Liquid sloshing is a kind of very complicated free surface flow and exists widely in many fields.In order to calculate liquid sloshing damping precisely a volume of fluid method based on finite volume scheme is used t...Liquid sloshing is a kind of very complicated free surface flow and exists widely in many fields.In order to calculate liquid sloshing damping precisely a volume of fluid method based on finite volume scheme is used to simulate free surface flows in partly filled cylindrical containers.A numerical method is pre-sented to simulate the movement of the free surface flow,in which a piecewise linear interface con-struction scheme and an unsplit Lagrangian advection scheme instead of Eulerian advection scheme are used.The damping performance of liquid sloshing in cylindrical containers under fundamental sloshing mode is investigated.There are four factors determining the surface-wave damping:free surface,boundary-layer,interior fluid and contact line.In order to study different contributions from these four factors to whole damping,several examples are simulated.No-slip and slip wall boundary conditions on both side wall and bottom wall of the cylindrical containers are studied to compare with the published results obtained by solving Stokes equations.In the present method the first three main factors can be considered.The simulation results show that the boundary-layer damping contribution increases while the interior fluid damping contribution decreases with increase of Reynolds number.展开更多
In the present study, a new algorithm based on the Volume Of Fluid （VOF） method is developed to simulate the hydrodynamic characteristics on an arc crown wall. Structured grids are generated by the coordinate transf...In the present study, a new algorithm based on the Volume Of Fluid （VOF） method is developed to simulate the hydrodynamic characteristics on an arc crown wall. Structured grids are generated by the coordinate transform method in an arbitrary complex region. The Navier-Stokes equations for two-dimensional incompressible viscous flows are discretized in the Body Fitted Coordinate （BFC） system. The transformed SIMPLE algorithm is proposed to modify the pressure-velocity field and a transformed VOF method is used to trace the free surface. Hydrodynamic characteristics on an arc crown wall are obtained by the improved numerical model based on the BFC system （BFC model）. The velocity field, the pressure field and the time profiles of the water surface near the arc crown wall obtained by using the BFC model and the Cartesian model are compared. The BFC model is verified by experimental results.展开更多
An Unsplit Lagrangian Advection （ULA） scheme for Volume Of Fluid （VOF） method is presented in this article. The ULA scheme is developed based on an algorithm of Piecewise Linear Interface Construction （PLIC）. Th...An Unsplit Lagrangian Advection （ULA） scheme for Volume Of Fluid （VOF） method is presented in this article. The ULA scheme is developed based on an algorithm of Piecewise Linear Interface Construction （PLIC）. The volume fluxes between cells are calculated through solving the new equation of the linear interfaces in cells in the ULA scheme. The fluxes flowing out from one cell is the inflow fluxes for another cell. In this way the whole fluid volume is conserved strictly without using any redistribution algorithms. The ULA scheme is based on two-dimensional structured rectangular mesh and may be extended to three-dimensional structured mesh with more geometrical efforts. The results from three widely-used benchmark tests show that the ULA scheme can achieve the accuracy higher than Split Lagaragian Advection （SLA） scheme and the Flux-Corrected Transport （FCT） algorithm.展开更多
The coupled level-set and volume of fluid(CLSVOF)method is an advanced interface-capturing method that has been extended to handle overset grid systems.However,artificial uneven interface may be observed across block ...The coupled level-set and volume of fluid(CLSVOF)method is an advanced interface-capturing method that has been extended to handle overset grid systems.However,artificial uneven interface may be observed across block boundaries of different sizes and geometries.We present an improved inter-grid VOF interpolation and mass correction scheme to address the issue.To demonstrate the capability of the improved CLSVOF method,it is applied to the simulation of a container ship in pitch and heave motions under both head sea and following sea irregular wave conditions.Our simulation proves that the improved CLSVOF method is capable of revealing detailed physics difficult to see with other methods.Those phenomena simulated in our work include the extensive greenwater propagation on the ship deck,the breakup of overtopping waves into small droplets,and the formation and collapse of air pockets in sudden bow and stern slamming which cause strong and highly localized impacts on the ship bow,stern,and rudder.展开更多
A stencil-like volume of fluid （VOF） method is proposed for tracking free interface. A stencil on a grid cell is worked out according to the normal direction of the interface, in which only three interface positions...A stencil-like volume of fluid （VOF） method is proposed for tracking free interface. A stencil on a grid cell is worked out according to the normal direction of the interface, in which only three interface positions are possible in 2D cases, and the interface can be reconstructed by only requiring the known local volume fraction information. On the other hand, the fluid-occupying-length is defined on each side of the stencil, through which a unified fluid-occupying volume model and a unified algorithm can be obtained to solve the interface advection equation. The method is suitable for the arbitrary geometry of the grid cell, and is extendible to 3D cases. Typical numerical examples show that the current method can give ＂sharp＂ results for tracking free interface.展开更多
