The paper presents the implementation of non-Newtonian fluid properties for compressible multiphase solver in the open source framework OpenFOAM. The transport models for Power Law, Cross Power Law, Casson, Bird-Carre...The paper presents the implementation of non-Newtonian fluid properties for compressible multiphase solver in the open source framework OpenFOAM. The transport models for Power Law, Cross Power Law, Casson, Bird-Carreau and Herschel-Bulkley fluids were included in the thermophysical model library. Appropriate non-Newtonian liquids have been chosen from literature, and pressure driven test simulations are carried out. Therefore, the solver compressibleInterFoam is used to compute air-liquid mixture flows over a backward facing step. A validation of the novel models has been performed by means of a sample-based comparison of the strain rate viscosity relation. The theoretical rheological properties of the selected liquids agree well with the results of the simulated data.展开更多
This paper aims to tackle the calculation efficiency problem raised in the cavitation-flow simulation of the aviation centrifugal pump due to the fading-away interface resulting from the dissipation of numerics used i...This paper aims to tackle the calculation efficiency problem raised in the cavitation-flow simulation of the aviation centrifugal pump due to the fading-away interface resulting from the dissipation of numerics used in the phase-change control equation for unstructured-grid multiphase flow,and due to the limitation of flow time-step in whole flow regimes,the control equation of vapor–liquid two-phase flow considering cavitation mass transport is established firstly,modifying the momentum equation by introducing the surface tension,and adding the artificial convective flow to the phase equation to solve the numerical dissipation problem.Secondly,in consideration of the local time step principle and based on the multi-dimensional general limiter algorithm with explicit solutions under the OpenFOAM platform,a solution method of steady-state VOF (Volume of Fluid) model considering cavitation two-phase change is constructed,and the feasibility of this method is verified by NACA hydrofoil and NASA flat plate inducer.Finally,based on the platform developed,the cavitation performance of an aviation centrifugal pump inducer is analyzed.The research results show that the error of the calculated cavitation pressure distribution for NACA hydrofoil between the simulation test and the experimental-test is less than 5%,and the maximum error of calculated cavitation number at pump head dropping for NASA high-speed flat plate inducer between the simulation test and the experimental-test is 2.1%.The cavitation area observed in the simulation test is the same as that obtained in the high-speed photography test.Based on the OpenFOAM simulation method,the position of pump head dropping of the fuel centrifugal pump can be accurately captured.The error of the calculated cavitation number at pump head dropping between the simulation test and the experimental test is about 3.7%,showing high calculation accuracy.展开更多
The modulation of turbulence by particles has been rigorously investigated in the literature yielding either a reduction or an enhancement of the turbulent kinetic energy at different spatial length scales.However,a g...The modulation of turbulence by particles has been rigorously investigated in the literature yielding either a reduction or an enhancement of the turbulent kinetic energy at different spatial length scales.However,a general description of the turbulence modulation in multiphase flows due to the presence of an interphase force has attracted less attention.In this paper,we investigate the turbulent modulation for interfacial and fluid-particle flows analytically and numerically,where surface tension and drag define the interphase coupling,respectively.It is shown that surface tension and drag appear as additional production/dissipation terms in the transport equations for the turbulent kinetic energies(TKE),which is of particular importance for the turbulence modelling of multiphase flows.Furthermore,we study the modulation of turbulence in decaying homogenous isotropic turbulence(HIT)for both types of multiphase flow.The results clearly unveil that in both cases the energy is reduced at large scales,while the small-scale energy is enhanced compared to single-phase flows.Particularly,at large scales surface tension works against the turbulent eddies and hinders the ejection of droplet from the corrugated interface.In contrast,at the small scales,the surface tension force and the velocity fluctuations are aligned leading to an enhancement of the energy.In the case of fluid-particle flows,particles retain their energy longer than the surrounding fluid increasing the energy at the small scales,while at the large scales the particles do not follow exactly the surrounding fluid reducing its energy.For the latter effect,a considerable dependence on the particle Stokes number is found.展开更多
