This study is to numerically test the interfacial instability of ferrofluid flow under the presence of a vacuum magnetic field.The ferrofluid parabolized stability equations(PSEs)are derived from the ferrofluid stabil...This study is to numerically test the interfacial instability of ferrofluid flow under the presence of a vacuum magnetic field.The ferrofluid parabolized stability equations(PSEs)are derived from the ferrofluid stability equations and the Rosensweig equations,and the characteristic values of the ferrofluid PSEs are given to describe the ellipticity of ferrofluid flow.Three numerical models representing specific cases considering with/without a vacuum magnetic field or viscosity are created to mathematically examine the interfacial instability by the computation of characteristic values.Numerical investigation shows strong dependence of the basic characteristic of ferrofluid Rayleigh-Taylor instability(RTI)on viscosity of ferrofluid and independence of the vacuum magnetic field.For the shock wave striking helium bubble,the magnetic field is not able to trigger the symmetry breaking of bubble but change the speed of the bubble movement.In the process of droplet formation from a submerged orifice,the collision between the droplet and the liquid surface causes symmetry breaking.Both the viscosity and the magnetic field exacerbate symmetry breaking.The computational results agree with the published experimental results.展开更多
The classical linear instability theory was applied to the planar stratified two_layers flow with high speed compressible gas layer impacting on incompressible viscous liquid layer. The walls were kept at different te...The classical linear instability theory was applied to the planar stratified two_layers flow with high speed compressible gas layer impacting on incompressible viscous liquid layer. The walls were kept at different temperatures, resulting in heat transfer across the layers. The thermal conductivity and the density of the gas were alerted when the temperature changes.After some treatment, a four_order stiff ordinary differential equation was derived,and numerical integration and multi_shooting method were used to solve this equation for its spatial mode calculation. The numerical results of characteristic parameters show good coincidence with other models. At the same time, when the wall temperature ratio decreases,as well as the Reynolds number and the gas thermal conductivity change increases, the atomization would be more efficient and producing finer droplets. And the results show good fit with the experimental datum of HJE. Co. Inc (Glens Falls, NY, USA).展开更多
Inspired by recent research interest in the interface wrinkling of bonded materials in diverse areas of 3D printing,the present work studies the interfacial instability of two bonded elastic bodies driven by negative ...Inspired by recent research interest in the interface wrinkling of bonded materials in diverse areas of 3D printing,the present work studies the interfacial instability of two bonded elastic bodies driven by negative interfacial tension or compressible bulk residual stress.For interfacial instability modes decaying exponentially with distance from the interface,the present model is formulated for two bonded elastic half-spaces with a planar interface under plane strain.An explicit expression is given for the wavenumber of interfacial instability driven by negative interfacial tension,and a critical condition is derived for interfacial instability driven by compressive bulk residual stress.The derived results are validated with comparison to known results on surface instability of an elastic half-space,and the role of shear modulus ratio and Poisson’s ratios of two bonded elastic bodies in interfacial instability,an issue to be addressed in literature,is studied with specific reference to material parameters used in some areas of 3D printing.展开更多
The problem of nonlinear instability of interfacial waves between two immiscible conducting cylindrical fluids of a weak Oldroyd 3-constant kind is studied. The system is assumed to be influenced by an axial magnetic ...The problem of nonlinear instability of interfacial waves between two immiscible conducting cylindrical fluids of a weak Oldroyd 3-constant kind is studied. The system is assumed to be influenced by an axial magnetic field, where the effect of surface tension is taken into account. The analysis, based on the method of multiple scale in both space and time, includes the linear as well as the nonlinear effects. This scheme leads to imposing of two levels of the solvability conditions, which are used to construct like-nonlinear Schr6dinger equations （1-NLS） with complex coefficients. These equations generally describe the competition between nonlinearity and dispersion. The stability criteria are theoret- ically discussed and thereby stability diagrams are obtained for different sets of physical parameters. Proceeding to the nonlinear step of the problem, the results show the appearance of dual role of some physical parameters. Moreover, these effects depend on the wave kind, short or long, except for the ordinary viscosity parameter. The effect of the field on the system stability depends on the existence of viscosity and differs in the linear case of the problem from the nonlinear one. There is an obvious difference between the effect of the three Oldroyd constants on the system stability. New instability regions in the parameter space, which appear due to nonlinear effects, are shown.展开更多
