The immersed boundary method has emerged as an efficient approach for the simulation of finite-sized solid particles in complex fluid flows.However,one of the well known shortcomings of the method is the limited suppo...The immersed boundary method has emerged as an efficient approach for the simulation of finite-sized solid particles in complex fluid flows.However,one of the well known shortcomings of the method is the limited support for the simulation of light particles,i.e.particles with a density lower than that of the surrounding fluid,both in terms of accuracy and numerical stability.Although a broad literature exists,with several authors reporting different approaches for improving the stability of the method,most of these attempts introduce extra complexities and are very costly from a computational point of view.In this work,we introduce an effective force stabilizing technique,allowing to extend the stability range of the method by filtering spurious oscillations arising when dealing with light-particles,pushing down the particle-to-fluid density ratio as low as 0.04.We thoroughly validate the method comparing with both experimental and numerical data available in literature.展开更多
Multicomponent models based on the Lattice Boltzmann Method(LBM)have clear advantages with respect to other approaches,such as good parallel performances and scalability and the automatic resolution of breakup and coa...Multicomponent models based on the Lattice Boltzmann Method(LBM)have clear advantages with respect to other approaches,such as good parallel performances and scalability and the automatic resolution of breakup and coalescence events.Multicomponent flow simulations are useful for a wide range of applications,yet many multicomponent models for LBMare limited in their numerical stability and therefore do not allow exploration of physically relevant low viscosity regimes.Here we performa quantitative study and validations,varying parameters such as viscosity,droplet radius,domain size and acceleration for stationary and translating droplet simulations for the color-gradientmethod with centralmoments(CG-CM)formulation,as this method promises increased numerical stability with respect to the non-CMformulation.We focus on numerical stability and on the effect of decreasing grid-spacing,i.e.increasing resolution,in the extremely low viscosity regime for stationary droplet simulations.The effects of small-and large-scale anisotropy,due to grid-spacing and domain-size,respectively,are investigated for a stationary droplet.The effects on numerical stability of applying a uniform acceleration in one direction on the domain,i.e.on both the droplet and the ambient,is explored into the low viscosity regime,to probe the numerical stability of the method under dynamical conditions.展开更多
We show that the lattice Boltzmann method(LBM)based color-gradient model with a central moments formulation(CG-CM)is capable of accurately simulating the droplet-on-demand inkjetting process on a micrometer length sca...We show that the lattice Boltzmann method(LBM)based color-gradient model with a central moments formulation(CG-CM)is capable of accurately simulating the droplet-on-demand inkjetting process on a micrometer length scale by comparing it to the Arbitrary Lagrangian Eulerian Finite Element Method(ALE-FEM).A full jetting cycle is simulated using both CG-CM and ALE-FEMand results are quantitatively compared by measuring the ejected ink velocity,volume and contraction rate.We also show that the individual relevant physical phenomena are accurately captured by considering three test-cases;droplet oscillation,ligament contraction and capillary rise.The first two cases test accuracy for a dynamic system where surface tension is the driving force and the third case is designed to test wetting boundary conditions.For the first two cases we also compare the CG-CM and ALE-FEM results to Volume of Fluid(VOF)simulations.Comparison of the three methods shows close agreement when compared to each other and analytical solutions,where available.Finally we demonstrate that asymmetric jetting is achievable using 3D CG-CM simulations utilizing asymmetric wetting conditions inside the jet-nozzle.This allows for systematic investigation into the physics of asymmetric jetting,e.g.due to jet-nozzle manufacturing imperfections or due to other disturbances.展开更多