Computational fluid dynamics (CFD) analysis of single- phase and two-phase flow was performed in a 90 degree horizontal to vertical elbow with 12.7 mm inside diameter. Characteristic flow behavior was investigated at ...Computational fluid dynamics (CFD) analysis of single- phase and two-phase flow was performed in a 90 degree horizontal to vertical elbow with 12.7 mm inside diameter. Characteristic flow behavior was investigated at six different upstream and downstream locations of the elbow. To evaluate the effects of different phases, three different air veloci-ties and three different water velocities were used during this study. Commercial CFD code FLUENT was used to perform analysis of both single and multiphase flows. Pressure and velocity profiles at six locations showed an increase in pressure at the elbow geometry with decreasing pressure as fluid leaves from the elbow. Pressure drop behavior observed to be similar for single-phase and multiphase flows. Comparison of CFD results with available empirical models showed reasonably good agreement.展开更多
The multiphase flow in a Peirce-Smith copper converter is numerically explored in this work. Molten matte, molten slag and air are the phases considered. The transient partial differential equations that constitute th...The multiphase flow in a Peirce-Smith copper converter is numerically explored in this work. Molten matte, molten slag and air are the phases considered. The transient partial differential equations that constitute the mathematical model are discretized using a two-dimensional computational mesh. The Computational Fluid Dynamics technique is employed to numerically solve the discretized equations. The aim of the numerical analysis is to study the influence of the nozzle height on the phase distributions inside the converter. Three values of the nozzle heights are considered.展开更多
An unsteady numerical simulation is conducted to examine the dynamic runback characteristics of a water film flow driven by a boundary layer airflow over a solid surface pertinent to the dynamic glaze ice accretion pr...An unsteady numerical simulation is conducted to examine the dynamic runback characteristics of a water film flow driven by a boundary layer airflow over a solid surface pertinent to the dynamic glaze ice accretion process over aircraft wing surfaces.The multiphase flow simulation results of the wind-driven water runback(WDWR)flow are compared quantitatively with the experimental results in terms of the time-dependent variations of the water film thickness profiles and evolution of the front contact point of the runback water film flow.The underlying mechanism of the intermittent water runback behavior is elucidated by analyzing the time evolution of the airflow velocity and vorticity fields above the runback water film flow over the solid surface.To the best knowledge of the authors,the work presented here is the first successful attempt to numerically examine the transient runback characteristics of WDWR flows.It serves as an excellent benchmark case for the development of best practices to model the important micro-physical processes responsible for the transient water transport over aircraft wing surfaces.展开更多
Numerical investigation of the dusty Williamson fluid with the dependency of time has been done in current disquisition. The flow of multiphase liquid/particle suspension saturating the medium is caused by stretching ...Numerical investigation of the dusty Williamson fluid with the dependency of time has been done in current disquisition. The flow of multiphase liquid/particle suspension saturating the medium is caused by stretching of porous surface. The influence of magnetic field and heat generation/absorption is observed. It is assumed that particle has a spherical shape and distributed uniformly in fluid matrix. The unsteady two-dimensional problems are modeled for both fluid and particle phase using conservation of mass, momentum and heat transfer. The finalized model generates the non-dimensioned parameters, namely Weissenberg number, unsteadiness parameter, magnetic parameter,heat generation/absorption parameter, Prandtl number, fluid particle interaction parameter, and mass concentration parameters. The numerical solution is obtained. Locality of skin friction and Nusselt number is deliberately focused to help of tables and graphs. While inferencing the current article it is clearly observed that increment of Williamson parameter, unsteadiness parameter, magnetic parameter, volume fraction parameter, and mass concentration parameter reduces the velocity profile of fluid and solid particles as well. And increment of Prandtl number, unsteadiness parameter,volume fraction parameter, and mass concentration parameter reduces the temperature profile of fluid and solid particles as well.展开更多
The secondary flow driven by the primary vortex in a cylinder,generating the so called"tea leaf paradox",is fundamental for understanding many natural phenomena,industrial applications and scientific researc...The secondary flow driven by the primary vortex in a cylinder,generating the so called"tea leaf paradox",is fundamental for understanding many natural phenomena,industrial applications and scientific researches.In this work,the effect of wettability on the primary vortex and secondary flow is investigated by the three-dimensional multiphase lattice Boltzmann method based on a chemical potential.We find that the surface wettability strongly affects the shape of the primary vortex.With the increase of the contact angle of the cylinder,the sectional plane of the primary vortex gradually changes from a steep valley into a saddle with two raised parts.Because the surface friction is reduced correspondingly,the core of the secondary vortex moves to the centerline of the cylinder and the vortex intensity also increases.The stirring force has stronger effects to enhance the secondary flow and push the vortex up than the surface wettability.Interestingly,a small secondary vortex is discovered near the three-phase contact line when the surface has a moderate wettability,owing to the interaction between the secondary flow and the curved gas/liquid interface.展开更多
