Two-phase Flow Model Research Articles

Numerical Simulation and Optimization Study on the Flow Field Characteristics of a Double-Slot Spillway

To investigate the flow characteristics of a novel dual-slot overflow channel, a research approach integrating physical experiments and numerical simulations was adopted. A three-dimensional model of the overflow channel was developed, employing the RNG k-ε turbulence model and the VOF two-phase flow model to optimize the numerical simulation of the high-low dual-slot flow field. Physical experiments were conducted to verify and analyze the hydraulic characteristics of the high-low overflow channel, including the longitudinal water surface profile and flow patterns. The numerical simulation results aligned well with the physical model test results. By analyzing the flow field of the dual-slot counterflow spillway, the flow characteristics at both the spillway and outlet sections were identified. This study focused on the water surface profile along the spillway, the pressure distribution, and the counterflow characteristics of the protruding water tongue, and explored optimization strategies for the WES surface and spillway design. Physical model tests were conducted on the final optimized design, yielding good agreement between the theoretical predictions and experimental results, thereby confirming the feasibility of the energy dissipation methods for both high and low spillways. The research outcomes offer valuable references for related engineering applications.

Computer Simulation and Speedup of Solving Heat Transfer Problems of Heating and Melting Metal Particles with Laser Radiation

The study of the process of laser action on powder materials requires the construction of mathematical models of the interaction of laser radiation with powder particles that take into account the features of energy supply and are applicable in a wide range of beam parameters and properties of the particle material. A model of the interaction of pulsed or pulse-periodic laser radiation with a spherical metal particle is developed. To find the temperature distribution in the particle volume, the non-stationary three-dimensional heat conductivity equation with a source term that takes into account the action of laser radiation is solved. In the plane normal to the direction of propagation of laser radiation, the change in the radiation intensity obeys the Gaussian law. It is possible to take into account changes in the intensity of laser radiation in space due to its absorption by the environment. To accelerate numerical calculations, a computational algorithm is used based on the use of vectorized data structures and parallel implementation of operations on general-purpose graphics accelerators. The features of the software implementation of the method for solving a system of difference equations that arises as a result of finite-volume discretization of the heat conductivity equation with implicit scheme by the iterative method are presented. The model developed describes the heating and melting of a spherical metal particle exposed by multi-pulsed laser radiation. The implementation of the computational algorithm developed is based on the use of vectorized data structures and GPU resources. The model and calculation results are of interest for constructing a two-phase flow model describing the interaction of test particles with laser radiation on the scale of the entire calculation domain. Such a model is implemented using a discrete-trajectory approach to modeling the motion and heat exchange of a dispersed admixture.

An Application of Upwind Difference Scheme with Preconditioned Numerical Fluxes to Gas-Liquid Two-Phase Flows

A time-consistent upwind difference scheme with a preconditioned numerical flux for unsteady gas-liquid multiphase flows is presented and applied to the analysis of cavitating flows. The fundamental equations were formulated in general curvilinear coordinates to apply to diverse flow fields. The preconditioning technique was applied specifically to the numerical dissipation terms in the upwinding process without changing the time derivative terms to maintain time consistency. This approach enhances numerical stability in unsteady multiphase flow computations, consistently delivering time-accurate solutions compared to conventional preconditioning methods. A homogeneous gas-liquid two-phase flow model, third-order Runge-Kutta method, and the flux difference splitting upwind scheme coupled with a third-order MUSCL TVD scheme were employed. Numerical tests of two-dimensional gas-liquid single- and two-phase flows over backward-facing step with different step height and flow conditions successfully demonstrated the capability of the present scheme. The calculations remained stable even for flows with a very low Mach number of 0.001, typically considered incompressible flows, and the results were in good agreement with the experimental data. In addition, we analyzed unsteady cavitating flows at high Reynolds numbers and confirmed the effectiveness and applicability of the present scheme for calculating unsteady gas-liquid two-phase flows.