The performances of the Color-Gradient(CG)and the Shan-Chen(SC)multicomponent Lattice Boltzmann models are quantitatively compared side-by-side on multiple physical flow problems where breakup,coalescence and contract...The performances of the Color-Gradient(CG)and the Shan-Chen(SC)multicomponent Lattice Boltzmann models are quantitatively compared side-by-side on multiple physical flow problems where breakup,coalescence and contraction of fluid ligaments are important.The flow problems are relevant to microfluidic applications,jetting of microdroplets as seen in inkjet printing,as well as emulsion dynamics.A significantly wider range of parameters is shown to be accessible for CG in terms of density-ratio,viscosity-ratio and surface tension values.Numerical stability for a high density ratio O(1000)is required for simulating the drop formation process during inkjet printing which we show here to be achievable using the CG model but not using the SC model.Our results show that the CG model is a suitable choice for challenging simulations of droplet formation,due to a combination of both numerical stability and physical accuracy.We also present a novel approach to incorporate repulsion forces between interfaces for CG,with possible applications to the study of stabilized emulsions.Specifically,we show that the CG model can produce similar results to a known multirange potentials extension of the SC model for modelling a disjoining pressure,opening up its use for the study of dense stabilized emulsions.展开更多
Over the last decade the Lattice Boltzmann Method (LBM) has gained significant interest as a numerical solver for multiphase flows. However most of the LBvariants proposed to date are still faced with discreteness art...Over the last decade the Lattice Boltzmann Method (LBM) has gained significant interest as a numerical solver for multiphase flows. However most of the LBvariants proposed to date are still faced with discreteness artifacts in the form of spurious currents around fluid-fluid interfaces. In the recent past, Lee et al. have proposeda new LB scheme, based on a higher order differencing of the non-ideal forces, whichappears to virtually free of spurious currents for a number of representative situations.In this paper, we analyze the Lee method and show that, although strictly speaking, itlacks exact mass conservation, in actual simulations, the mass-breaking terms exhibita self-stabilizing dynamics which leads to their disappearance in the long-term evolution. This property is specifically demonstrated for the case of a moving droplet atlow-Weber number, and contrasted with the behaviour of the Shan-Chen model. Furthermore, the Lee scheme is for the first time applied to the problem of gravity-drivenRayleigh-Taylor instability. Direct comparison with literature data for different values of the Reynolds number, shows again satisfactory agreement. A grid-sensitivitystudy shows that, while large grids are required to converge the fine-scale details, thelarge-scale features of the flow settle-down at relatively low resolution. We concludethat the Lee method provides a viable technique for the simulation of Rayleigh-Taylorinstabilities on a significant parameter range of Reynolds and Weber numbers.展开更多
文摘The immersed boundary method has emerged as an efficient approach for the simulation of finite-sized solid particles in complex fluid flows.However,one of the well known shortcomings of the method is the limited support for the simulation of light particles,i.e.particles with a density lower than that of the surrounding fluid,both in terms of accuracy and numerical stability.Although a broad literature exists,with several authors reporting different approaches for improving the stability of the method,most of these attempts introduce extra complexities and are very costly from a computational point of view.In this work,we introduce an effective force stabilizing technique,allowing to extend the stability range of the method by filtering spurious oscillations arising when dealing with light-particles,pushing down the particle-to-fluid density ratio as low as 0.04.We thoroughly validate the method comparing with both experimental and numerical data available in literature.
基金the Netherlands Organization for Scientific Research(NWO)research project High Tech Systems and Materials(HTSM),with project number 13912.
文摘Multicomponent models based on the Lattice Boltzmann Method(LBM)have clear advantages with respect to other approaches,such as good parallel performances and scalability and the automatic resolution of breakup and coalescence events.Multicomponent flow simulations are useful for a wide range of applications,yet many multicomponent models for LBMare limited in their numerical stability and therefore do not allow exploration of physically relevant low viscosity regimes.Here we performa quantitative study and validations,varying parameters such as viscosity,droplet radius,domain size and acceleration for stationary and translating droplet simulations for the color-gradientmethod with centralmoments(CG-CM)formulation,as this method promises increased numerical stability with respect to the non-CMformulation.We focus on numerical stability and on the effect of decreasing grid-spacing,i.e.increasing resolution,in the extremely low viscosity regime for stationary droplet simulations.The effects of small-and large-scale anisotropy,due to grid-spacing and domain-size,respectively,are investigated for a stationary droplet.The effects on numerical stability of applying a uniform acceleration in one direction on the domain,i.e.on both the droplet and the ambient,is explored into the low viscosity regime,to probe the numerical stability of the method under dynamical conditions.
