This work is concerned with the modelling of the interaction of fluid flow with flexibly supported rigid bodies.The fluid flow is modelled by Lattice-Boltzmann Method,coupled to a set of ordinary differential equation...This work is concerned with the modelling of the interaction of fluid flow with flexibly supported rigid bodies.The fluid flow is modelled by Lattice-Boltzmann Method,coupled to a set of ordinary differential equations describing the dynamics of the solid body in terms its elastic and damping properties.The time discretization of the body dynamics is performed via the Time Discontinuous Galerkin Method.Several numerical examples are presented and highlight the robustness and efficiency of the proposed methodology,by means of comparisons with previously published results.The examples show that the present fluid-structure method is able to capture vortexinduced oscillations of flexibly-supported rigid body.展开更多
The onset of cavitating conditions inside the nozzle of liquid injectors is known to play a major role on spray characteristics,especially on jet penetration and break-up.In this work,we present a Direct Numerical Sim...The onset of cavitating conditions inside the nozzle of liquid injectors is known to play a major role on spray characteristics,especially on jet penetration and break-up.In this work,we present a Direct Numerical Simulation(DNS)based on the Lattice Boltzmann Method(LBM)to study the fluid dynamic field inside the nozzle of a cavitating injector.The formation of the cavitating region is determined via a multi-phase approach based on the Shan-Chen equation of state.The results obtained by the LBM simulation show satisfactory agreement with both numerical and experimental data.In addition,numerical evidence of bubble break-up,following upon flow-induced cavitation,is also reported.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
This paper presents a new finite-volume discretization of a generalised LatticeBoltzmann equation (LBE) on unstructured grids. This equation is the continuumLBE, with the addition of a second order time derivative ter...This paper presents a new finite-volume discretization of a generalised LatticeBoltzmann equation (LBE) on unstructured grids. This equation is the continuumLBE, with the addition of a second order time derivative term (memory), and is derivedfrom a second-order differential form of the semi-discrete Boltzmann equationin its implicit form. The new scheme, named unstructured lattice Boltzmann equationwith memory (ULBEM), can be advanced in time with a larger time-step than the previousunstructured LB formulations, and a theoretical demonstration of the improvedstability is provided. Taylor vortex simulations show that the viscosity is the same aswith standard ULBE and demonstrates that the new scheme improves both stabilityand accuracy. Model validation is also demonstrated by simulating backward-facingstep flow at low and moderate Reynolds numbers, as well as by comparing the reattachmentlength of the recirculating eddy behind the step against experimental andnumerical data available in literature.展开更多
The simulation of multiphase flows is an outstanding challenge,due to the inherent complexity of the underlying physical phenomena and to the fact that multiphase flows are very diverse in nature,and so are the laws g...The simulation of multiphase flows is an outstanding challenge,due to the inherent complexity of the underlying physical phenomena and to the fact that multiphase flows are very diverse in nature,and so are the laws governing their dynamics.In the last two decades,a new class of mesoscopic methods,based on minimal lattice formulation of Boltzmann kinetic equation,has gained significant interest as an efficient alternative to continuum methods based on the discretisation of the NS equations for non ideal fluids.In this paper,three different multiphase models based on the lattice Boltzmann method(LBM)are discussed,in order to assess the capability of the method to deal with multiphase flows on a wide spectrum of operating conditions and multiphase phenomena.In particular,the range of application of each method is highlighted and its effectiveness is qualitatively assessed through comparison with numerical and experimental literature data.展开更多
文摘This work is concerned with the modelling of the interaction of fluid flow with flexibly supported rigid bodies.The fluid flow is modelled by Lattice-Boltzmann Method,coupled to a set of ordinary differential equations describing the dynamics of the solid body in terms its elastic and damping properties.The time discretization of the body dynamics is performed via the Time Discontinuous Galerkin Method.Several numerical examples are presented and highlight the robustness and efficiency of the proposed methodology,by means of comparisons with previously published results.The examples show that the present fluid-structure method is able to capture vortexinduced oscillations of flexibly-supported rigid body.
文摘The onset of cavitating conditions inside the nozzle of liquid injectors is known to play a major role on spray characteristics,especially on jet penetration and break-up.In this work,we present a Direct Numerical Simulation(DNS)based on the Lattice Boltzmann Method(LBM)to study the fluid dynamic field inside the nozzle of a cavitating injector.The formation of the cavitating region is determined via a multi-phase approach based on the Shan-Chen equation of state.The results obtained by the LBM simulation show satisfactory agreement with both numerical and experimental data.In addition,numerical evidence of bubble break-up,following upon flow-induced cavitation,is also reported.
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.
文摘This paper presents a new finite-volume discretization of a generalised LatticeBoltzmann equation (LBE) on unstructured grids. This equation is the continuumLBE, with the addition of a second order time derivative term (memory), and is derivedfrom a second-order differential form of the semi-discrete Boltzmann equationin its implicit form. The new scheme, named unstructured lattice Boltzmann equationwith memory (ULBEM), can be advanced in time with a larger time-step than the previousunstructured LB formulations, and a theoretical demonstration of the improvedstability is provided. Taylor vortex simulations show that the viscosity is the same aswith standard ULBE and demonstrates that the new scheme improves both stabilityand accuracy. Model validation is also demonstrated by simulating backward-facingstep flow at low and moderate Reynolds numbers, as well as by comparing the reattachmentlength of the recirculating eddy behind the step against experimental andnumerical data available in literature.
文摘The simulation of multiphase flows is an outstanding challenge,due to the inherent complexity of the underlying physical phenomena and to the fact that multiphase flows are very diverse in nature,and so are the laws governing their dynamics.In the last two decades,a new class of mesoscopic methods,based on minimal lattice formulation of Boltzmann kinetic equation,has gained significant interest as an efficient alternative to continuum methods based on the discretisation of the NS equations for non ideal fluids.In this paper,three different multiphase models based on the lattice Boltzmann method(LBM)are discussed,in order to assess the capability of the method to deal with multiphase flows on a wide spectrum of operating conditions and multiphase phenomena.In particular,the range of application of each method is highlighted and its effectiveness is qualitatively assessed through comparison with numerical and experimental literature data.