The main contribution of this work is a comprehensive overview of the many years of research on various inter-facial forces with distinct flow structure transitions in liquid-gas multiphase flow in vertical columns.In...The main contribution of this work is a comprehensive overview of the many years of research on various inter-facial forces with distinct flow structure transitions in liquid-gas multiphase flow in vertical columns.Injecting a gas phase into a liquid phase result in a fluid dynamic phenomenology that is substantial,magnetizing,and fascinating.Bubble columns modelling functioning in the bubbly,slug,churn,and annular turbulent flow regime is a major challenge due to their complicated and ephemeral nature.An important modelling choice is how to represent the bubble size distribution.This may be accomplished in several ways,from the relatively simple one of utilizing a single representative bubble size to more intricate techniques.To evaluate the computational findings,we have analysed and discussed several turbulence models in this comparative research.Furthermore,this review summarises the current inter-facial force models,which include turbulent dispersion force,lift force,drag force,wall lubrication force,and virtual mass force.The models of Grace,Tomiyama,Zuber,Antel,Legendre,Burns,and Naumann universal Hosokawa are used,respectively.展开更多
Noncohesive particle clusters are identified and tracked in turbulent flows to determine the breakdown and time evolution of cluster statistics and their implications for interscale mass transfer,which has connections...Noncohesive particle clusters are identified and tracked in turbulent flows to determine the breakdown and time evolution of cluster statistics and their implications for interscale mass transfer,which has connections to the classical turbulent energy cascade and its mass cascade counterpart running in parallel.In particular,the formation and dynamics of sediment and larvae clusters are of interest to coral larvae settlement in coastal regions and particularly the resilience of green-gray coastal protection solutions.Analogous cluster behavior is relevant to cloud microphysics and precipitation initiation,radiation transport and light transmission through colloids and suspensions,heat and mass transfer in particle-laden flows,and viral and pollutant transmission.Following a comparison between various clustering techniques,we adopt a density-based cluster identification algorithm based on its simplicity and efficiency,where particles are clustered based on the number of neighboring particles in their individual spheres of influence.We establish parallels with lattice-based percolation theory,as evident in the power-law scaling of the cluster size distribution near the percolation threshold.The degree of discontinuity of the phase transition associated with this percolation threshold is observed to broaden with larger Stokes numbers and thereby large-scale clustering.The sensitivity of our findings to the employed clustering algorithm is discussed.A novel cluster tracking algorithm is deployed to determine the interscale transfer rate along the particle-number phase-space dimension via accounting of cluster breakup and merger events,extending previous work on the bubble breakup cascade beneath surface breaking waves.Our findings shed light on the interaction between particle clusters and their carrier turbulent flows,with an eye toward transport models incorporating cluster characteristics and dynamics.展开更多
In this article we use analytical and numerical modeling to describe parallel viscous two-phase flows in microchannels.The focus is on idealized two-dimensional geometries,with a view to validating the various methodo...In this article we use analytical and numerical modeling to describe parallel viscous two-phase flows in microchannels.The focus is on idealized two-dimensional geometries,with a view to validating the various methodologies for future work in three dimensions.In the first instance,we use analytical Orr-Sommerfeld theory to describe the linear instability which governs the formation of small-amplitude waves in such systems.We then compare the results of this analysis with an in-house Computational Fluid Dynamics(CFD)solver called TPLS.Excellent agreement between the theoretical analysis and TPLS is obtained in the regime of small-amplitude waves.We continue the numerical simulations beyond the point of validity of the Orr-Sommerfeld theory.In this way,we illustrate the generation of nonlinear interfacial waves and reverse entrainment of one fluid phase into the other.We justify our simulations further by comparing the numerical results with corresponding results from a commercial CFD code.This comparison is again extremely favourable—this rigorous validation paves the way for future work using TPLS or commercial codes to perform extremely detailed three-dimensional simulations of flow in microchannels.展开更多