基金the Netherlands Organization for Scientific Research(NWO)research project High Tech Systems and Materials(HTSM),with project number 13912the NWO and co-financers Canon Production Printing Holding B.V.,University of Twente and Eindhoven University of Technology for financial support.This work was carried out on the Dutch national e-infrastructure with the support of SURF Cooperative,project number 2021.035。
文摘We show that the lattice Boltzmann method(LBM)based color-gradient model with a central moments formulation(CG-CM)is capable of accurately simulating the droplet-on-demand inkjetting process on a micrometer length scale by comparing it to the Arbitrary Lagrangian Eulerian Finite Element Method(ALE-FEM).A full jetting cycle is simulated using both CG-CM and ALE-FEMand results are quantitatively compared by measuring the ejected ink velocity,volume and contraction rate.We also show that the individual relevant physical phenomena are accurately captured by considering three test-cases;droplet oscillation,ligament contraction and capillary rise.The first two cases test accuracy for a dynamic system where surface tension is the driving force and the third case is designed to test wetting boundary conditions.For the first two cases we also compare the CG-CM and ALE-FEM results to Volume of Fluid(VOF)simulations.Comparison of the three methods shows close agreement when compared to each other and analytical solutions,where available.Finally we demonstrate that asymmetric jetting is achievable using 3D CG-CM simulations utilizing asymmetric wetting conditions inside the jet-nozzle.This allows for systematic investigation into the physics of asymmetric jetting,e.g.due to jet-nozzle manufacturing imperfections or due to other disturbances.
基金part of the Netherlands Organization for Scientific Research(NWO)research project High Tech Systems and Materials(HTSM),with project number 13912the NWO and co-financers Canon Production Printing Holding B.V.,University of Twente and Eindhoven University of Technology for financial support.
文摘The performances of the Color-Gradient(CG)and the Shan-Chen(SC)multicomponent Lattice Boltzmann models are quantitatively compared side-by-side on multiple physical flow problems where breakup,coalescence and contraction of fluid ligaments are important.The flow problems are relevant to microfluidic applications,jetting of microdroplets as seen in inkjet printing,as well as emulsion dynamics.A significantly wider range of parameters is shown to be accessible for CG in terms of density-ratio,viscosity-ratio and surface tension values.Numerical stability for a high density ratio O(1000)is required for simulating the drop formation process during inkjet printing which we show here to be achievable using the CG model but not using the SC model.Our results show that the CG model is a suitable choice for challenging simulations of droplet formation,due to a combination of both numerical stability and physical accuracy.We also present a novel approach to incorporate repulsion forces between interfaces for CG,with possible applications to the study of stabilized emulsions.Specifically,we show that the CG model can produce similar results to a known multirange potentials extension of the SC model for modelling a disjoining pressure,opening up its use for the study of dense stabilized emulsions.
文摘Over the last decade the Lattice Boltzmann Method (LBM) has gained significant interest as a numerical solver for multiphase flows. However most of the LBvariants proposed to date are still faced with discreteness artifacts in the form of spurious currents around fluid-fluid interfaces. In the recent past, Lee et al. have proposeda new LB scheme, based on a higher order differencing of the non-ideal forces, whichappears to virtually free of spurious currents for a number of representative situations.In this paper, we analyze the Lee method and show that, although strictly speaking, itlacks exact mass conservation, in actual simulations, the mass-breaking terms exhibita self-stabilizing dynamics which leads to their disappearance in the long-term evolution. This property is specifically demonstrated for the case of a moving droplet atlow-Weber number, and contrasted with the behaviour of the Shan-Chen model. Furthermore, the Lee scheme is for the first time applied to the problem of gravity-drivenRayleigh-Taylor instability. Direct comparison with literature data for different values of the Reynolds number, shows again satisfactory agreement. A grid-sensitivitystudy shows that, while large grids are required to converge the fine-scale details, thelarge-scale features of the flow settle-down at relatively low resolution. We concludethat the Lee method provides a viable technique for the simulation of Rayleigh-Taylorinstabilities on a significant parameter range of Reynolds and Weber numbers.