The present study provides a three-dimensional volume-of-fluid method based on the adaptive mesh refinement technique.The projection method on the adaptive mesh is introduced for solving the incompressible Navier-Stok...The present study provides a three-dimensional volume-of-fluid method based on the adaptive mesh refinement technique.The projection method on the adaptive mesh is introduced for solving the incompressible Navier-Stokes equations.The octree structure mesh is employed to solve the flow velocities and the pressure.The developed solver is applied to simulate the deformation of the cubic droplet driven by the surface tension without the effect of the gravity.The numerical results well predict the shape evolution of the droplet.展开更多
The unstable fluid flow and severe free surface fluctuations in the wheel and belt caster can affect the quality of the cast bar.The lower level height tends to entrap inclusions in the molten metal.On the other hand,...The unstable fluid flow and severe free surface fluctuations in the wheel and belt caster can affect the quality of the cast bar.The lower level height tends to entrap inclusions in the molten metal.On the other hand,the higher level height makes the production process more dangerous due to the overflow of high temperature fluid from the mold.A computational model of the molten metal pouring process was established.The transient fluid flow and free surface fluctuations behavior were calculated using the three-dimensional large eddy simulation model and the volume of fluid model.The results show that the flow velocity of the main jet gradually decreases under the influence of the low kinetic energy fluid in the mold.There is an obvious oscillation in the tail of the jet,while the flow field is asymmetric in space.The jet is closer to the inside radius side due to the Coanda effect,and there is a recirculation zone on the inside radius and the outside radius respectively,according to the 10 s time-averaged results.Compared with the industrial observation and simulation results,the shape of the free surface is a wave that varies with time.In addition,the free surface height is lowest and the flow velocity is highest in the region near the jet.展开更多
Cold air is one key factor affecting the freezing process of ice tanks.The volume of fluid method is employed to simulate the freezing process of water in an ice tank with cold air inlets.The temperature field distrib...Cold air is one key factor affecting the freezing process of ice tanks.The volume of fluid method is employed to simulate the freezing process of water in an ice tank with cold air inlets.The temperature field distribution in the ice tank is calculated.The temperature field at different typical instants are compared.The main characteristics of the freezing process in an ice tank driven by cold air are analyzed.The influence of the number of cold air inlets on the freezing process is investigated.The numerical results show that with increasing the number of cold air inlets,the temperature field becomes more uniform.The inlet velocity of cold air has a great influence on the generation of ice.This work can serve for the design of the ice tank and control of the freezing process.展开更多
Sloshing is a common phenomenon in nature and industry, and it is important in many fields, such as marine engineering and aerospace engineering. To reduce the sloshing load on the side walls, the topology optimizatio...Sloshing is a common phenomenon in nature and industry, and it is important in many fields, such as marine engineering and aerospace engineering. To reduce the sloshing load on the side walls, the topology optimization and optimal control methods are used to design the shape of the board, which is fixed in the middle of the tank. The results show that the new board shape, which is designed via topology optimization, can significantly reduce the sloshing load on the side wall.展开更多
An unsteady load calculation method for the support configuration of a monopile-supported offshore wind turbine is developed based on the Fluent software platform.Firstly,the water wave is generated by imposing the in...An unsteady load calculation method for the support configuration of a monopile-supported offshore wind turbine is developed based on the Fluent software platform.Firstly,the water wave is generated by imposing the inlet boundary conditions according to the exact potential flow solution.Then the wave evolution is simulated by solving the unsteady incompressible Navier-Stokes(N-S)equations coupled with the volume of fluid method.For the small amplitude wave with reasonable wave parameters,the numerical wave result agrees well with that of the given wave model.Finally,a monopile support configuration is introduced and a CFD-based load calculation method is established to accurately calculate the unsteady load under the combined action of wave and wind.The computed unsteady wave load on a small-size monopile support located in the small amplitude wave flow coincides with that of the Morison formula.The load calculations are also performed on a large-size monopile support and a monopile-supported offshore wind turbine under the combined action of small amplitude wave and wind.展开更多