Reviewing two-phase flow modeling in membrane processes through computational fluid dynamics

Reviewing two-phase flow modeling in membrane processes through computational fluid dynamics

Small-scale interface dynamic modelling based on the geometric method of moments for a two-scale two-phase flow model with a disperse small scale

In this contribution, we develop a versatile formalism to derive unified two-phase models describing both the separated and disperse regimes as introduced by Loison et al. (Intl J. Multiphase Flow, vol. 177, 2024, 104857). It relies on the stationary action principle and interface geometric variables. This contribution provides a novel method to derive small-scale models for the dynamics of the interface geometry. They are introduced here on a simplified case where all the scales and phases have the same velocity and that does not take into account large-scale capillary forces. The derivation tools yield a proper mathematical framework through hyperbolicity and signed entropy evolution. The formalism encompasses a hierarchy of small-scale reduced-order models based on a statistical description at a mesoscopic kinetic level and is naturally able to include the description of a disperse phase with polydispersity in size. This hierarchy includes both a cloud of spherical droplets and non-spherical droplets experiencing a dynamical behaviour through incompressible oscillations. The associated small-scale variables are moments of a number density function resulting from the geometric method of moments (GeoMOM). This method selects moments as small-scale geometric variables compatible with the structure and dynamics of the interface; they are defined independently of the flow topology and, therefore, this model allows the coupling of the two-scale flow with an inter-scale transfer. It is shown, in particular, that the resulting dynamics provides partial closures for the interface area density equation obtained from the averaging approach.

Effect of Blade Number on Internal Flow and Performance Characteristics in Low-Head Cross-Flow Turbines

Cross-flow turbines are widely used in microhydropower systems because of their cost-effectiveness, environmental sustainability, adaptability, and robust design. However, their relatively lower efficiency than other turbine types limit their application in large-scale projects. Previous studies have identified poor flow profiles as a significant factor contributing to inefficiency, with the number of blades playing a critical role in the flow behavior, efficiency, and structural stability. This study employed numerical simulations to analyze how varying the number of blades affects the internal flow characteristics and performance of the turbine at, and off, its best operating points. Configurations with 16, 20, 24, 28, 32, 36, 40, and 44 blades were investigated under constant low-head conditions, fully open valve settings, and varying runner speeds. Simulations were performed using ANSYS CFX, incorporating steady-state conditions, a two-phase flow model with a movable free surface, and a shear stress turbulence model. The results indicate that the 28-blade configuration achieved a maximum hydraulic efficiency of 83%, outperforming the preset 24-blade setup by 6%. Flow profiles were examined using pressure and velocity gradients to identify regions of adverse pressure. Due to the impulse nature of the turbine, the flow profile is more sensitive to changes in the flow speed than to pressure. The flow trajectory showed stability in the first stage but exhibited discrepancies in the second stage, which were attributed to turbulence, recirculation, and shaft flow impingement. The observed performance improvements were linked to reduced hydraulic losses due to flow separation and friction, emphasizing the significance of the number of blades and the regions of optimal efficiency under low-head conditions.

Two-phase reactive transport modeling of heterogeneous gas production in a low- and intermediate-level radioactive waste repository

Deep geological disposal is a widely proposed approach for safe storage of low- and intermediate-level radioactive waste (L/ILW) for tens to hundreds of thousands of years. Although the use of cement materials will maintain a high pH environment that is favorable for radionuclide retention, slows down metal corrosion, and suppresses microbial activity, different gases may still be produced by chemical reactions, such as pH-dependent anoxic corrosion of metals, and the degradation of organic matter as well. Both reactions consume water and may lead to the formation of a free gas phase within and around the repository.In order to investigate the controlling factors of this gas production processes, a coupled reactive transport model of component-based two-phase flow in the OpenGeoSys framework is adopted here. Building on the previous work by Huang et al. (2021), this work extends the geometric configuration of the model from a single drum to the scale of a waste container (12 drums) in order to more realistically model the water and gas fluxes. The geochemical evolution of a container filled with cemented steel drums and surrounded by mortar and host rock is simulated in a two-dimensional setup over 500 years. The relative humidity in the pore space as measure of water availability determines the chemical reactivity.We have conducted a sensitivity study for the influence of mortar capillarity and permeability on gas production over time in the waste drums. As expected, the amount of gas produced within the first several years depends primarily on the initial water content within the waste drum and the amount of fast degradable waste stored in a drum. Later, this feedback system is forced into a new equilibrium, where the water transport has to match the water consumption rate at the waste package. Both, the mortar capillarity and permeability control the point in time when the equilibrium is reached and the subsequent rate of gas production.This study shows how reactive transport models are capable to help with the understanding of couplings between chemical and transport processes that control gas generation in L/ILW waste repositories, especially in barrier systems with different material properties. Future studies could benefit from more accurate parameterization of the chemical reactions, depending on the availability of new experimental data and/or more realistic process-based model approaches.

