•The validation of a computer simulation code for multiphase flows is implemented.•A fully compressible two-phase homogeneous mixture flow model is presented.•Bubble collapse between two parallel ...walls and saturated film boiling on a sphere are examined.•The predicted time-averaged heat fluxes agree well with those in previous studies.
The present study aims at validating a computer simulation code for compressible interface flows with and without mass transfers. The numerical method was based on a dual-time fully compressible multiphase homogeneous mixture flow model. The interfaces with a large jump in density, pressure, velocity, and temperature were captured using a compressive high-resolution interface-capturing scheme. Lee’s boiling model was adopted for implementing the mass and energy transfers via interfaces. The bubble collapse between two parallel walls was first examined. The bubble profile during the collapse process was predicted and compared with experimental images. The numerical results showed good agreement. To evaluate the present model for multiphase flows, including the effects of heat and mass transfers, computations were performed for saturated film boiling on a sphere at atmospheric pressure. The evolution of the wavy liquid–vapor interface around the sphere during the film boiling process was observed. The time-averaged heat fluxes obtained from the numerical simulation were compared with those predicted from numerical data and analytical correlations. The effects of the superheated wall on heat fluxes were also investigated.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•Fully compressible multiphase model for simulating compressible interfacial flows.•A fully conservative hyperbolic system is solved based on the riemann solver.•Conceptually simple but robust and ...versatile numerical procedure.•Oscillation-free behavior near contact discontinuity.•Multiphase flows with both shock waves and dynamics of interfaces.
We propose a fully compressible multiphase model for simulating compressible interfacial flows. The mathematical model is formulated on the basis of the typical conservation laws for mixtures, including mass, momentum, and energy balance. The mass balance equation in each phase is considered to discretely conserve the mass of each phase; therefore, it is always mass conservative for each phase. The numerical solution procedure for this model is developed using a high-resolution shock-capturing finite-volume method based on the Harten–Lax–van Leer-contact (HLLC) Riemann solver and total variation diminishing (TVD) time-integration schemes for simulating unsteady multiphase flows and capturing strong shocks. The finite-volume Riemann solver is combined with a monotonic upstream-centered scheme for conservation laws (MUSCL) and compressive limiters to maintain a sharp interface. The numerical framework yields a conceptually simple but robust and versatile numerical procedure. Numerical results of benchmark Riemann problems demonstrate the ability of the proposed method to obtain sharp interfaces, free of spurious oscillations, high accuracy, conservation properties, and thermodynamic consistency over various Mach numbers.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•A recently developed two-phase flow model was enhanced and extended for the simulation of ricochet and penetration of water entry bodies.•A coupling algorithm for the fluid-body interaction and ...moving overlapping grid modeling strategy is integrated into the flow solver.•Grid-independent studies of water entry problems of an inclined wedge and two cylinders are addressed.•Investigation of the ricochet of a circular cylinder off the water surface at various initial entry velocities and angles was performed.
In this paper, the enhancement and application of the recently developed two-phase flow model for the simulation of ricochet and penetration of water entry bodies are presented. The simple two-phase three-equation model, which is a reduced version of the full two-fluid model for compressible multiphase flows, is extendedly applied. The numerical procedure is advanced by implementing the scheme on moving overset body-fitted grids to facilitate flow simulation of complex geometries and arbitrary motions of objects and improve computational productivity by employing their flexibility. A coupling algorithm for the fluid-body interaction and a moving overset grid modeling strategy are integrated into the flow solver. Validation with numerical grid refinement and convergence studies of water entry problems is addressed, and the capability and robustness of the present model in the accurate simulation of free surface and water-impact flows are demonstrated. The method was subsequently employed for the investigation of the ricochet of a circular cylinder off the water surface, through which the physical picture of the ricochet is more clearly observed.
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Phytoconstituents presenting in herbal plant broths are the biocompatible, regenerative, and cost-effective sources that can be utilized for green synthesis of silver nanoparticles. Different plant ...extracts can form nanoparticles with specific sizes, shapes, and properties. In the study, we prepared silver nanoparticles (P.uri.AgNPs, P.zey.AgNPs, and S.dul.AgNPs) based on three kinds of leaf extracts (
and
, respectively) and demonstrated the antifungal capacity. The silver nanoparticles were simply formed by adding silver nitrate to leaf extracts without using any reducing agents or stabilizers. Formation and physicochemical properties of these silver nanoparticles were characterized by UV-vis, Fourier transforms infrared spectroscopy, scanning electron microscope, transmission electron microscope, and energy dispersive X-ray spectroscopy. P.uri.AgNPs were 28.3 nm and spherical. P.zey.AgNPs were 26.7 nm with hexagon or triangle morphologies. Spherical S.dul.AgNPs were formed and they were relatively smaller than others. P.uri.AgNPs, P.zey.AgNPs and S.dul.AgNPs exhibited the antifungal ability effective against
and
demonstrating their potentials as fungicides in the biomedical and agricultural applications.