The icing of areo-engine inlet components during flight can affect engine operational safety.Conventional hot-air anti-icing systems require a large amount of bleed air,which compromises engine performance.Consequentl...The icing of areo-engine inlet components during flight can affect engine operational safety.Conventional hot-air anti-icing systems require a large amount of bleed air,which compromises engine performance.Consequently,low-energy anti/de-icing methods based on superhydrophobic surfaces have attracted widespread attention.Previous studies have demonstrated that for stationary components,superhydrophobic surfaces can significantly reduce anti-icing energy consumption by altering the flow behavior of runback water.However,for rotating inlet components of aero-engines,the effectiveness of superhydrophobic surfaces and the influence of surface wettability on the evolution of runback water flow remain unclear due to the effects of centrifugal and Coriolis forces.This study establishes a 3D liquid water flow simulation model using the volume of fluid(VOF)method to investigate the effects of rotational speed,airflow velocity,and surface wettability on the runback water flow behavior over the rotating spinner under dynamic rotation conditions.The results show that the rotational effects and surface wettability mutually reinforce one another.Specifically,increasing the rotational speed and contact angle can both enhance the flow velocity of liquid water and accelerate the breakup and rupture of liquid film,leading to the formation of rivulets,droplets,and subsequent detachment from the surface.A theoretical model based on force balance is proposed to describe the evolution of runback water flow,and the analysis reveals that as the rotational speed and contact angle increase,the water film is more likely to break up to form rivulets and beads,and the critical radius for droplet detachment from the surface decreases,making it easier removal from the surface.展开更多
This paper introduces a numerical model for studying the evolution of a periodic wave train, shoaling, and breaking in surf zone. The model can solve the Reynolds averaged Navier-Stokes （RANS） equations for a mean f...This paper introduces a numerical model for studying the evolution of a periodic wave train, shoaling, and breaking in surf zone. The model can solve the Reynolds averaged Navier-Stokes （RANS） equations for a mean flow, and the k-ε equations for turbulence kinetic energy k and turbulence dissipation rate ε. To track a free surface, the volume of fluid （VOF） function, satisfying the advection equation was introduced. In the numerical treatment, third-order upwind difference scheme was applied to the convection terms of the RANS equations in order to reduce the effect of numerical viscosity. The shoaling and breaking processes of a periodic wave train on gently sloping beaches were modeled. The computed wave heights of a sloping beach and the distribution of breaking wave pressure on a vertical wall were compared with laboratory data.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
In the present research,two numerical schemes for improving the accuracy of the solution in the flow simulation of molten metal were applied.One method is the Piecewise Linear Interface Calculation(PLIC) method and th...In the present research,two numerical schemes for improving the accuracy of the solution in the flow simulation of molten metal were applied.One method is the Piecewise Linear Interface Calculation(PLIC) method and the other is the Donor-Acceptor(D-A) method.To verify the module of the interface reconstruction algorithms,simple problems were tested.After these validations,the accuracy and efficiency of these two methods were compared by simulating various real products.On the numerical simulation of free surface flow,it is possible for the PLIC method to track very accurately the interface between phases.The PLIC method,however,has the weak point in that a lot of computational time is required,though it shows the more accurate interface reconstruction.The Donor-Acceptor method has enough effectiveness in the macro-observation of a mold filling sequence though it shows inferior accuracy.Therefore,for the problems that need the accurate solution,PLIC is more appropriate than D-A.More accuracy may cause less efficiency in numerical analysis.Which method between D-A method and PLIC method should be chosen depends on the product.展开更多
The interaction between regular water waves and a submerged obstacle in a channel is studied numerically. The fluid viscosity is taken into account and the volume of fluid method is used to deal with the free surface...The interaction between regular water waves and a submerged obstacle in a channel is studied numerically. The fluid viscosity is taken into account and the volume of fluid method is used to deal with the free surface. The incident regular waves are generated by use of numerical absorbing wave maker paddle. The present method can be used to predict the nonlinear deformations of the transmitted regular waves, and to simulate the vortex flow near the obstacle and the shear flows beneath the free surface.展开更多
