nozzle was performed to analyze the influence of geometrical parameters, such as the length ratio rL and the area ratio rA of the main nozzle on the two-phase flow field, as well as on the jet performance indexes, such as the particle mean velocity vp,a, velocity inhomogeneity Φvp, particle dispersion Ψp, particle mean acceleration ap,a, etc. By analyzing the parameters, we indicate the requirements for the combination of jet performance metrics for different flame types such as penetrating, spreading, and dispersing.

Nonlinear supersonic flutter of a composite panel backed by an acoustic cavity with finite-amplitude sound waves

In this paper, an implicit partitioned fluid-structure-acoustic interaction method is presented for predicting nonlinear aeroelastic response of an elastic composite laminated panel backed by an acoustic cavity and subject to a supersonic flow. The method is formulated in an arbitrary Lagrangian-Eulerian framework based on the unsteady Navier-Stokes equations for the supersonic flow, a geometrical nonlinear dynamics model for the composite laminated panel, and the nonlinear Westervelt equation for the finite-amplitude sound waves in cavity. A theoretical fluid-structure-acoustic model of the supersonic panel is proposed for validating the present numerical method, in which the nonlinear structural model of the panel, the first-order piston aerodynamics model of the supersonic flow and the nonlinear sound wave model of the cavity are coupled in a monolithic manner. It is found that cavity acoustic resonance can appear in the case a vibration mode of the panel coalescing with an acoustic mode of the cavity. Several new physical features of nonlinear acoustic resonance have been discovered, such as the presence of shock wave with high pressure gradients travelling along the resonant cavity in axial direction and the presence of higher-order harmonic wave components, which emphasize a nonlinear acoustic wave model of the cavity must be used to fully characterize these phenomena. In addition, the nonlinearity of the standing wave is quantitatively related to the acoustic modes by means of a proper orthogonal decomposition analysis.

A yarn-scale woven fabric model including significant slippage formulated within the Arbitrary Lagrangian Eulerian framework

A numerical model is proposed to simulate significant yarn slippage and unweaving in woven fabrics using the Arbitrary Lagrangian Eulerian (ALE) method. Woven fabrics were modeled at the yarn scale using 1D ALE elements with additional slip displacement degrees of freedom (DOF). The relatively weak bending stiffness of the yarn was included using a rotation-free approach. A weave kinematic constraint between crossing yarns allowed an efficient description of the deformation modes due to the yarn assembly such as in-plane shear. In particular, normal compaction at weave points was taken into account using an additional crimp amplitude DOF and couplings of the fabric’s cohesion with the normal and lateral compaction were considered. To deal with yarn unweaving, a specific void-ALE 1D element was developed in order to avoid remeshing, time-step reduction (explicit scheme) and early deactivation of the weave kinematic constraint. To demonstrate the capabilities of this numerical model, common characterization tests such as in-plane and out-of-plane pullouts, which induced unweaving were simulated. Finally, a first forming simulation on a hemisphere was performed to verify whether the cohesion of the fabric remained well represented in situations without loss of cohesion before simulating forming on a prismatic punch involving significant yarn slippage.

Drag, lift and torque correlations for axi-symmetric rod-like non-spherical particles in locally linear shear flows

This paper derives new correlations to predict the drag, lift and torque coefficients of axi-symmetric non-spherical rod-like particles for several fluid flow regimes and velocity profiles. The fluid velocity profiles considered are locally uniform flow and locally linear shear flow. The novel correlations for the drag, lift and torque coefficients depend on the particle Reynolds number Rep, the orientation of the particle with respect to the main fluid direction θ, the aspect ratio of the rod-like particle α, and the dimensionless local shear rate G̃. The effect of the linear shear flow on the hydrodynamic forces is modeled as an additional component for the resultant of forces acting on a particle in a locally uniform flow, hence the independent expressions for the drag, lift and torque coefficients of axi-symmetric particles in a locally uniform flow are also provided in this work. The data provided to fit the coefficient in the new correlation are generated using available analytical expressions in the viscous regime, and performing direct numerical simulations (DNS) of the flow past the axi-symmetric particles at finite particle Reynolds number. The DNS are performed using the direct-forcing immersed boundary method. The coefficients in the proposed drag, lift and torque correlations are determined with a high degree of accuracy, where the mean error in the prediction lies below 2% for the locally uniform flow correlations, and bwlow 1.67%, 5.35%, 6.78% for the correlation accounting for the change in the drag, lift, and torque coefficients in case of a linear shear flow, respectively. The proposed correlations for the drag, lift and torque coefficients can be used in large-scale simulations performed in the Eulerian-Lagrangian framework with locally uniform and non-uniform flows.