Numerical study of multiphase fluid flows require mathematical methods for distinguishing interface between two fluids.The volume of fluid(VOF)method is one of such method which takes care of fluid shape in a local do...Numerical study of multiphase fluid flows require mathematical methods for distinguishing interface between two fluids.The volume of fluid(VOF)method is one of such method which takes care of fluid shape in a local domain and reconstructs the interface from volume fraction of one fluid.Maintaining sharp interface during reconstruction is a challenging task and geometrical approach of VOF method better suits for incompressible fluids.This paper provides a complete mathematical discussion of extended form of VOF method using a approach known as piecewise linear interface calculation(PLIC).An analytical relation between volume fraction and interface position has been explored with the help of primitive geometrical shapes.The method with this analytical relation has been applied to multiphase fluid flow benchmark problems and found to be in good agreement.展开更多
A conservative modification to the ghost fluid method(GFM)is developed for compressible multiphase flows.The motivation is to eliminate or reduce the conservation error of the GFM without affecting its performance.We ...A conservative modification to the ghost fluid method(GFM)is developed for compressible multiphase flows.The motivation is to eliminate or reduce the conservation error of the GFM without affecting its performance.We track the conservative variables near the material interface and use this information to modify the numerical solution for an interfacing cell when the interface has passed the cell.The modification procedure can be used on the GFM with any base schemes.In this paper we use the fifth order finite difference WENO scheme for the spatial discretization and the third order TVD Runge-Kutta method for the time discretization.The level set method is used to capture the interface.Numerical experiments show that the method is at least mass and momentum conservative and is in general comparable in numerical resolution with the original GFM.展开更多
This work proposes a vibrating mesh screen as an alternative to the static mesh screen currently used in conventional flooded-bed dust scrubbers for removing airborne coal mine dust in the continuous mining environmen...This work proposes a vibrating mesh screen as an alternative to the static mesh screen currently used in conventional flooded-bed dust scrubbers for removing airborne coal mine dust in the continuous mining environment.Fundamental assessments suggest that a vibrating screen may improve the dust collection efficiency of scrubber systems and mitigate the clogging issues associated with the conventional design.To evaluate this hypothesis,computational fluid dynamics(CFD)simulations were carried out to assess the effects of vibration conditions(i.e.,frequency and amplitude)on the dust particle-mesh interaction and mesh wetting conditions,which are the two decisive factors in determining the dust collection efficiency.The results suggest that the vibrating mesh screen can enhance dust particle collision opportunities on the mesh and increase mesh wetted area as compared to the static mesh screen.The effects of mesh screen aperture,coal dust concentration,and spray nozzle flow rate on the performance of the vibrating mesh are also evaluated.Finally,a simplified three-phase flow simulation including airflow,dust particles,and water droplet spray is performed,and the results reflect a significant improvement of dust collection efficiency in the liquid-coated vibrating mesh screen.展开更多
The metal components exposed to the high-velocity liquid-solid flow can be rapidly eroded by the accelerated particles.With an excellent combination of strength and toughness,the NiCoCrFeNb_(0.45)eutectic high-entropy...The metal components exposed to the high-velocity liquid-solid flow can be rapidly eroded by the accelerated particles.With an excellent combination of strength and toughness,the NiCoCrFeNb_(0.45)eutectic high-entropy alloy(EHEA)has emerged as a promising material to resist erosion damage.In this study,the erosion behavior of NiCoCrFeNb_(0.45)EHEA in high-velocity multiphase flow is investigated through the coupling analysis of material properties,multiphase flow,and particle–surface impact behavior.The inherent mathematical relationship is discovered between the erosion rates and the impact velocity,impact angle,and test time.The results show that the NiCoCrFeNb_(0.45)EHEA has superior erosion resistance than the commonly used machinery materials.The principal material removal mechanism is the formation and brittle fracture of the platelets,accompanied by micro-cutting and ploughing at some oblique angles.The higher work-hardenability of NiCoCrFeNb_(0.45)EHEA could mitigate the erosion damage as time proceeds,and this effect becomes more apparent as the impact angle increases.Therefore,the evolution of erosion damage with time varies significantly depending on the impact angle.Based on the test data and computational fluid dynamics(CFD)modeling of the near-wall flow field,a power exponential function relationship between erosion depth and the corresponding impact velocity at various locations on the material surface is established.展开更多
文摘The paper presents the implementation of non-Newtonian fluid properties for compressible multiphase solver in the open source framework OpenFOAM. The transport models for Power Law, Cross Power Law, Casson, Bird-Carreau and Herschel-Bulkley fluids were included in the thermophysical model library. Appropriate non-Newtonian liquids have been chosen from literature, and pressure driven test simulations are carried out. Therefore, the solver compressibleInterFoam is used to compute air-liquid mixture flows over a backward facing step. A validation of the novel models has been performed by means of a sample-based comparison of the strain rate viscosity relation. The theoretical rheological properties of the selected liquids agree well with the results of the simulated data.