In this study, the complicated behavior of three-dimensional (3D) water entry problems of an oblique cylinder into water is investigated using a free surface model. An efficient free surface solver ...presented in a previous study for modeling ricochet problems (Nguyen et al., 2020b) is extended to the 3D numerical analysis of flow problems in the water entries of solid objects. A numerical scheme is implemented on dynamic overset body-fitted grids to facilitate flow simulations of the complex geometries and arbitrary motions of objects. The numerical method is validated based on studies of grid convergence in water entry problems and via comparisons between the numerical results and experimental data in the literature. The effects of the impact velocity and cylinder-water density ratio on the motion behaviors of the cylinder are investigated. The initial conditions and cylinder density are found to have a remarkable influence on the dynamics of the cylinder, through which the physical context of the problem is more clearly observed.
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•A free surface flow model with a 6-DOF rigid body motion system is briefly introduced.•A grid-convergence study/validation shows good agreement between simulations and experiments.•A numerical study is conducted on a free-falling cylinder at various entry velocities/densities.•The physical behavior of the cylinder's water entry is more clearly observed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•A simple and efficient three-equation two-phase model was transformed to a multi-dimensional general curvilinear coordinate system.•Simulations of 3D complex free surface and water impact flows were ...conducted on curvilinear body-fitted grids.•The CPU cost is significantly reduced by solving the equation system only in the water.•An assessment of accuracy and efficiency of different numerical methods for free surface and water impact flows was performed.
In this work, a simple and efficient three-equation two-phase model is transformed to a multi-dimensional general curvilinear coordinate system for simulation of free surface and water impact flows on curvilinear body-fitted grids. The two-phase model is a reduced version of the Baer–Nunziato model for compressible multiphase flows, in which the governing equations for only the liquid phase are active, whereas those for the air phase are neglected. The CPU cost is significantly reduced by solving the equation system only in the liquid regions, instead of solving the entire computational domain as in classical Euler approaches. The physical system is formulated in a hyperbolic vector form in a curvilinear coordinate system and solved using a monotonic upstream-centered scheme for conservation laws (MUSCL)/Godunov-type finite volume scheme. Compressive MUSCL limiters combined with the high-order finite volume approach result in a sharp interface solution. Validations with numerical grid refinement and convergence studies on dam-break and water impact problems are addressed, and the capability and robustness of the present model for accurate simulation of free surface and water impact flows are demonstrated. The implementation of the present system on a curvilinear body-fitted grid and the use of the Tait equation of state for water for the closure of the compressible system allow the method to solve water impact flow problems with both low-speed and high-speed complex geometries in industry and engineering.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Simultaneous thermodynamic and hydrodynamic mechanisms of underwater explosion phenomenon are investigated numerically.•Both bubble dynamics and temperature fields agree well with experimental data ...and analytical solution.•Thermal boundary layer inside spherical and non-spherical collapsing bubble is analyzed in detail.•An approximate linear relation is proposed to describe relationship between thermal parameters and bubble dynamics.
In this study, we numerically investigate the simultaneous thermodynamic and hydrodynamic mechanisms of underwater explosion (UNDEX). Bubble explosion in water at the collapsing stage is extremely violent and becomes extraordinarily hot, exceeding 1,000 K. The evolution of the bubbles and temperature fields are simulated using a fully compressible mixture model. The deformable bubble and the heat transfer of the internal explosive gas are captured with higher accuracy compared with published data. First, a spherical bubble that collapses and rebounds without the effects of gravity is computed to verify the accuracy of the model. The numerical results in terms of the bubble radius and temperature fields are consistent with analytical solutions based on the Rayleigh–Plesset equation. Next, a real 5.2 g trinitrotoluene UNDEX experimental case is simulated, in which the formation of a non-spherical bubble with a non-symmetric thermal boundary layer is analyzed. An excellent agreement between bubble motions and experimental data is obtained. The temperature inside the collapsing bubble increased significantly, reached a maximum value of approximately 2,000 K at its final stage, and then decreased rapidly. In addition, a spatially non-uniform temperature field and a thicker thermal boundary layer along the jet direction at the collapse stage are observed. Furthermore, a case study is conducted to estimate the bubble dynamics of non-isothermal and isothermal cases. Finally, the effects of the initial equilibrium gas temperature and water temperature on the thermodynamic and hydrodynamic mechanisms of UNDEX are investigated in detail. An approximate non-linear relation is proposed to describe the relationship among the important parameters.