This review summarizes recent progress in the study of impinging-jet dynamics and atomization,with a focus on liquid sheet formation,instability mechanisms,and the influence of key parameters such as fluid properties,...This review summarizes recent progress in the study of impinging-jet dynamics and atomization,with a focus on liquid sheet formation,instability mechanisms,and the influence of key parameters such as fluid properties,Weber number,and Reynolds number.Special attention is given to atomization behaviors under high pressure and external perturbations.Representative experimental and numerical approaches are introduced,and critical findings under complex conditions are highlighted.In addition,practical applications of impinging-jet technology in aerospace propulsion,biomedical devices,and energy science are discussed.This review aims to serve as a concise reference for researchers interested in multiphase flow dynamics and engineering applications of impinging jets.展开更多
Based on multi-fluid volume fraction and piecewise parabolic method （PPM）, a multi-viscosity-fluid hydrodynamic code MVPPM （Multi-Viscosity-Fluid Piecewise Parabolic Method） is developed and applied to the problem...Based on multi-fluid volume fraction and piecewise parabolic method （PPM）, a multi-viscosity-fluid hydrodynamic code MVPPM （Multi-Viscosity-Fluid Piecewise Parabolic Method） is developed and applied to the problems of shock-induced hydrodynamic interfacial instability and mixing. Simulations of gas/liquid interface instability show that the influences of initial perturbations on the fluid mixing zone （FMZ） growth are significant, especially at the late stages, while grids have only a slight effect on the FMZ width, when the interface is impulsively accelerated by a shock wave passing through it. A numerical study of the hydrodynamic interfacial instability and mixing of gaseous flows impacted by re-shocks is presented. It reveals that the numerical results are in good agreement with the experimental results and the mixing growth rate strongly depends on initial conditions. Ultimately, the jelly layer experiment relevant to the instability impacted by exploding is simulated. The shape of jelly interface, position of front face of jelly layer, crest and trough of perturbation versus time are given; their simulated results are in good agreement with experimental results.展开更多
Spontaneous rupture of some polymer films upon heating is commonplace. The very criterion for this instability is the system free energy possessing a negative curvature. Within the framework of full frequency-dependen...Spontaneous rupture of some polymer films upon heating is commonplace. The very criterion for this instability is the system free energy possessing a negative curvature. Within the framework of full frequency-dependent theory of dispersion forces, we have derived the excess free energy of a typical system--polystyrene film deposited on the silicon substrate. The excess free energy, wavelengths and growth rates are calculate and a comparison is made between the accurate results and the approximate results. It is found that the stability of the fihn can be tuned by the variation of the thickness of the coating and the retardation effects can be significant sometimes.展开更多
The instability theory of fluid flow is applied in gas atomization and the results show that the instability of interfacial wave is the main cause of gas atomization. The size of the droplets and its change with param...The instability theory of fluid flow is applied in gas atomization and the results show that the instability of interfacial wave is the main cause of gas atomization. The size of the droplets and its change with parameters are also studied, the results are compatible with the experiments.展开更多
A viscous Kelvin-Helmholtz criterion of the interfacial wave instability is proposed in this paper based on the linear stability analysis of a transient one-dimensional two-fluid model. In thismodel, the pressure is e...A viscous Kelvin-Helmholtz criterion of the interfacial wave instability is proposed in this paper based on the linear stability analysis of a transient one-dimensional two-fluid model. In thismodel, the pressure is evaluated using the local momentum balance rather than the hydrostatic approximation. The criterion predicts well the stability limit of stratified flow in horizontal and nearly horizontal pipes. The experimental and theoretical investigation on the effect of pipe inclination on the interfacial instability are carded out. It is found that the critical liquid height at the onset of interfacial wave instability is insensitive to the pipe inclination. However, the pipe inclination significantly affects critical superficial liquid velocity and wave velocity especially lor low gas velocities.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