基金supported by the National Science and Technology Major Project, China (No. J2019-V-0016-0111)the Aviation Engine and Gas Turbine Basic Science Center Project, China (No. P2022-B-V-003-001)+3 种基金the Defense Industrial Technology Development Program, China (No. JCKY2022607C002)the AECC Industry University Cooperation Project, China (No. HFZL2022CXY013)the National Natural Science Foundation of China (No. 52372396)the Key R&D Project in Shaanxi Province, China (No. 2021GXLH-01-16)。
文摘This paper aims to tackle the calculation efficiency problem raised in the cavitation-flow simulation of the aviation centrifugal pump due to the fading-away interface resulting from the dissipation of numerics used in the phase-change control equation for unstructured-grid multiphase flow,and due to the limitation of flow time-step in whole flow regimes,the control equation of vapor–liquid two-phase flow considering cavitation mass transport is established firstly,modifying the momentum equation by introducing the surface tension,and adding the artificial convective flow to the phase equation to solve the numerical dissipation problem.Secondly,in consideration of the local time step principle and based on the multi-dimensional general limiter algorithm with explicit solutions under the OpenFOAM platform,a solution method of steady-state VOF (Volume of Fluid) model considering cavitation two-phase change is constructed,and the feasibility of this method is verified by NACA hydrofoil and NASA flat plate inducer.Finally,based on the platform developed,the cavitation performance of an aviation centrifugal pump inducer is analyzed.The research results show that the error of the calculated cavitation pressure distribution for NACA hydrofoil between the simulation test and the experimental-test is less than 5%,and the maximum error of calculated cavitation number at pump head dropping for NASA high-speed flat plate inducer between the simulation test and the experimental-test is 2.1%.The cavitation area observed in the simulation test is the same as that obtained in the high-speed photography test.Based on the OpenFOAM simulation method,the position of pump head dropping of the fuel centrifugal pump can be accurately captured.The error of the calculated cavitation number at pump head dropping between the simulation test and the experimental test is about 3.7%,showing high calculation accuracy.
基金This work was supported by the Austrian Federal Ministry for Digital and Economic Affairs and the National Foundation for Research, Technology and Development. The authors further want to acknowledge the funding support of K1-MET GmbH, metallurgical competence center. The research programme of the K1-MET competence center is supported by COMET (Competence Center for Excellent Technologies), the Austrian programme for competence centers. COMET is funded by the Federal Ministry for Transport, Innovation and Technology, the Federal Ministry for Digital and Economic Affairs and the provinces of Upper Austria, Tyrol and Styria. Beside the public funding from COMET, this research project is partially financed by the industrial partners Primetals Technologies Austria GmbH, voestalpine Stahl Donawitz GmbH, RHI Magnesita GmbH and voestalpine Stahl GmbH.
文摘The modulation of turbulence by particles has been rigorously investigated in the literature yielding either a reduction or an enhancement of the turbulent kinetic energy at different spatial length scales.However,a general description of the turbulence modulation in multiphase flows due to the presence of an interphase force has attracted less attention.In this paper,we investigate the turbulent modulation for interfacial and fluid-particle flows analytically and numerically,where surface tension and drag define the interphase coupling,respectively.It is shown that surface tension and drag appear as additional production/dissipation terms in the transport equations for the turbulent kinetic energies(TKE),which is of particular importance for the turbulence modelling of multiphase flows.Furthermore,we study the modulation of turbulence in decaying homogenous isotropic turbulence(HIT)for both types of multiphase flow.The results clearly unveil that in both cases the energy is reduced at large scales,while the small-scale energy is enhanced compared to single-phase flows.Particularly,at large scales surface tension works against the turbulent eddies and hinders the ejection of droplet from the corrugated interface.In contrast,at the small scales,the surface tension force and the velocity fluctuations are aligned leading to an enhancement of the energy.In the case of fluid-particle flows,particles retain their energy longer than the surrounding fluid increasing the energy at the small scales,while at the large scales the particles do not follow exactly the surrounding fluid reducing its energy.For the latter effect,a considerable dependence on the particle Stokes number is found.