The asymmetric breakups of a droplet in an axisymmetric cross-like microfluidic device are investigated by using a three-dimensional volume of fluid(VOF) multiphase numerical model. Two kinds of asymmetries(droplet lo...The asymmetric breakups of a droplet in an axisymmetric cross-like microfluidic device are investigated by using a three-dimensional volume of fluid(VOF) multiphase numerical model. Two kinds of asymmetries(droplet location deviation from the symmetric geometry center and different flow rates at two symmetric outlets) generate asymmetric flow fields near the droplet, which results in the asymmetric breakup of the latter. Four typical breakup regimes(no breakup, one-side breakup, retraction breakup and direct breakup) have been observed.Two regime maps are plotted to describe the transition from one regime to another for the two types of different asymmetries, respectively. A power law model, which is based on the three critical factors(the capillary number,the asymmetry of flow fields and the initial volume ratio), is employed to predict the volume ratio of the two unequal daughter droplets generated in the direct breakup. The influences of capillary numbers and the asymmetries have been studied systematically in this paper. The larger the asymmetry is, the bigger the oneside breakup zone is. The larger the capillary number is, the more possible the breakup is in the direct breakup zone. When the radius of the initial droplet is 20 μm, the critical capillary numbers are 0.122, 0.128, 0.145,0.165, 0.192 and 0.226 for flow asymmetry factor AS= 0.05, 0.1, 0.2, 0.3, 0.4 and 0.5, respectively, in the flow system whose asymmetry is generated by location deviations. In the flow system whose asymmetry is generated by two different flow rates at two outlets, the critical capillary numbers are 0.121, 0.133, 0.145, 0.156 and 0.167 for AS= 1/21, 3/23, 1/5, 7/27 and 9/29, respectively.展开更多
The influence of baffle position on liquid sloshing during the braking and turning of a tank truck was studied using a volume of fluid (VOF) model. The forces,their positions and weight distribution during braking and...The influence of baffle position on liquid sloshing during the braking and turning of a tank truck was studied using a volume of fluid (VOF) model. The forces,their positions and weight distribution during braking and the forces and rolling moment during turning were calculated. The reliability of the calculation method was validated by comparisons with experimental results. The results showed that during braking,liquid splashes in the tank and the maximum forces and G (the ratio of weight acting on the front axle to the rear axle) are large when A (the ratio of the arch area above the baffle to the area of cross section)≤0.1. When A≥0.2,as the position of the baffle is lowered,the maximum of Fx (the force in direction x) first decreases then increases,and the maximum of Fy (the force in direction y) and G increase. During turning,liquid splashes in the tank and the maximum forces and M (the rolling moment) are large when D (the ratio of the arch area above the baffle to the area of cross section)≤0.2. When D≥0.3,as the position of the baffle is lowered,the maximums of Fy,Fz (the force in direction z) and M increase.展开更多
Numerous gas-liquid-solid flows exist in chemical engineering and metallurgical processes. Numerical modeling is an important topic that can be used to improve the design and investigate the operating conditions of th...Numerous gas-liquid-solid flows exist in chemical engineering and metallurgical processes. Numerical modeling is an important topic that can be used to improve the design and investigate the operating conditions of these processes. The complicated interphase interaction within such three-phase systems, which include free surfaces and discrete phases, poses challenges in the existing methods. We imple- mented a volume-of-fluid （VOF） and discrete-element-method （DEM） combined solver, which should be useful for modeling the gas-liquid-solid systems, within the OpenFOAM framework. The Du Plessis and Masliyah drag force, added mass force, and capillary force were considered for fluid-particle coupling. The VOF-DEM solver was tested in three different cases, namely, particles in pure gas, particle collision in water, and gas-liquid-solid three-phase dam break. The results were validated against previous experi- ments and good agreement was obtained between the simulations and the experiments, which indicates the accuracy and suitability of this VOF-DEM solver for gas-liquid-solid systems.展开更多
Partial coalescence is a complicated flow phenomenon.In the present study,the coalescence process is simulated with the volume of fluid(VOF)method.The numerical results reveal that a downward high-velocity region play...Partial coalescence is a complicated flow phenomenon.In the present study,the coalescence process is simulated with the volume of fluid(VOF)method.The numerical results reveal that a downward high-velocity region plays a significant role in partial coalescence.The high-velocity region pulls the droplet downward continuously which is an important factor for the droplet turning into a prolate shape and the final pinch-off.The shift from partial coalescence to full coalescence is explained based on the droplet shape before the pinch-off.With the droplet impact velocity increasing,the droplet shape will get close to a sphere before the pinch-off.When the shape gets close enough to a sphere,the partial coalescence shifts to full coalescence.The effect of film thickness on the coalescence process is also investigated.With large film thickness,partial coalescence happens,while with small film thickness,full coalescence happens.In addition,the results indicate that the critical droplet impact velocity increases with the increase of surface tension coefficient but decreases with the increase of viscosity and initial droplet diameter.And there is a maximum critical Weber number with the increase of surface tension coefficient and initial droplet diameter.展开更多