In this paper,we numerically studied the late-time evolutional mechanism of three-dimensional(3D)single-mode immiscible Rayleigh–Taylor instability(RTI)by using an improved lattice Boltzmann multiphase method impleme...In this paper,we numerically studied the late-time evolutional mechanism of three-dimensional(3D)single-mode immiscible Rayleigh–Taylor instability(RTI)by using an improved lattice Boltzmann multiphase method implemented on graphics processing units.The influences of extensive dimensionless Reynolds numbers and Atwood numbers on phase interfacial dynamics,spike and bubble growth were investigated in details.The longtime numerical experiments indicate that the development of 3D singlemode RTI with a high Reynolds number can be summarized into four different stages:linear growth stage,saturated velocity growth stage,reacceleration stage and turbulent mixing stage.A series of complex interfacial structures with large topological changes can be observed at the turbulent mixing stage,which always preserve the symmetries with respect to the middle axis for a low Atwood number,and the lines of symmetry within spike and bubble are broken as the Atwood number is increased.Five statistical methods for computing the spike and bubble growth rates were then analyzed to reveal the growth law of 3D single-mode RTI in turbulent mixing stage.It is found that the spike late-time growth rate shows an overall increase with the Atwood number,while the bubble growth rate experiences a slight decrease with the Atwood number at first and then basically maintains a steady value of around 0.1.When the Reynolds number decreases,the later stages cannot be reached gradually and the evolution of phase interface presents a laminar flow state.展开更多
The early phases of the shock interaction process on two-dimensional interfaces with different shapes are numerically investigated in this study,which are closely related to the shock refraction and reflection,vortici...The early phases of the shock interaction process on two-dimensional interfaces with different shapes are numerically investigated in this study,which are closely related to the shock refraction and reflection,vorticity production and transport.The numerical method employs an adaptive unstructured quadrilateral mesh,which can capture the wave pattern and interface evolution very well.Simulations are carried out under the conditions of an incident shock Mach number of 1.2 and the light/heavy (air/SF 6) interface.Five different shapes are considered in the simulations:rectangle,ellipse,diamond and two kinds of triangle.The results show that the interfacial shapes can influence the wave patterns particularly on the shape and evolution of refracted shock waves.The generation and the distribution of vorticity on the interfaces with five different shapes also have dissimilarities.The circulation deposition on five interfaces is quantitatively investigated and compared with theoretical model.A good agreement is found between the numerical results and the predictions by the theoretical model.Some characteristic scales of the interface are tracked.Under the influence of nonlinear-acoustic effect and vorticity effect,the interfaces present different evolution modes.展开更多
基金the National Natural Science Foundation of China(No.11971411)the Research Foundation of Education Bureau of Hunan Province of China(No.18A067)。
文摘This study is to numerically test the interfacial instability of ferrofluid flow under the presence of a vacuum magnetic field.The ferrofluid parabolized stability equations(PSEs)are derived from the ferrofluid stability equations and the Rosensweig equations,and the characteristic values of the ferrofluid PSEs are given to describe the ellipticity of ferrofluid flow.Three numerical models representing specific cases considering with/without a vacuum magnetic field or viscosity are created to mathematically examine the interfacial instability by the computation of characteristic values.Numerical investigation shows strong dependence of the basic characteristic of ferrofluid Rayleigh-Taylor instability(RTI)on viscosity of ferrofluid and independence of the vacuum magnetic field.For the shock wave striking helium bubble,the magnetic field is not able to trigger the symmetry breaking of bubble but change the speed of the bubble movement.In the process of droplet formation from a submerged orifice,the collision between the droplet and the liquid surface causes symmetry breaking.Both the viscosity and the magnetic field exacerbate symmetry breaking.The computational results agree with the published experimental results.
文摘The classical linear instability theory was applied to the planar stratified two_layers flow with high speed compressible gas layer impacting on incompressible viscous liquid layer. The walls were kept at different temperatures, resulting in heat transfer across the layers. The thermal conductivity and the density of the gas were alerted when the temperature changes.After some treatment, a four_order stiff ordinary differential equation was derived,and numerical integration and multi_shooting method were used to solve this equation for its spatial mode calculation. The numerical results of characteristic parameters show good coincidence with other models. At the same time, when the wall temperature ratio decreases,as well as the Reynolds number and the gas thermal conductivity change increases, the atomization would be more efficient and producing finer droplets. And the results show good fit with the experimental datum of HJE. Co. Inc (Glens Falls, NY, USA).
