Experimental And Numerical Study On The Droplet Formation Characteristics Of Newtonian Fluid

Droplet formation is a very normal phenomenon in nature,and it is widely used in scientific research,industrial production and other fields,such as liquid extraction,biomedical,inkjet printing,and internal combustion engines,etc.So it has very important practical significance on the research of droplet formation.Due to the complex and subtle morphological changes of droplet formation and drop process,it is quite difficult in the research process.In order to deeply understand the subtle changes of the droplet formation process and to study the effects of concentration,velocity and other influencing factors on its formation,this paper studied the formation process through the combination of experiments and numerical simulation taking glycerol solution as the research object.An experimental platform was set up to capture the morphological evolution of droplet formation processes with different flow rates and different concentrations in combination with a high-speed photography system.The time series images of droplet formation and drop were obtained,and the influence of concentration and flow rates on droplet formation was studied.Using the VOF method and geometric reconstruction,the interface of the droplet formation was captured.The distribution of the velocity vector and the pressure distribution of the droplet during the formation process and the situation of the falling oscillation were analyzed.The following results were obtained.(1)Droplet formation process of capillary end was analyzed by numerical simulation method in low flow rates and compared with the experiment to verify the feasibility of the numerical simulation.And the droplet formation process is divided to three stages: formation,neck and breakage.(2)Experiments were carried out to determine the formation of droplets at different flow rates.The relationship between the flow rates and the pressure and axial velocity was analyzed at the breakage stage.The axial velocity shows the position of the vortex,and the resultant forces of the droplet formation under different flow rates is analyzed,and the relationship between the flow rate and the break volume is deduced.It is analyzed that the flow rates does not change the period of the droplet oscillation.(3)Different concentrations experiments of droplet formation were carried out to study the relationship between the thread length and concentration.The greater the concentration,the longer the thread formed.The relationship between droplet concentration and amplitude is studied.With the increase of liquid viscosity,the oscillation amplitude decrease accordingly.The oscillation period does not change with the viscosity,and the viscosity has an absorption effect on the oscillation of the drop.(4)The relationship between concentrations and internal pressure and axial velocity of the droplets was studied,and the maximum pressure and the maximum axial velocity appear in the position of the neck.The force of the droplets in the formation process was analyzed,and the reason for the droplet breakage was explained.