In the inviscid and incompressible fluid flow regime,surface tension effects on the behaviour of an initially spherical buoyancy-driven bubble rising in an infinite and initially stationary liquid are investigated num...In the inviscid and incompressible fluid flow regime,surface tension effects on the behaviour of an initially spherical buoyancy-driven bubble rising in an infinite and initially stationary liquid are investigated numerically by a volume of fluid （VOF） method. The ratio of the gas density to the liquid density is 0.001, which is close to the case of an air bubble rising in water. It is found by numerical experiment that there exist four critical Weber numbers We1,~We2,~We3 and We4, which distinguish five different kinds of bubble behaviours. It is also found that when 1≤We2, the bubble will finally reach a steady shape, and in this case after it rises acceleratedly for a moment, it will rise with an almost constant speed, and the lower the Weber number is, the higher the speed is. When We 〉We2, the bubble will not reach a steady shape, and in this case it will not rise with a constant speed. The mechanism of the above phenomena has been analysed theoretically and numerically.展开更多
基金Supported by the National Natural Science Foundation of China(Grant No.10532010)
文摘Liquid sloshing is a kind of very complicated free surface flow and exists widely in many fields.In order to calculate liquid sloshing damping precisely a volume of fluid method based on finite volume scheme is used to simulate free surface flows in partly filled cylindrical containers.A numerical method is pre-sented to simulate the movement of the free surface flow,in which a piecewise linear interface con-struction scheme and an unsplit Lagrangian advection scheme instead of Eulerian advection scheme are used.The damping performance of liquid sloshing in cylindrical containers under fundamental sloshing mode is investigated.There are four factors determining the surface-wave damping:free surface,boundary-layer,interior fluid and contact line.In order to study different contributions from these four factors to whole damping,several examples are simulated.No-slip and slip wall boundary conditions on both side wall and bottom wall of the cylindrical containers are studied to compare with the published results obtained by solving Stokes equations.In the present method the first three main factors can be considered.The simulation results show that the boundary-layer damping contribution increases while the interior fluid damping contribution decreases with increase of Reynolds number.
基金supported by the National Natural Science Foundation of China (Grant Nos. 51179030, 50921001)
文摘In the present study, a new algorithm based on the Volume Of Fluid （VOF） method is developed to simulate the hydrodynamic characteristics on an arc crown wall. Structured grids are generated by the coordinate transform method in an arbitrary complex region. The Navier-Stokes equations for two-dimensional incompressible viscous flows are discretized in the Body Fitted Coordinate （BFC） system. The transformed SIMPLE algorithm is proposed to modify the pressure-velocity field and a transformed VOF method is used to trace the free surface. Hydrodynamic characteristics on an arc crown wall are obtained by the improved numerical model based on the BFC system （BFC model）. The velocity field, the pressure field and the time profiles of the water surface near the arc crown wall obtained by using the BFC model and the Cartesian model are compared. The BFC model is verified by experimental results.
基金supported by the National Natural Science Foundarion of China (Grant No.10532010)
文摘An Unsplit Lagrangian Advection （ULA） scheme for Volume Of Fluid （VOF） method is presented in this article. The ULA scheme is developed based on an algorithm of Piecewise Linear Interface Construction （PLIC）. The volume fluxes between cells are calculated through solving the new equation of the linear interfaces in cells in the ULA scheme. The fluxes flowing out from one cell is the inflow fluxes for another cell. In this way the whole fluid volume is conserved strictly without using any redistribution algorithms. The ULA scheme is based on two-dimensional structured rectangular mesh and may be extended to three-dimensional structured mesh with more geometrical efforts. The results from three widely-used benchmark tests show that the ULA scheme can achieve the accuracy higher than Split Lagaragian Advection （SLA） scheme and the Flux-Corrected Transport （FCT） algorithm.
基金This work was supported by the Ocean Systems Simulation and Control Laboratory(OSSCL)Consortium.
文摘The coupled level-set and volume of fluid(CLSVOF)method is an advanced interface-capturing method that has been extended to handle overset grid systems.However,artificial uneven interface may be observed across block boundaries of different sizes and geometries.We present an improved inter-grid VOF interpolation and mass correction scheme to address the issue.To demonstrate the capability of the improved CLSVOF method,it is applied to the simulation of a container ship in pitch and heave motions under both head sea and following sea irregular wave conditions.Our simulation proves that the improved CLSVOF method is capable of revealing detailed physics difficult to see with other methods.Those phenomena simulated in our work include the extensive greenwater propagation on the ship deck,the breakup of overtopping waves into small droplets,and the formation and collapse of air pockets in sudden bow and stern slamming which cause strong and highly localized impacts on the ship bow,stern,and rudder.