基金support of Natural Science and Engineering Research Council of Canada(NSERCRGPIN204992).
文摘Inspired by recent research interest in the interface wrinkling of bonded materials in diverse areas of 3D printing,the present work studies the interfacial instability of two bonded elastic bodies driven by negative interfacial tension or compressible bulk residual stress.For interfacial instability modes decaying exponentially with distance from the interface,the present model is formulated for two bonded elastic half-spaces with a planar interface under plane strain.An explicit expression is given for the wavenumber of interfacial instability driven by negative interfacial tension,and a critical condition is derived for interfacial instability driven by compressive bulk residual stress.The derived results are validated with comparison to known results on surface instability of an elastic half-space,and the role of shear modulus ratio and Poisson’s ratios of two bonded elastic bodies in interfacial instability,an issue to be addressed in literature,is studied with specific reference to material parameters used in some areas of 3D printing.
文摘The problem of nonlinear instability of interfacial waves between two immiscible conducting cylindrical fluids of a weak Oldroyd 3-constant kind is studied. The system is assumed to be influenced by an axial magnetic field, where the effect of surface tension is taken into account. The analysis, based on the method of multiple scale in both space and time, includes the linear as well as the nonlinear effects. This scheme leads to imposing of two levels of the solvability conditions, which are used to construct like-nonlinear Schr6dinger equations （1-NLS） with complex coefficients. These equations generally describe the competition between nonlinearity and dispersion. The stability criteria are theoret- ically discussed and thereby stability diagrams are obtained for different sets of physical parameters. Proceeding to the nonlinear step of the problem, the results show the appearance of dual role of some physical parameters. Moreover, these effects depend on the wave kind, short or long, except for the ordinary viscosity parameter. The effect of the field on the system stability depends on the existence of viscosity and differs in the linear case of the problem from the nonlinear one. There is an obvious difference between the effect of the three Oldroyd constants on the system stability. New instability regions in the parameter space, which appear due to nonlinear effects, are shown.
基金supported by the National Natural Science Foundation of China(Grant Nos.U23B6009 and 12272050).
文摘This review summarizes recent progress in the study of impinging-jet dynamics and atomization,with a focus on liquid sheet formation,instability mechanisms,and the influence of key parameters such as fluid properties,Weber number,and Reynolds number.Special attention is given to atomization behaviors under high pressure and external perturbations.Representative experimental and numerical approaches are introduced,and critical findings under complex conditions are highlighted.In addition,practical applications of impinging-jet technology in aerospace propulsion,biomedical devices,and energy science are discussed.This review aims to serve as a concise reference for researchers interested in multiphase flow dynamics and engineering applications of impinging jets.
基金supported by the National Natural Science Foundation of China (Grant Nos 10672151 and 10772166)the Foundation of China Academy of Engineering Physics (Grant No 2008B0202011)the Fundamental Quality and Reliability of National Defence Science and Technology Industry of China
文摘Based on multi-fluid volume fraction and piecewise parabolic method （PPM）, a multi-viscosity-fluid hydrodynamic code MVPPM （Multi-Viscosity-Fluid Piecewise Parabolic Method） is developed and applied to the problems of shock-induced hydrodynamic interfacial instability and mixing. Simulations of gas/liquid interface instability show that the influences of initial perturbations on the fluid mixing zone （FMZ） growth are significant, especially at the late stages, while grids have only a slight effect on the FMZ width, when the interface is impulsively accelerated by a shock wave passing through it. A numerical study of the hydrodynamic interfacial instability and mixing of gaseous flows impacted by re-shocks is presented. It reveals that the numerical results are in good agreement with the experimental results and the mixing growth rate strongly depends on initial conditions. Ultimately, the jelly layer experiment relevant to the instability impacted by exploding is simulated. The shape of jelly interface, position of front face of jelly layer, crest and trough of perturbation versus time are given; their simulated results are in good agreement with experimental results.