文摘Computational fluid dynamics (CFD) analysis of single- phase and two-phase flow was performed in a 90 degree horizontal to vertical elbow with 12.7 mm inside diameter. Characteristic flow behavior was investigated at six different upstream and downstream locations of the elbow. To evaluate the effects of different phases, three different air veloci-ties and three different water velocities were used during this study. Commercial CFD code FLUENT was used to perform analysis of both single and multiphase flows. Pressure and velocity profiles at six locations showed an increase in pressure at the elbow geometry with decreasing pressure as fluid leaves from the elbow. Pressure drop behavior observed to be similar for single-phase and multiphase flows. Comparison of CFD results with available empirical models showed reasonably good agreement.
文摘The multiphase flow in a Peirce-Smith copper converter is numerically explored in this work. Molten matte, molten slag and air are the phases considered. The transient partial differential equations that constitute the mathematical model are discretized using a two-dimensional computational mesh. The Computational Fluid Dynamics technique is employed to numerically solve the discretized equations. The aim of the numerical analysis is to study the influence of the nozzle height on the phase distributions inside the converter. Three values of the nozzle heights are considered.
基金supported by the National Science Foundation(NSF)of the USA(Grant Nos.TIP-2140489,CBET-2313310,and CBET-2415347).
文摘An unsteady numerical simulation is conducted to examine the dynamic runback characteristics of a water film flow driven by a boundary layer airflow over a solid surface pertinent to the dynamic glaze ice accretion process over aircraft wing surfaces.The multiphase flow simulation results of the wind-driven water runback(WDWR)flow are compared quantitatively with the experimental results in terms of the time-dependent variations of the water film thickness profiles and evolution of the front contact point of the runback water film flow.The underlying mechanism of the intermittent water runback behavior is elucidated by analyzing the time evolution of the airflow velocity and vorticity fields above the runback water film flow over the solid surface.To the best knowledge of the authors,the work presented here is the first successful attempt to numerically examine the transient runback characteristics of WDWR flows.It serves as an excellent benchmark case for the development of best practices to model the important micro-physical processes responsible for the transient water transport over aircraft wing surfaces.
文摘Numerical investigation of the dusty Williamson fluid with the dependency of time has been done in current disquisition. The flow of multiphase liquid/particle suspension saturating the medium is caused by stretching of porous surface. The influence of magnetic field and heat generation/absorption is observed. It is assumed that particle has a spherical shape and distributed uniformly in fluid matrix. The unsteady two-dimensional problems are modeled for both fluid and particle phase using conservation of mass, momentum and heat transfer. The finalized model generates the non-dimensioned parameters, namely Weissenberg number, unsteadiness parameter, magnetic parameter,heat generation/absorption parameter, Prandtl number, fluid particle interaction parameter, and mass concentration parameters. The numerical solution is obtained. Locality of skin friction and Nusselt number is deliberately focused to help of tables and graphs. While inferencing the current article it is clearly observed that increment of Williamson parameter, unsteadiness parameter, magnetic parameter, volume fraction parameter, and mass concentration parameter reduces the velocity profile of fluid and solid particles as well. And increment of Prandtl number, unsteadiness parameter,volume fraction parameter, and mass concentration parameter reduces the temperature profile of fluid and solid particles as well.