基金Project supported by the National Natural Science Foundation of China (No.10672097)Shanghai Leading Academic Discipline Project (No.Y0103)
文摘A stencil-like volume of fluid （VOF） method is proposed for tracking free interface. A stencil on a grid cell is worked out according to the normal direction of the interface, in which only three interface positions are possible in 2D cases, and the interface can be reconstructed by only requiring the known local volume fraction information. On the other hand, the fluid-occupying-length is defined on each side of the stencil, through which a unified fluid-occupying volume model and a unified algorithm can be obtained to solve the interface advection equation. The method is suitable for the arbitrary geometry of the grid cell, and is extendible to 3D cases. Typical numerical examples show that the current method can give ＂sharp＂ results for tracking free interface.
基金This work was supported by the National Natural Science Foun-dation of China(No.41776194).
文摘The present study provides a three-dimensional volume-of-fluid method based on the adaptive mesh refinement technique.The projection method on the adaptive mesh is introduced for solving the incompressible Navier-Stokes equations.The octree structure mesh is employed to solve the flow velocities and the pressure.The developed solver is applied to simulate the deformation of the cubic droplet driven by the surface tension without the effect of the gravity.The numerical results well predict the shape evolution of the droplet.
基金supported by Innovative Research Groups Project of the Natural Science Foundation of Hebei Province(No.E2021203011)Central Government Guides Local Science and Technology Development Fund Projects(No.206Z1601G).
文摘The unstable fluid flow and severe free surface fluctuations in the wheel and belt caster can affect the quality of the cast bar.The lower level height tends to entrap inclusions in the molten metal.On the other hand,the higher level height makes the production process more dangerous due to the overflow of high temperature fluid from the mold.A computational model of the molten metal pouring process was established.The transient fluid flow and free surface fluctuations behavior were calculated using the three-dimensional large eddy simulation model and the volume of fluid model.The results show that the flow velocity of the main jet gradually decreases under the influence of the low kinetic energy fluid in the mold.There is an obvious oscillation in the tail of the jet,while the flow field is asymmetric in space.The jet is closer to the inside radius side due to the Coanda effect,and there is a recirculation zone on the inside radius and the outside radius respectively,according to the 10 s time-averaged results.Compared with the industrial observation and simulation results,the shape of the free surface is a wave that varies with time.In addition,the free surface height is lowest and the flow velocity is highest in the region near the jet.
基金the Key Technologies Research and Development Program(No.2022YFE0107000)the National Natural Science Foundation of China(No.52171259)。
文摘Cold air is one key factor affecting the freezing process of ice tanks.The volume of fluid method is employed to simulate the freezing process of water in an ice tank with cold air inlets.The temperature field distribution in the ice tank is calculated.The temperature field at different typical instants are compared.The main characteristics of the freezing process in an ice tank driven by cold air are analyzed.The influence of the number of cold air inlets on the freezing process is investigated.The numerical results show that with increasing the number of cold air inlets,the temperature field becomes more uniform.The inlet velocity of cold air has a great influence on the generation of ice.This work can serve for the design of the ice tank and control of the freezing process.
基金Project supported by the National Natural Science Foundation of China(Nos.11572350,11372068,and 11602051)the National Key Basic Research and Development Program of China(No.2014CB744104)
文摘Sloshing is a common phenomenon in nature and industry, and it is important in many fields, such as marine engineering and aerospace engineering. To reduce the sloshing load on the side walls, the topology optimization and optimal control methods are used to design the shape of the board, which is fixed in the middle of the tank. The results show that the new board shape, which is designed via topology optimization, can significantly reduce the sloshing load on the side wall.
基金supported partly by the National Basic Research Program of China("973"Program)(No.2014CB046200)the National Natural Science Foundation of China(No.11372135)the NUAA Fundamental Research Funds(No.NS2013005)
文摘An unsteady load calculation method for the support configuration of a monopile-supported offshore wind turbine is developed based on the Fluent software platform.Firstly,the water wave is generated by imposing the inlet boundary conditions according to the exact potential flow solution.Then the wave evolution is simulated by solving the unsteady incompressible Navier-Stokes(N-S)equations coupled with the volume of fluid method.For the small amplitude wave with reasonable wave parameters,the numerical wave result agrees well with that of the given wave model.Finally,a monopile support configuration is introduced and a CFD-based load calculation method is established to accurately calculate the unsteady load under the combined action of wave and wind.The computed unsteady wave load on a small-size monopile support located in the small amplitude wave flow coincides with that of the Morison formula.The load calculations are also performed on a large-size monopile support and a monopile-supported offshore wind turbine under the combined action of small amplitude wave and wind.