CFD study of gas-powder injection characteristics in a novel lance with supersonic shrouding jet

Supersonic gas–solid jets are widely applied in the spraying coating processes, drug delivery, and metallurgical reactors, due to exceptional penetrating capabilities. In this study, a novel lance is designed to increase the penetration depth of gas–solid flow by utilizing a supersonic shrouding jet (SSJ). Subsequently, the numerical model based on the Eulerian-Lagrangian framework is applied to analyze the supersonic gas-powder flow within the lance. After validating the reliability of numerical model with experimental data, the gas-powder flow characteristics are discussed. The results indicate that the presence of SSJ enhances the powder velocity and penetration depth significantly by blending supersonic gas. Moreover, the particle-gas momentum interaction primarily occurs inside the central pipe and downstream of the lance exit. Along the radial direction, the particle dispersion is the result of the combined interplay between lift force and particle–particle collisions. The lift force enhances particle collision frequency, and these collisions, in turn, facilitate the conversion of axial momentum into radial momentum, resulting in substantial radial acceleration. When SSJ exits, the particle radial dispersion is constrained, primarily due to the reduced particle residence time. Additionally, the introduction of low-temperature oxygen from SSJ results in a reduction in both the carrier gas and particle temperatures. The results provide meaningful insights into understanding the supersonic gas–solid flow mechanisms of the SSJ lance.

Arbitrary Lagrangian-Eulerian finite element approximations for axisymmetric two-phase flow

We analyze numerical approximations for axisymmetric two-phase flow in the arbitrary Lagrangian-Eulerian (ALE) framework. We consider a parametric formulation for the evolving fluid interface in terms of a one-dimensional generating curve. For the two-phase Navier-Stokes equations, we introduce both conservative and nonconservative ALE weak formulations in the 2d meridian half-plane. Piecewise linear parametric elements are employed for discretizing the moving interface, which is then coupled to a moving finite element approximation of the bulk equations. This leads to a variety of ALE methods, which enjoy either an equidistribution property or unconditional stability. Furthermore, we adapt these introduced methods with the help of suitable time-weighted discrete normals, so that the volume of the two phases is exactly preserved on the discrete level. Numerical results for rising bubbles and oscillating droplets are presented to show the efficiency and accuracy of these introduced methods.

Lifex-cfd: An open-source computational fluid dynamics solver for cardiovascular applications

Computational fluid dynamics (CFD) is an important tool for the simulation of the cardiovascular function and dysfunction. Due to the complexity of the anatomy, the transitional regime of blood flow in the heart, and the strong mutual influence between the flow and the physical processes involved in the heart function, the development of accurate and efficient CFD solvers for cardiovascular flows is still a challenging task. In this paper we present life▪-cfd, an open-source CFD solver for cardiovascular simulations based on the life▪ finite element library, written in modern C++ and exploiting distributed memory parallelism. We model blood flow in both physiological and pathological conditions via the incompressible Navier-Stokes equations, accounting for moving cardiac valves, moving domains, and transition-to-turbulence regimes. In this paper, we provide an overview of the underlying mathematical formulation, numerical discretization, implementation details and examples on how to use life▪-cfd. We verify the code through rigorous convergence analyses, and we show its almost ideal parallel speedup. We demonstrate the accuracy and reliability of the numerical methods implemented through a series of idealized and patient-specific vascular and cardiac simulations, in different physiological flow regimes. The life▪-cfd source code is available under the LGPLv3 license, to ensure its accessibility and transparency to the scientific community, and to facilitate collaboration and further developments. Program summaryProgram Title:life▪-cfdCPC Library link to program files:https://doi.org/10.17632/hzsnc3jgds.1Developer's repository link:https://gitlab.com/lifex/lifex-cfdLicensing provisions:LGPLv3Programming language: C++ (standard ≥17)Supplementary material:https://doi.org/10.5281/zenodo.7852088 contains the application executable in binary form, compatible with any recent enough x86-64 Linux system, assuming that glibc version ≥ 2.28 is installed. Data and parameter files necessary to replicate the test cases described in this manuscript are also available.Nature of problem: The program allows to run computational fluid dynamics simulations of cardiovascular blood flows in physiological and pathological conditions, modeled through incompressible Navier-Stokes equations, including moving cardiac valves, moving domains (such as contracting cardiac chambers) in the arbitrary Lagrangian-Eulerian framework, and transition-to-turbulence flow. Given the scale of the typical applications, the program is designed for parallel execution.Solution method: The equations are discretized using the Finite Element method, on either tetrahedral or hexahedral meshes. The software builds on top of deal.II, implementing the mathematical models and numerical methods specific for CFD cardiovascular simulations. Parallel execution exploits the MPI paradigm. The software supports both Trilinos and PETSc as linear algebra backends.Additional comments including restrictions and unusual features: The program provides a general-purpose executable that can be used to run CFD simulations without having to access or modify the source code. The program allows to setup simulations through a user-friendly yet flexible interface, by means of readable and self-documenting parameter files. On top of that, more advanced users can modify the source code to implement more sophisticated test cases. life▪-cfd supports checkpointing, i.e. simulations can be stopped and restarted at a later time.