The droplet dynamics of asymmetrical impingement on moving ridged surface.

The depth of research into the mechanism of droplet impacting structured surfaces dictates the efficacy of their applications. The impact stress generated when a droplet impacts a surface is a pivotal factor influencing the efficiency of surface applications, ultimately determining the extent of surface wear. Despite the systematic examination of impact force, there remains a scarcity of research on impact stress and its mitigation strategies. Consequently, the objective of this study is to delve into the mechanisms that reduce maximum impact stress following the introduction of aerodynamic boundary layer and structural design. Based on experimental investigations, we examined the dynamic behavior of droplet impacting moving ridged surface with varying offset ratios across different tangential and normal Weber numbers. This study emphasizes the impact behavior phase diagram, droplet spreading length, and other relevant parameters. Furthermore, we systematically analyzed the evolution of the flow field and surface stress during the impact process benefit from a numerical simulation of a two-phase laminar flow model. This study shows that the impact of droplets on moving ridged surfaces significantly influences stress reduction, with a focus on asymmetric droplet impacts. The research establishes a phase diagram for droplet impact behaviors across varying tangential Weber number (Weτ), normal Weber number (Wen) and offset ratio (χ), and some unified models about the maximum spreading diameter (Dmax) of the droplet are obtained based on the above variables. Besides, a model based on Prandtl's boundary layer theory emphasizes and proves the positive effect of the introduction of air layer on the reduction of maximum impact stress. Notably, the offset ratio significantly influences stress distribution, the maximum impact stress shows a non-monotonic change from increasing first to decreasing as χ increases considering the rotation of droplet. This research contributes valuable insights into surface design strategy for enhancing the resistance to droplet impact wear. These findings have broad implications for industrial applications where managing droplet impingement is crucial.

A heat transfer model for two-phase flow in an ejector refrigeration system

A heat transfer model for two-phase flow in an ejector refrigeration system

Effects of gravity on the cell performance of proton exchange membrane water electrolyzer

Hydrogen is of great significance for building a low-carbon and safe energy system. The proton exchange membrane water electrolyzer (PEMWE) is considered a highly promising hydrogen production device. However, due to the complex physical and chemical processes within the cell, and the impact of gravity effect on the cell characteristic is unclear. Analyzing the impact of gravity on cell performance is critical. In this study, the three-dimensional two-phase flow models are developed for the PEMWE, the models couple many physical fields, including the hydrodynamics, electrochemical reaction kinetics, mass transfer, heat transfer, two-phase flow based on Euler model, and gravity effect. The simulation model is verified through experiment results. The effect of gravity on the cell performance is investigated, the influences of gravity under different placement directions are compared, and the impact of the cell voltage on the transport characteristics is discussed under the gravity effect. Results show that the gas transport and heat transfer are enhanced under the gravity, the active sites in the catalytic layer can be timely released due to the accelerated bubble removal, the polarization performance is accordingly improved. The cell performance with the gravity effect under vertical placement is higher than that with the gravity effect under horizontal placement because of the improved mass transfer, but the mixture velocity at anode flow channel is decreased. Moreover, as the cell voltage increases, the electrochemical reaction rate is enhanced, the heat transfer is increased, and the volume fraction of disperse phase in anode flow channel is accordingly increased. This study provides a theoretical reference for further investigating transport characteristics and optimising the cell performance.