基金Project supported by the Natural Science Foundation of Hu＇nan Province, China （Grant No 00JJY2072）, and the Foundation of Educational Committee of Hu＇nan Province, China （Grant Nos 00C189 and 01B019）.
文摘Spontaneous rupture of some polymer films upon heating is commonplace. The very criterion for this instability is the system free energy possessing a negative curvature. Within the framework of full frequency-dependent theory of dispersion forces, we have derived the excess free energy of a typical system--polystyrene film deposited on the silicon substrate. The excess free energy, wavelengths and growth rates are calculate and a comparison is made between the accurate results and the approximate results. It is found that the stability of the fihn can be tuned by the variation of the thickness of the coating and the retardation effects can be significant sometimes.
文摘The instability theory of fluid flow is applied in gas atomization and the results show that the instability of interfacial wave is the main cause of gas atomization. The size of the droplets and its change with parameters are also studied, the results are compatible with the experiments.
基金Supported by the National Natural Science Foundation of China （No.50521604） and Shanghai Jiao Tong University Young Teacher Foundation.
文摘A viscous Kelvin-Helmholtz criterion of the interfacial wave instability is proposed in this paper based on the linear stability analysis of a transient one-dimensional two-fluid model. In thismodel, the pressure is evaluated using the local momentum balance rather than the hydrostatic approximation. The criterion predicts well the stability limit of stratified flow in horizontal and nearly horizontal pipes. The experimental and theoretical investigation on the effect of pipe inclination on the interfacial instability are carded out. It is found that the critical liquid height at the onset of interfacial wave instability is insensitive to the pipe inclination. However, the pipe inclination significantly affects critical superficial liquid velocity and wave velocity especially lor low gas velocities.
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This work was financially supported by the National Natural Science Foundation of China(Grant Nos.11972142 and 51976128)。
文摘In this paper,we numerically studied the late-time evolutional mechanism of three-dimensional(3D)single-mode immiscible Rayleigh–Taylor instability(RTI)by using an improved lattice Boltzmann multiphase method implemented on graphics processing units.The influences of extensive dimensionless Reynolds numbers and Atwood numbers on phase interfacial dynamics,spike and bubble growth were investigated in details.The longtime numerical experiments indicate that the development of 3D singlemode RTI with a high Reynolds number can be summarized into four different stages:linear growth stage,saturated velocity growth stage,reacceleration stage and turbulent mixing stage.A series of complex interfacial structures with large topological changes can be observed at the turbulent mixing stage,which always preserve the symmetries with respect to the middle axis for a low Atwood number,and the lines of symmetry within spike and bubble are broken as the Atwood number is increased.Five statistical methods for computing the spike and bubble growth rates were then analyzed to reveal the growth law of 3D single-mode RTI in turbulent mixing stage.It is found that the spike late-time growth rate shows an overall increase with the Atwood number,while the bubble growth rate experiences a slight decrease with the Atwood number at first and then basically maintains a steady value of around 0.1.When the Reynolds number decreases,the later stages cannot be reached gradually and the evolution of phase interface presents a laminar flow state.
基金supported by the National Natural Science Foundation of China (Grant No.10972214)the Fundamental Research Funds for the Central Universities
文摘The early phases of the shock interaction process on two-dimensional interfaces with different shapes are numerically investigated in this study,which are closely related to the shock refraction and reflection,vorticity production and transport.The numerical method employs an adaptive unstructured quadrilateral mesh,which can capture the wave pattern and interface evolution very well.Simulations are carried out under the conditions of an incident shock Mach number of 1.2 and the light/heavy (air/SF 6) interface.Five different shapes are considered in the simulations:rectangle,ellipse,diamond and two kinds of triangle.The results show that the interfacial shapes can influence the wave patterns particularly on the shape and evolution of refracted shock waves.The generation and the distribution of vorticity on the interfaces with five different shapes also have dissimilarities.The circulation deposition on five interfaces is quantitatively investigated and compared with theoretical model.A good agreement is found between the numerical results and the predictions by the theoretical model.Some characteristic scales of the interface are tracked.Under the influence of nonlinear-acoustic effect and vorticity effect,the interfaces present different evolution modes.