Supersonic dusty gas flow past a cylinder in Eulerian–Lagrangian framework

The present study utilizes computational methods to analyze two-dimensional particle-laden flow over a circular cylinder. The effect of seeding of dust particles in the viscous flow of a compressible gas is analyzed. A new solver has been developed for the purpose of studying multi-phase flows in the supersonic regime. Most of the prior research has primarily focused on flows characterized by low Mach numbers and the absence of shock waves, and there have been very few studies dealing with supersonic dusty gas flows. This study considers a supersonic Mach number and investigates the effect of particle size and particle volume fraction on dusty-gas flow over a circular cylinder. The simulation results reveal that the seeding of particles in the flow creates perturbations. The present work also highlights the influence of particles on flow separation and the subsequent increase in the skin friction coefficient and coefficient of drag. The study shows that for supersonic flows, at the same volume fraction, larger particle size creates more instabilities in the flow, while smaller particles are responsible for increased drag on the cylinder, owing to a greater frequency of collisions.

A conservative sharp interface method for two-dimensional incompressible two-phase flows with phase change

A conservative sharp interface method is proposed in this work to simulate two-dimensional/axisymmetric incompressible two-phase flows with phase change. In this method, we use the cut cell method to generate unstructured meshes near the interface, of which the cell edges overlap with the interface at each time step. On such mesh, the mass and heat transfer during phase change and all the jump conditions can be incorporated into the calculation of fluxes at the cell edges, to ensure that they are strictly satisfied at the interface in a sharp manner. The governing equations, including the incompressible Navier–Stokes equations, heat equation, and vapor mass fraction equation, are discretized by a second-order finite volume method in the arbitrary Lagrangian–Eulerian framework. To well couple the mass, heat, momentum, and interface evolution, the solution procedure is carefully designed and performed with several techniques. In such a way, the sharp discontinuity of the velocity, stress, temperature gradient, and vapor fraction, caused by the mass/heat transfer during phase change, can be simulated accurately and robustly. The performance of this method is systematically examined by cases of phase change at or below the saturated temperature, including vapor bubble in superheated liquid, film boiling, droplet evaporation at different relative humidity conditions, droplet evaporation under gravity, and droplet evaporation under forced convection. The applicability of the present method for incompressible two-phase flows with phase change is well demonstrated by comparing the numerical results with the benchmark, theoretical or experimental ones.

Phase change and combustion of iron particles in premixed CH[formula omitted]/O[formula omitted]/N[formula omitted] flames

Metal powder is a promising carbon-free and recyclable energy carrier. Direct combustion of the micron-sized iron particles involves complex physical and chemical processes, such as heat transfer, surface reaction, and phase change. In this work, computational modelling of these processes is investigated and validated against experiments. A single iron particle combustion and phase change model is proposed in an Eulerian–Lagrangian framework. The new phenomenological model considers five stages, i.e., solid phase oxidation, melting of iron oxides and raw iron, liquid phase oxidation, cooling of liquid iron oxides, and solidification of super-cooled liquid iron oxides. The proposed model is first validated and then adopted in simulations of micron-sized iron particle combustion in premixed CH4/O2/N2 flames to study the effects of ambient temperature and oxygen concentration on single iron combustion. Results show that the new model is capable of replicating the melting, heterogeneous surface reaction, cooling, and solidification processes. Two-stage solidification is observed in experiments and modelled in simulations. This two-stage solidification includes a fast solidification with a significant temperature rise (∼150–200 K) and a thermal equilibrium solidification featuring a constant temperature and a slight particle radiant intensity decrease. In addition, a diffusion-controlled mechanism is identified during the melting process, in which the oxygen concentration dominates the melting time and the subsequent burning time. Furthermore, it is found that the reaction between iron and CH4/O2/N2 flame products, such as CO2 and H2O, plays a non-negligible role in the iron combustion process.