Study On Dynamic Characteristics Of Viscoelastic Droplets Impacting On Wall

The droplet collision phenomenon is widely used in nature and industry.For example,inkjet printing,pesticide spraying,fuel injection and so on are all closely related to droplet collision.The viscoelastic droplet has created more opportunities and innovations for production and life due to its unique fluid properties such as shear thinning,but so far,there are few related researches.Therefore,this paper intends to systematically study the dynamic behavior of droplets impacting the wall by using two methods: numerical simulation and experimental research.The coupling method(CLSVOF)of Level Set and Volume of Fluid(VOF)is used to simulate the impact of droplets on the wall,the effects of droplet type,PAM concentration,surfactant concentration,droplet initial velocity and size on droplet spreading width and rebound height were investigated.The results show that droplets would go through four stages: expansion,contraction,rebound and stable oscillation after collision.In the expansion stage,the spreading width of polyacrylamide(PAM)droplets is smaller than that of water droplets,and increases with the increase of surfactant concentration,initial velocity and size of droplets,but decreases with the increase of PAM concentration.In the contraction and rebound stages,the rebound height of PAM droplets is smaller than that of water droplets,and increases with the increase of PAM concentration,initial velocity and size of the droplets,but decreases with the increase of surfactant concentration.In the stable oscillation stage,the oscillation period of PAM droplets is shorter than that of water droplets;the increase of PAM concentration has no obvious effect on the oscillation period of droplets;while the increase of surfactant concentration,droplet initial velocity and size will prolong the oscillation period of droplets.What’s more,when the initial velocity is large enough,the droplet would shrink and break.The effects of droplet type,PAM concentration,surfactant concentration,falling height and wall wettability on droplet impact behavior were investigated by experimental methods.The results show that the spreading width and rebound height of PAM droplets are smaller than that of water droplets under the same conditions,which is consistent with the simulation results.The spreading width of PAM droplets increases with the increase of surfactant concentration and drop height,but decreases with the increase of PAM concentration and wall wettability.The rebound height of the droplets increases with the increase of PAM concentration,wall wettability and falling height,but decreases with the increase of surfactant concentration.