基金Supported by the National Natural Science Foundation of China under Grant Nos.11862003,81860635,11462003the Key Project of Guangxi Natural Science Foundation under Grant No.2017GXNSF DA198038Guangxi “Bagui Scholar” Teams for Innovation and Research Project
文摘The secondary flow driven by the primary vortex in a cylinder,generating the so called"tea leaf paradox",is fundamental for understanding many natural phenomena,industrial applications and scientific researches.In this work,the effect of wettability on the primary vortex and secondary flow is investigated by the three-dimensional multiphase lattice Boltzmann method based on a chemical potential.We find that the surface wettability strongly affects the shape of the primary vortex.With the increase of the contact angle of the cylinder,the sectional plane of the primary vortex gradually changes from a steep valley into a saddle with two raised parts.Because the surface friction is reduced correspondingly,the core of the secondary vortex moves to the centerline of the cylinder and the vortex intensity also increases.The stirring force has stronger effects to enhance the secondary flow and push the vortex up than the surface wettability.Interestingly,a small secondary vortex is discovered near the three-phase contact line when the surface has a moderate wettability,owing to the interaction between the secondary flow and the curved gas/liquid interface.
基金supported by the National Science Foundation for Distinguished Young Scholars of China(No.52425903)the National Natural Science Foundation of China(No U2106225)Jiangsu Excellent Post-doctoral Program(2023ZB890).
文摘The main contribution of this work is a comprehensive overview of the many years of research on various inter-facial forces with distinct flow structure transitions in liquid-gas multiphase flow in vertical columns.Injecting a gas phase into a liquid phase result in a fluid dynamic phenomenology that is substantial,magnetizing,and fascinating.Bubble columns modelling functioning in the bubbly,slug,churn,and annular turbulent flow regime is a major challenge due to their complicated and ephemeral nature.An important modelling choice is how to represent the bubble size distribution.This may be accomplished in several ways,from the relatively simple one of utilizing a single representative bubble size to more intricate techniques.To evaluate the computational findings,we have analysed and discussed several turbulence models in this comparative research.Furthermore,this review summarises the current inter-facial force models,which include turbulent dispersion force,lift force,drag force,wall lubrication force,and virtual mass force.The models of Grace,Tomiyama,Zuber,Antel,Legendre,Burns,and Naumann universal Hosokawa are used,respectively.
文摘Noncohesive particle clusters are identified and tracked in turbulent flows to determine the breakdown and time evolution of cluster statistics and their implications for interscale mass transfer,which has connections to the classical turbulent energy cascade and its mass cascade counterpart running in parallel.In particular,the formation and dynamics of sediment and larvae clusters are of interest to coral larvae settlement in coastal regions and particularly the resilience of green-gray coastal protection solutions.Analogous cluster behavior is relevant to cloud microphysics and precipitation initiation,radiation transport and light transmission through colloids and suspensions,heat and mass transfer in particle-laden flows,and viral and pollutant transmission.Following a comparison between various clustering techniques,we adopt a density-based cluster identification algorithm based on its simplicity and efficiency,where particles are clustered based on the number of neighboring particles in their individual spheres of influence.We establish parallels with lattice-based percolation theory,as evident in the power-law scaling of the cluster size distribution near the percolation threshold.The degree of discontinuity of the phase transition associated with this percolation threshold is observed to broaden with larger Stokes numbers and thereby large-scale clustering.The sensitivity of our findings to the employed clustering algorithm is discussed.A novel cluster tracking algorithm is deployed to determine the interscale transfer rate along the particle-number phase-space dimension via accounting of cluster breakup and merger events,extending previous work on the bubble breakup cascade beneath surface breaking waves.Our findings shed light on the interaction between particle clusters and their carrier turbulent flows,with an eye toward transport models incorporating cluster characteristics and dynamics.
文摘In this article we use analytical and numerical modeling to describe parallel viscous two-phase flows in microchannels.The focus is on idealized two-dimensional geometries,with a view to validating the various methodologies for future work in three dimensions.In the first instance,we use analytical Orr-Sommerfeld theory to describe the linear instability which governs the formation of small-amplitude waves in such systems.We then compare the results of this analysis with an in-house Computational Fluid Dynamics(CFD)solver called TPLS.Excellent agreement between the theoretical analysis and TPLS is obtained in the regime of small-amplitude waves.We continue the numerical simulations beyond the point of validity of the Orr-Sommerfeld theory.In this way,we illustrate the generation of nonlinear interfacial waves and reverse entrainment of one fluid phase into the other.We justify our simulations further by comparing the numerical results with corresponding results from a commercial CFD code.This comparison is again extremely favourable—this rigorous validation paves the way for future work using TPLS or commercial codes to perform extremely detailed three-dimensional simulations of flow in microchannels.
基金supported by Faculty of Engineering and Computing,Dublin City University,Ireland through its CONNECT grant.
