Numerical Study Of The Droplet Impact On The Surface Of A Cylinder

Droplet impact can be seen everywhere in real life,and it is also widely encountered in industrial and aerospace fields,such as the splash of droplets in chemical containers,the oil droplets impact on the wall of the combustion chamber in diesel engines,spray impact on the wall surface caused by fuel injection in the internal combustion engine,droplet impact on aircraft protective cover and helicopter propeller,droplet impact on rotating caps inside the engine.In recent years,many researchers have studied the phenomenon of droplet impact on the wall surface,but most of them focused on the droplet impact on a flat surface.There are few studies of droplet impact on a curved wall,and most numerical studies in this area employed the coupled level set volume of fluid method.In this work,the lattice Boltzmann method based on phase field theory is used to study the droplet impact on the surface of a cylinder,and the changes of the droplet deformation when the fluid property and the wall characteristics are changed are analyzed.The main work includes:(1)The research status of droplet impact and the results of previous research are briefly reviewed.The theoretical,experimental and numerical studies of droplet impact are summarized.It is found that the research of this problem is mostly on the droplet impact on a straight wall,and there are few studies on the droplet impact on a curved wall.(2)The lattice Boltzmann method is briefly introduced,its development and characteristics are reviewed.The specific numerical model used in this paper is given,it is verified by comparing the numerical results of the capillary wave with the theoretical results,by comparing the given contact angle with the numerically deduced results for a droplet on a curved surface and by comparing the results of the droplet impact on a film with existing numerical results in the literature.The convergence study under different grids further verifies the reliability of the model.(3)The dynamic deformation of a droplet with a radius r impacting on the outer surface of a cylinder with a radius R was simulated.Under different physical conditions,the dynamic characteristics of droplet impact are different.The different evolutions of the droplet shape were examined when the initial impact velocity,the viscosity ratio,the relative radius of the cylinder and the wettability of the surface changed.When the initial velocity increases,the droplet splits more easily on the outer surface of the cylinder.The droplet spreading is more obvious under large viscosity ratios,and the retracting trend is weaker.On a more hydrophilic wall,the distance the contact line moves is longer and the spreading is more obvious,on a surface with poor wettability,the droplet is easier to rebound after impacting on the outer surface of a cylinder.(4)The dynamic process of droplet impacting on the inner surface of a cylinder was simulated.Different impact velocities,initial heights of the droplet,surface wettabilities and radii of the cylinder were considered and their effects on the evolution of the droplet shape were investigated.The physical properties of the fluids including the density and viscosity were also varied to assess their effects on the impact outcome.It was found that the impact Weber number,the liquid/gas density and viscosity ratios,the wettability of the inner surface of the cylinder,and the radius of the cylinder may have significant effects on the deformation and spreading of the droplet.When the Weber number is high enough,droplet splashing appears.When the density and viscosity ratios are high,the initial height of the droplet only has minor effect on the impact results.Rebound of the droplet may be observed when the contact angle of the inner surface of the cylinder is large enough.Besides,the gravity force was found to suppress the oscillation of the droplet after its impact.