基金supported by the National Natural Science Foundation of China(No.12172029)the open Resarch Project of Key Laboratory of Icing and Anti/De-icing of CARDC(No.IADL 20230101)。
文摘The icing of areo-engine inlet components during flight can affect engine operational safety.Conventional hot-air anti-icing systems require a large amount of bleed air,which compromises engine performance.Consequently,low-energy anti/de-icing methods based on superhydrophobic surfaces have attracted widespread attention.Previous studies have demonstrated that for stationary components,superhydrophobic surfaces can significantly reduce anti-icing energy consumption by altering the flow behavior of runback water.However,for rotating inlet components of aero-engines,the effectiveness of superhydrophobic surfaces and the influence of surface wettability on the evolution of runback water flow remain unclear due to the effects of centrifugal and Coriolis forces.This study establishes a 3D liquid water flow simulation model using the volume of fluid(VOF)method to investigate the effects of rotational speed,airflow velocity,and surface wettability on the runback water flow behavior over the rotating spinner under dynamic rotation conditions.The results show that the rotational effects and surface wettability mutually reinforce one another.Specifically,increasing the rotational speed and contact angle can both enhance the flow velocity of liquid water and accelerate the breakup and rupture of liquid film,leading to the formation of rivulets,droplets,and subsequent detachment from the surface.A theoretical model based on force balance is proposed to describe the evolution of runback water flow,and the analysis reveals that as the rotational speed and contact angle increase,the water film is more likely to break up to form rivulets and beads,and the critical radius for droplet detachment from the surface decreases,making it easier removal from the surface.
基金Supported by the High-Tech Research and Development Program of China (863 Program, No. 2001AA633070 2003AA604040)the National Natural Science Foundation of China (No. 40476015).
文摘This paper introduces a numerical model for studying the evolution of a periodic wave train, shoaling, and breaking in surf zone. The model can solve the Reynolds averaged Navier-Stokes （RANS） equations for a mean flow, and the k-ε equations for turbulence kinetic energy k and turbulence dissipation rate ε. To track a free surface, the volume of fluid （VOF） function, satisfying the advection equation was introduced. In the numerical treatment, third-order upwind difference scheme was applied to the convection terms of the RANS equations in order to reduce the effect of numerical viscosity. The shoaling and breaking processes of a periodic wave train on gently sloping beaches were modeled. The computed wave heights of a sloping beach and the distribution of breaking wave pressure on a vertical wall were compared with laboratory data.
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In the present research,two numerical schemes for improving the accuracy of the solution in the flow simulation of molten metal were applied.One method is the Piecewise Linear Interface Calculation(PLIC) method and the other is the Donor-Acceptor(D-A) method.To verify the module of the interface reconstruction algorithms,simple problems were tested.After these validations,the accuracy and efficiency of these two methods were compared by simulating various real products.On the numerical simulation of free surface flow,it is possible for the PLIC method to track very accurately the interface between phases.The PLIC method,however,has the weak point in that a lot of computational time is required,though it shows the more accurate interface reconstruction.The Donor-Acceptor method has enough effectiveness in the macro-observation of a mold filling sequence though it shows inferior accuracy.Therefore,for the problems that need the accurate solution,PLIC is more appropriate than D-A.More accuracy may cause less efficiency in numerical analysis.Which method between D-A method and PLIC method should be chosen depends on the product.
文摘The interaction between regular water waves and a submerged obstacle in a channel is studied numerically. The fluid viscosity is taken into account and the volume of fluid method is used to deal with the free surface. The incident regular waves are generated by use of numerical absorbing wave maker paddle. The present method can be used to predict the nonlinear deformations of the transmitted regular waves, and to simulate the vortex flow near the obstacle and the shear flows beneath the free surface.
基金Supported by Major State Basic Research Development Program of China(2012CB720305)the National Natural Science Foundation of China(21376162)
文摘The asymmetric breakups of a droplet in an axisymmetric cross-like microfluidic device are investigated by using a three-dimensional volume of fluid(VOF) multiphase numerical model. Two kinds of asymmetries(droplet location deviation from the symmetric geometry center and different flow rates at two symmetric outlets) generate asymmetric flow fields near the droplet, which results in the asymmetric breakup of the latter. Four typical breakup regimes(no breakup, one-side breakup, retraction breakup and direct breakup) have been observed.Two regime maps are plotted to describe the transition from one regime to another for the two types of different asymmetries, respectively. A power law model, which is based on the three critical factors(the capillary number,the asymmetry of flow fields and the initial volume ratio), is employed to predict the volume ratio of the two unequal daughter droplets generated in the direct breakup. The influences of capillary numbers and the asymmetries have been studied systematically in this paper. The larger the asymmetry is, the bigger the oneside breakup zone is. The larger the capillary number is, the more possible the breakup is in the direct breakup zone. When the radius of the initial droplet is 20 μm, the critical capillary numbers are 0.122, 0.128, 0.145,0.165, 0.192 and 0.226 for flow asymmetry factor AS= 0.05, 0.1, 0.2, 0.3, 0.4 and 0.5, respectively, in the flow system whose asymmetry is generated by location deviations. In the flow system whose asymmetry is generated by two different flow rates at two outlets, the critical capillary numbers are 0.121, 0.133, 0.145, 0.156 and 0.167 for AS= 1/21, 3/23, 1/5, 7/27 and 9/29, respectively.