文摘Numerical study of multiphase fluid flows require mathematical methods for distinguishing interface between two fluids.The volume of fluid(VOF)method is one of such method which takes care of fluid shape in a local domain and reconstructs the interface from volume fraction of one fluid.Maintaining sharp interface during reconstruction is a challenging task and geometrical approach of VOF method better suits for incompressible fluids.This paper provides a complete mathematical discussion of extended form of VOF method using a approach known as piecewise linear interface calculation(PLIC).An analytical relation between volume fraction and interface position has been explored with the help of primitive geometrical shapes.The method with this analytical relation has been applied to multiphase fluid flow benchmark problems and found to be in good agreement.
基金supported by NSFC 10531080,10972230,and 973 project 2005CB321703 and 2010CB731505supported by ARO grant W911NF-08-1-0520 and NSF grant DMS-0809086.
文摘A conservative modification to the ghost fluid method(GFM)is developed for compressible multiphase flows.The motivation is to eliminate or reduce the conservation error of the GFM without affecting its performance.We track the conservative variables near the material interface and use this information to modify the numerical solution for an interfacing cell when the interface has passed the cell.The modification procedure can be used on the GFM with any base schemes.In this paper we use the fifth order finite difference WENO scheme for the spatial discretization and the third order TVD Runge-Kutta method for the time discretization.The level set method is used to capture the interface.Numerical experiments show that the method is at least mass and momentum conservative and is in general comparable in numerical resolution with the original GFM.
基金sponsored by the Alpha Foundation for the Improvement of Mine Safety and Health, Inc. (Alpha Foundation)
文摘This work proposes a vibrating mesh screen as an alternative to the static mesh screen currently used in conventional flooded-bed dust scrubbers for removing airborne coal mine dust in the continuous mining environment.Fundamental assessments suggest that a vibrating screen may improve the dust collection efficiency of scrubber systems and mitigate the clogging issues associated with the conventional design.To evaluate this hypothesis,computational fluid dynamics(CFD)simulations were carried out to assess the effects of vibration conditions(i.e.,frequency and amplitude)on the dust particle-mesh interaction and mesh wetting conditions,which are the two decisive factors in determining the dust collection efficiency.The results suggest that the vibrating mesh screen can enhance dust particle collision opportunities on the mesh and increase mesh wetted area as compared to the static mesh screen.The effects of mesh screen aperture,coal dust concentration,and spray nozzle flow rate on the performance of the vibrating mesh are also evaluated.Finally,a simplified three-phase flow simulation including airflow,dust particles,and water droplet spray is performed,and the results reflect a significant improvement of dust collection efficiency in the liquid-coated vibrating mesh screen.
基金supported by the National Natural Science Foundation of China(Nos.51906200,51879216)the Key Project of National Natural Science Foundation of China(No.51839010)+1 种基金the Key Laboratory Foundation of Education Department of Shaanxi(No.19JS045)the China Postdoctoral Science Foundation(Nos.2019TQ0248,2019M663735)。
文摘The metal components exposed to the high-velocity liquid-solid flow can be rapidly eroded by the accelerated particles.With an excellent combination of strength and toughness,the NiCoCrFeNb_(0.45)eutectic high-entropy alloy(EHEA)has emerged as a promising material to resist erosion damage.In this study,the erosion behavior of NiCoCrFeNb_(0.45)EHEA in high-velocity multiphase flow is investigated through the coupling analysis of material properties,multiphase flow,and particle–surface impact behavior.The inherent mathematical relationship is discovered between the erosion rates and the impact velocity,impact angle,and test time.The results show that the NiCoCrFeNb_(0.45)EHEA has superior erosion resistance than the commonly used machinery materials.The principal material removal mechanism is the formation and brittle fracture of the platelets,accompanied by micro-cutting and ploughing at some oblique angles.The higher work-hardenability of NiCoCrFeNb_(0.45)EHEA could mitigate the erosion damage as time proceeds,and this effect becomes more apparent as the impact angle increases.Therefore,the evolution of erosion damage with time varies significantly depending on the impact angle.Based on the test data and computational fluid dynamics(CFD)modeling of the near-wall flow field,a power exponential function relationship between erosion depth and the corresponding impact velocity at various locations on the material surface is established.