Evolution process of bubble shapes and temperature fields of non-spherical bubble generated by 5.2 g TNT in free-field condition Display omitted
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•To enhance the solution accuracy of the interface computations based on a coupling Level Set (LS) with volume-of-fluid (VOF).•To utilize the advantages of the conservative Level Set method to ...preserve the mass conservation of mixture flow.•Easily implemented based on the free-open source solver (interFoam) of OpenFOAM platform.
Coupling techniques that take advantage of the mass conservation property of the volume-of-fluid (VOF) method and the sharpened interface computation of the Level Set (LS) approach are widely used for computations with high accuracy order demands. In this paper, an enhanced coupling method for interface computations in incompressible two-phase flows is presented. In the proposed method, the solution of the re-initialization LS function is reformulated in a conservative form before it is applied to estimate the interface curvature and interface normal vector. The estimated interface exhibits significant improvements in smoothness and accuracy compared to those obtained with the original VOF method and a previous coupling method. The proposed method is then implemented in an incompressible Navier–Stokes solver (interFoam) in the OpenFOAM platform to solve several benchmark tests. Good agreement between the simulated results and the analytical/benchmark solutions with well-preserved mass conservation is obtained for standard tests, including a reversed single vortex, static droplet, and rising bubble, thus demonstrating the potential of the proposed technique for both academic research and practical applications.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•An accurate shock- and interface-capturing method for simulations of compressible multiphase flows.•A five-equation two-phase model was transformed into a multi-dimensional general curvilinear ...coordinate system.•High-resolution Godunov-type numerical scheme is constructed using a new eigensystem.•Model is validated by compressible multiphase flow problems under the presence of strong shock waves.•Simulations of 3D complex near-field underwater explosions are presented.
In this study, an accurate shock- and interface-capturing method using curvilinear body-fitted structured grids is introduced to simulate compressible multiphase flows with shockwaves. A five-equation model—proficient in capturing unsteady shocks in compressible multiphase flows without nonphysical spurious oscillations—was enhanced by extending it to a multidimensional general curvilinear coordinate system. A new eigensystem was constructed for a monotonic upstream-centered scheme for conservation laws/Godunov-type finite volume scheme that can capture strong shocks in compressible multiphase flows. The developed method was validated using a typical test involving a free-field underwater explosion that produces a strong shockwave in addition to bubble interfaces. Numerical results were compared and found to agree well with the empirical equation and previously published results. Further, the interaction of a shockwave with a wedge was computed to evaluate the shockwave propagation characteristics and appropriate treatment of solid wall boundary conditions. The numerical results show good agreement with the experimental data. Finally, the impact and propagation characteristics of shockwaves in two more complex cases, involving one and two explosions near a rigid cylinder, were numerically analyzed, and the results indicate high impacts of primary blast waves on the structure.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
To examine the transmission dynamics of Mycobacterium tuberculosis (Mtb) isolated from tuberculosis patients in Ho Chi Minh City, Vietnam, we sequenced the whole genomes of 1,635 isolates and ...compared these with 3,144 isolates from elsewhere. The data identify an underlying burden of disease caused by the endemic Mtb lineage 1 associated with the activation of long-term latent infection, and a threefold higher burden associated with the more recently introduced Beijing lineage and lineage 4 Mtb strains. We find that Beijing lineage Mtb is frequently transferred between Vietnam and other countries, and detect higher levels of transmission of Beijing lineage strains within this host population than the endemic lineage 1 Mtb. Screening for parallel evolution of Beijing lineage-associated SNPs in other Mtb lineages as a signal of positive selection, we identify an alteration in the ESX-5 type VII-secreted protein EsxW, which could potentially contribute to the enhanced transmission of Beijing lineage Mtb in Vietnamese and other host populations.
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