Modeling and Simulation of Sealing Spray Application Using Smoothed Particle Hydrodynamics

Multiphase flow simulation using Smoothed Particle Hydrodynamics (SPH)has gained interest during recent years, mostly due to the inherentflexibility of the method and the physically rather intuitiveformulation of extra constitutive equations needed when dealing withfor instance non-Newtonian flows. In the work presented here,simulations based on an SPH model implemented in the flow solverIBOFlow has been used for simulation of robotic application of sealingmaterial on a car body. Application of sealing materials is done inorder to prevent water leakage into cavities of the body, and toreduce noise. In off-line programming of the robots in the automotivepaintshop it is of great interest to predict shape and appearance ofsealing material without having to resort to trial and errorprocedures.The flow of sealing material in the air between applicator and target(car body) is relatively uncomplicated, as the material mostly movesat constant velocity until impact on target. The flow of the materialon the target is however more complex, applied material flows at thetarget surface due to inertia, gravity and pressure and in order topredict the appearance of the applied material, flow equations for anon-Newtonian fluid with an open surface needs to be solved. Thesealing material is both thixotropic and viscoelastic; the material isshear thinning but needs to be sheared for some time before thestructure of the material is broken down. Conversely, the regain ofstructure of the material, and thereby also the increase of viscositywhen shearing is stopped or reduced, is also connected to a delaytime. In the model used, the local viscosity is considered obeying afirst order differential equation where the stationary limit isdetermined by a Bingham relation.The simulation model was built by comparing simulations andexperiments at three different stages of complexity. In the mostfundamental stage the material properties were determined. Using arotational rheometer, yield stress, plastic viscosity and thixotropytime constant was determined and implemented in the simulation model.To verify the numerical behaviour of the rheology, simulated rheometerexperiments were carried out and compared with the physicalexperiments. In the second stage, simulation of application of sealingmaterial with a stationary hollowcone nozzle was carried out. Toverify the simulations, the resulting thickness, width and shape ofapplied material as a function of time were compared to experiments.In the third stage a moving applicator of the same type wasconsidered, here thickness width and shape of applied material as afunction of applicator to target distances were compared betweenexperiments and simulation. At all three stages the number of SPHparticles, /i.e./ grid points, in the simulations was varied in orderto verify that the simulations were resolution independent.Results of the simulations show good agreement between experiments andsimulations in all stages using no artificial tuning of the models,that is, all parameters used in the models are based on physicalconsiderations. Furthermore, simulation time on a desktop computerindicate that computational power required for industrially relevantcases is not prohibitively large, for the most complex cases in thiswork simulation time did not exceed six hours