A droplet undergoes spreading,rebounding or splashing when it impacts solid boundary,which is a typical phenomenon of free surface flow that exists widely in modern industry.Smoothed particle hydrodynamics(SPH)method ...A droplet undergoes spreading,rebounding or splashing when it impacts solid boundary,which is a typical phenomenon of free surface flow that exists widely in modern industry.Smoothed particle hydrodynamics(SPH)method is applied to numerically study the dynamical behaviors of the droplet impacting solid boundary,and both the spreading and rebounding phenomena of the droplet are reproduced in the simulation.The droplet deformation,flow fields and pressure fields inside the droplet at different moments are analyzed.Two important factors,the initial velocity and diameter,are discussed in determining the maximum spreading factor,revealing that the maximum spreading factor increases with the increase of the impact velocity and droplet diameter respectively.展开更多
Electrostatic delivery of charged uniform metal droplets is a novel method to deposit metal parts with short process period and low cost. But the delivery process is unstable and delivery accuracy of charged droplets ...Electrostatic delivery of charged uniform metal droplets is a novel method to deposit metal parts with short process period and low cost. But the delivery process is unstable and delivery accuracy of charged droplets deteriorates because of actions of mutual interactions of closely charged droplets. A droplet generator with droplet charging and deflecting system has been established to find out the way for stably and accurately deflecting droplets. The parameters for generating uniform droplets were first studied. Then the droplet deflections and metal parts depositions with different charge methods were discussed. The results show that the unbalanced electrostatic repelling forces are the main factor to cause the unstable deflection of droplets. The droplets deflection distance can be predicted and controlled by balancing the repelling forces of charged droplets. The metal parts are stably deposited after combining the board charged pulse and substrate motion, indicating that the work can provide useful theoretical and experimental guide for droplet-based freeform fabrication.展开更多
Droplet impacting liquid surface is not only the extremely prevalent phenomenon in the nature and industrial production but also the extremely complicated problem of strong non-linear transient impact and free-surface...Droplet impacting liquid surface is not only the extremely prevalent phenomenon in the nature and industrial production but also the extremely complicated problem of strong non-linear transient impact and free-surface flow. On the basis of the two-dimensional viscous incompressible N-S equations, this paper conducts a study of numerical simulation on the problem of droplet impacting liquid surface （water beads） of water container in certain initial velocity by the method of SPH （smoothed particle hydrodynamics）. The effect of surface tension is considered between surface particles by searching the free surface particles in the course of study; the effect of initial impact has been solved by use of artificial viscosity; at the same time, the side-wall virtual particles and image virtual particles are both introduced to deal with the boundary condition, which has solved the boundary defects quite well and eliminated the instability of real particles dropped to the comer of container. The calculated results form the distribution chart of particles, flow field chart, pressure chart and the displacement and velocity variation curve of different particles. The comparison between simulated results and experimental photos shows that the simulation is effective. This paper compares the variational curves for fluctuations of liquid surface qualitatively through adopting the methods of level-set, BEM and SPH, respectively at last. The simulated results show that it will produce strong non-linear phenomena, such as the splash of liquid, discrete liquid surface, and strong wave of free liquid surface, when the droplet impacts liquid surface; in the course of impacting, the movement of liquid particles exhibits the characteristic of oscillation; the method of SPH has certain advantages of dealing with the large deformation problem of free surface.展开更多
基金Supported by the National Natural Science Foundation of China(No.51079095)the Science Fund for Creative Research Groups of the National Natural Science Foundation of China(No.51021004)
文摘A droplet undergoes spreading,rebounding or splashing when it impacts solid boundary,which is a typical phenomenon of free surface flow that exists widely in modern industry.Smoothed particle hydrodynamics(SPH)method is applied to numerically study the dynamical behaviors of the droplet impacting solid boundary,and both the spreading and rebounding phenomena of the droplet are reproduced in the simulation.The droplet deformation,flow fields and pressure fields inside the droplet at different moments are analyzed.Two important factors,the initial velocity and diameter,are discussed in determining the maximum spreading factor,revealing that the maximum spreading factor increases with the increase of the impact velocity and droplet diameter respectively.
基金supported by the National High Technology Research and Development Program of China ("863"Program) (Grant No. 2008AA03A238)the National Natural Science Foundation of China (Grant No. 51005186)Foundation for the Author of National Excellent Doctoral Dissertation of China (Grant No. 2007B3)
文摘Electrostatic delivery of charged uniform metal droplets is a novel method to deposit metal parts with short process period and low cost. But the delivery process is unstable and delivery accuracy of charged droplets deteriorates because of actions of mutual interactions of closely charged droplets. A droplet generator with droplet charging and deflecting system has been established to find out the way for stably and accurately deflecting droplets. The parameters for generating uniform droplets were first studied. Then the droplet deflections and metal parts depositions with different charge methods were discussed. The results show that the unbalanced electrostatic repelling forces are the main factor to cause the unstable deflection of droplets. The droplets deflection distance can be predicted and controlled by balancing the repelling forces of charged droplets. The metal parts are stably deposited after combining the board charged pulse and substrate motion, indicating that the work can provide useful theoretical and experimental guide for droplet-based freeform fabrication.
基金supported by the National Natural Science Foundation of China (Grant Nos. 51079095, 51021004)
文摘Droplet impacting liquid surface is not only the extremely prevalent phenomenon in the nature and industrial production but also the extremely complicated problem of strong non-linear transient impact and free-surface flow. On the basis of the two-dimensional viscous incompressible N-S equations, this paper conducts a study of numerical simulation on the problem of droplet impacting liquid surface （water beads） of water container in certain initial velocity by the method of SPH （smoothed particle hydrodynamics）. The effect of surface tension is considered between surface particles by searching the free surface particles in the course of study; the effect of initial impact has been solved by use of artificial viscosity; at the same time, the side-wall virtual particles and image virtual particles are both introduced to deal with the boundary condition, which has solved the boundary defects quite well and eliminated the instability of real particles dropped to the comer of container. The calculated results form the distribution chart of particles, flow field chart, pressure chart and the displacement and velocity variation curve of different particles. The comparison between simulated results and experimental photos shows that the simulation is effective. This paper compares the variational curves for fluctuations of liquid surface qualitatively through adopting the methods of level-set, BEM and SPH, respectively at last. The simulated results show that it will produce strong non-linear phenomena, such as the splash of liquid, discrete liquid surface, and strong wave of free liquid surface, when the droplet impacts liquid surface; in the course of impacting, the movement of liquid particles exhibits the characteristic of oscillation; the method of SPH has certain advantages of dealing with the large deformation problem of free surface.