文摘The influence of baffle position on liquid sloshing during the braking and turning of a tank truck was studied using a volume of fluid (VOF) model. The forces,their positions and weight distribution during braking and the forces and rolling moment during turning were calculated. The reliability of the calculation method was validated by comparisons with experimental results. The results showed that during braking,liquid splashes in the tank and the maximum forces and G (the ratio of weight acting on the front axle to the rear axle) are large when A (the ratio of the arch area above the baffle to the area of cross section)≤0.1. When A≥0.2,as the position of the baffle is lowered,the maximum of Fx (the force in direction x) first decreases then increases,and the maximum of Fy (the force in direction y) and G increase. During turning,liquid splashes in the tank and the maximum forces and M (the rolling moment) are large when D (the ratio of the arch area above the baffle to the area of cross section)≤0.2. When D≥0.3,as the position of the baffle is lowered,the maximums of Fy,Fz (the force in direction z) and M increase.
文摘Numerous gas-liquid-solid flows exist in chemical engineering and metallurgical processes. Numerical modeling is an important topic that can be used to improve the design and investigate the operating conditions of these processes. The complicated interphase interaction within such three-phase systems, which include free surfaces and discrete phases, poses challenges in the existing methods. We imple- mented a volume-of-fluid （VOF） and discrete-element-method （DEM） combined solver, which should be useful for modeling the gas-liquid-solid systems, within the OpenFOAM framework. The Du Plessis and Masliyah drag force, added mass force, and capillary force were considered for fluid-particle coupling. The VOF-DEM solver was tested in three different cases, namely, particles in pure gas, particle collision in water, and gas-liquid-solid three-phase dam break. The results were validated against previous experi- ments and good agreement was obtained between the simulations and the experiments, which indicates the accuracy and suitability of this VOF-DEM solver for gas-liquid-solid systems.
基金the National Natural Science Foundation of China(Grant No.51876102)the Science Fund for Creative Research Groups of the National Natural Science Foundation of China(Grant No.51621062).
文摘Partial coalescence is a complicated flow phenomenon.In the present study,the coalescence process is simulated with the volume of fluid(VOF)method.The numerical results reveal that a downward high-velocity region plays a significant role in partial coalescence.The high-velocity region pulls the droplet downward continuously which is an important factor for the droplet turning into a prolate shape and the final pinch-off.The shift from partial coalescence to full coalescence is explained based on the droplet shape before the pinch-off.With the droplet impact velocity increasing,the droplet shape will get close to a sphere before the pinch-off.When the shape gets close enough to a sphere,the partial coalescence shifts to full coalescence.The effect of film thickness on the coalescence process is also investigated.With large film thickness,partial coalescence happens,while with small film thickness,full coalescence happens.In addition,the results indicate that the critical droplet impact velocity increases with the increase of surface tension coefficient but decreases with the increase of viscosity and initial droplet diameter.And there is a maximum critical Weber number with the increase of surface tension coefficient and initial droplet diameter.
基金supported by the National Natural Science Foundation of China (Grant Nos. 10672043 and 10272032)
文摘In the inviscid and incompressible fluid flow regime,surface tension effects on the behaviour of an initially spherical buoyancy-driven bubble rising in an infinite and initially stationary liquid are investigated numerically by a volume of fluid （VOF） method. The ratio of the gas density to the liquid density is 0.001, which is close to the case of an air bubble rising in water. It is found by numerical experiment that there exist four critical Weber numbers We1,~We2,~We3 and We4, which distinguish five different kinds of bubble behaviours. It is also found that when 1≤We2, the bubble will finally reach a steady shape, and in this case after it rises acceleratedly for a moment, it will rise with an almost constant speed, and the lower the Weber number is, the higher the speed is. When We 〉We2, the bubble will not reach a steady shape, and in this case it will not rise with a constant speed. The mechanism of the above phenomena has been analysed theoretically and numerically.