SIMULATION AND EXPERIMENT ON PET AND BOPP MIXTURE SEPARATION BASED ON EDEM–FLUENT

To improve the efficiency and quality of polyethylene terephthalate (PET) recycling, the air separation recovery of PET and biaxially oriented polypropylene (BOPP) materials in broken plastic beverage bottles was explored and analyzed in this study. A gas–solid two-phase flow model was established to simulate the movement of flaky mixtures with different textures in the wind field. Analysis results show that wind velocity at the air outlet (A), initial material falling speed (B), angle between wind velocity at the outlet (C) and the horizontal direction, and material feed rate (D) are the key parameters that affected the separation. On the basis of the simulation results, an orthogonal experiment with four factors and three levels was designed, and range analysis and ANOVA were performed on the test results, which present the result of the influencing degree of each factor on the separation rate as follows: A > B > C > D. The fitting analysis of 3D scattered-point surfaces, the interaction between A and B exerts the greatest influence on the separation rate in the six groups of interaction experiments. The best separation parameters are acquired for the experiment, and the mass percentage of recycled PET is 99.96%, which achieve recycling requirements. Keywords: EDEM–Fluent coupling; Air separation; Orthogonal experiment; PET/BOPP mixture

A Data Assimilation-Based Method for Real-Time Monitoring and Estimation of Gas Influx Size and Distribution During Gas Migration in a Marine Drilling Riser

Effective well control is essential in marine drilling operations to prevent catastrophic blowouts that endanger human lives and cause severe environmental damage, including long-lasting impacts on marine ecosystems. Accurate real-time monitoring and management of well conditions after taking gas influxes are critical for maintaining safety and environmental protection during offshore drilling operations.When a gas influx becomes trapped in a closed marine drilling riser, its upward migration can result in excessively high surface pressure, presenting significant risks to offshore drilling and well control. Therefore, the accurate estimation of downhole gas influx size and distribution during gas migration events is crucial for effectively managing these situations. The complexities of wellbore two-phase flow and gas migration make direct measurements challenging, leading to potential inaccuracies in traditional modeling approaches. This study introduces a Data Assimilation (DA) technique, employing the Ensemble Kalman Filter (EnKF), to improve the real-time estimation of gas influx rates and distribution, thereby enhancing the accuracy of two-phase flow models in marine drilling.This research utilizes full-scale gas influx migration experiments conducted at Louisiana State University, where gas was injected from the bottom of an experimental well to simulate a riser gas event in a Water-based Mud (WBM) system. Key real-time measurements, including downhole pressure gauges at multiple depths and Distributed Acoustic Sensing (DAS) data, were employed to validate the estimated gas influx size and distribution within the riser using the EnKF. The overall gas influx distribution was captured through the real-time estimation of a dimensionless distribution index (DI), offering additional insights into the spatial characteristics of the migrating gas. Additionally, a Drift Flux Model (DFM) calibrated online through DA was used to predict flow parameters such as gas void fraction profiles within the riser during migration. The validation of these predictions demonstrated a strong correlation between the estimated and measured values.The outcomes of this study underscore the effectiveness of the proposed method in estimating parameters that are otherwise difficult to measure directly, thereby improving the predictive accuracy of gas influx behavior in marine drilling risers. This method offers significant practical value by enhancing real-time decision-making and risk management in marine drilling operations that involve gas migration, contributing to the broader goals of offshore drilling safety and marine environment protection.

Definition of minimum clearance height of railway bridges in a windblown sand area based on numerical simulation.

Railway bridges with lower beam bottom clearances in windblown sand areas tend to accumulate sand particles on the sides of the beams, which seriously impacts railway safety. To investigate the effect of beam clearance height on wind-sand movement near the surface, and to determine the minimum clearance height for railway bridges in such areas, computational fluid dynamics using the Euler-Euler two-phase flow model was employed to simulate the wind-sand flow field beneath bridges with different heights. The results indicated that as clearance height increased, both the high-speed area above the bridge and acceleration area under the bridge increased, while the turbulence area on the leeward side remained unchanged. Furthermore, wind speed on the windward side did not decrease, and no deceleration zone near the surface was observed with increased clearance height. When the bridge height reached 9m, the wind speed on the windward side no longer decreased. The correlation coefficients of near-surface wind speed under the bridge height of 9m and above were consistent. As wind speed increased, the fluctuations in wind speed between bridges with different clearance heights became more pronounced, with differing variation trends. On the leeward side, lower clearance heights resulted in greater wind speed fluctuation. With higher wind speeds, the main position of wind speed deceleration moved further from the bridge. Therefore, the clearance height of bridges in the windblown area should be at least 9m. These results provide a theoretical basis for the survey and design of bridges in the windblown sand areas.

Numerical simulation and experimental study of the flow heat transfer characteristics of rectangular micro-grooved ultra-thin flat plate heat pipes

Ultra-thin flat heat pipes (UTFPs) effectively address the heat dissipation challenges of contemporary compact electronic devices, owing to their superior thermal conductivity and high stability in confined places. This paper established the VOF vapor-liquid two-phase flow model of the rectangular micro-grooved ultra-thin flat heat pipe (M-UTFP) and constructed a test platform for evaluating the heat transfer performance of heat pipes, incorporating various filling rates (30%, 35%, 40%, 45%) and heat fluxes (0.375 × 106 W/m2, 0.5 × 106 W/m2, 1 × 106 W/m2, 1.25 × 106 W/m2, 1.67 × 106 W/m2). The findings indicated that the phase transition initially transpires on the heating surface of the evaporation section, while the vapor on the wall of the condensing section generates a liquid film after condensation. The optimal liquid filling rate for the M-UTFP was 35%. A heat flux of 1 × 106 W/m2 maintained a stable temperature fluctuation in the evaporation section of the heat pipe, thereby enhancing heat transfer efficiency. These findings align with simulation results, offering data references and design principles for the development of ultra-thin electronic cooling systems, such as those used in chips, and extending the application scope of UTFPs.

Dust concentration distribution and analysis of influencing factors in the heading face of Shangwan coal mine

Dust concentration in coal mine roadways significantly affects worker safety and health. Effective dust control is critical for optimizing the mine ventilation system and creating a safer working environment. This study investigates the impact of ventilation duct arrangements on dust concentration in a heading face, aiming to identify the optimal configurations for minimizing dust levels and enhancing worker safety. Using numerical simulations based on the gas-solid two-phase flow model in Fluent, we analyzed the effects of varying duct outlet distances and heights on airflow patterns and dust dispersion. Mesh generation, grid independence verification, and detailed parameter settings ensured accuracy and reliability of the simulation results. Results indicate that positioning the duct outlet 8 m from the heading face reduces dust concentration to approximately 39 mg/m³, while setting the duct height at 1.5 m notably decreases dust levels in the worker breathing zone. A mesh density of 576,449 cells ensured convergence and computational efficiency with an error margin within 2%. The findings provide practical insights into ventilation system optimization for coal mine heading faces, contributing to improved occupational health and operational safety. Future research should focus on validating these results through field experiments and addressing complex real-world conditions.

Influence of Ice Growth Mode on the Ice Thickness and Shape Prediction of Two-Dimensional Airfoil

Computational results of aircraft icing and predictions of ice shape are not only determined by the solutions of air-supercooled droplet two-phase flow and icing thermodynamic models of surface water film, but are also influenced by the growth mode of the ice layer. Two ice growth modes were established in a two-dimensional (2D) icing process simulation framework to calculate the ice thickness and ice shape, depending on whether surface deformation of the icing process was considered. Ice accretion simulations were performed with the two ice growth modes for an NACA0012 airfoil under rime ice and mixed ice conditions, and the results of ice amount, ice thickness, and ice shape were compared and analyzed. Under the same amount of ice formation, the ice thickness and ice shape obtained using different ice growth modes vary. The ice thickness and the ice shape size are relatively large without considering surface deformation, whereas the results with growth correction show a certain degree of reduction, which is more noticeable around the leading edge and the ice horns. However, the degrees of difference in ice thickness and ice shape are not the same, and the deviation in ice thickness is more obvious. Furthermore, the ice thickness and ice shape obtained using the ice growth correction mode are more consistent with experimental data and commercial software results, verifying the accuracy of the ice simulation method and the necessity of considering ice surface deformation. This paper is an essential guide for understanding the icing mechanism and accurately predicting two-dimensional ice shape.

Numerical Investigation of Water Transport and Effective Electrical Conductivity in Perforation of Gas Diffusion Layer Using Lattice Boltzmann Method

In polymer electrolyte membrane fuel cells, the gas diffusion layer (GDL) is composed of porous media and serves a critical role as a mass transport layer, facilitating reactant gas diffusion, removal of water generated in the catalyst layer, and electron transport. Artificial spacings known as perforations can be introduced to improve water management within this mass transport system. However, the impact of these perforations on the effective electrical conductivity has not been adequately studied. This study employs numerical methods to investigate water management and effective electrical conductivity in the presence of perforations, aiming to provide indicators for optimal design. The pseudopotential lattice Boltzmann method is utilized, which is particularly advantageous for modeling two-phase flow and electron transport in complex geometries. Using this numerical approach, we analyze water penetration in GDL structures and effective electrical conductivity based on electric potential fields focusing on geometric parameters such as the perforation size. Our results demonstrate a relationship between water management efficiency and effective electrical conductivity, suggesting the existence of an optimal perforation diameter. Moreover, when there is a water-induced penetration pattern due to the perforated structure, both the effective electrical conductivity and water management are enhanced at a lower porosity of the GDL structure.

Research on water flow characteristics and stress around bridges during floods

ABSTRACT Due to the frequent threat of floods to structures and engineering construction in rivers, in order to study the impact characteristics of river hydrodynamics on structures under excessive flow during floods, this study takes Jiefang Bridge as an example and uses the fluid volume two-phase flow model (VOF) in computational fluid dynamics (CFD), combined with advanced geometric reconstruction techniques such as iso Advector method, to simulate the dynamic changes of gas-liquid interface in the river. On the premise of guaranteeing the independence of the grid, the high precision structure grid is used for numerical simulation. The results indicate that when a flood contacts a bridge, the force on the bridge rapidly increases and fluctuates, reaching a significant peak of over 6,000,000 N. Bridge piers have a significant hindering effect on floods, and their impact gradually expands over time. Vorticity and turbulence energy analysis indicate the presence of strong flow disturbances around the bridge pier. In addition, the characteristics of the contact surface between water flow and bridges also significantly affect the stress and flow characteristics of bridges. Especially at a 45° angle of attack, the force on the bridge decreases, but the wake velocity increases.

A low Mach number diffuse-interface model for multicomponent two-phase flows with phase change

A low Mach number diffuse-interface model for multicomponent two-phase flows with phase change

Interior Ballistic Calculation and Analysis of Sudden Change of Motion Resistance of a Caliber Projectile in Bore

Abstract In this paper, three models are established to analyze and calculate the bore explosion phenomenon of a gun, namely, constant volume combustion model, classical interior ballistic model and one-dimensional two-phase flow. From the calculation results, the one-dimensional two-phase flow model has the largest calculation value, followed by the constant volume combustion model, while the classical interior ballistic calculation value is the smallest, and the one-dimensional two-phase flow model considers the situation closer to the actual situation. The calculation results of one-dimensional two-phase flow model show that the lag of the projectile will form a certain pressure shock behind the projectile, and the amplitude of the shock is negatively correlated with the decrease of the lag speed. In this accident, because the propellant basically burns, the pressure oscillation belongs to pure gas phase oscillation, and it does not produce abnormal pressure pulse and acceleration oscillation at the bottom of the projectile, but gradually converges, which does not cause the main charge of the projectile to detonate in the bore.