Application Research Of CFD-DEM Coupling Method In Standard Experimental Simulation Of Stone-impact Resistance Performance Of Automotive Coatings

The stone-impact resistance performance of automotive coatings is very important to the safety and aesthetics of automobiles.In recent years,it has attracted the attention of many scholars and related companies at home and abroad.At present,the research on the stone-impact resistance performance of automotive coatings mainly relies on standard equivalent experiments,and there is no corresponding numerical simulation method to analyze such problems.In order to realize the simulation evaluation for the stone-impact resistance performance of automotive coatings,this paper researches and analyzes the fluid-particle twophase motion in the standard experiment process.The main contents include:Based on full investigation and analysis of Computational Fluid Dynamics(CFD),Discrete Element Method(DEM)and their coupling method(CFD-DEM),especially the Immersed Boundary Method(IBM),a new numerical simulation method is proposed.A large particle can be divided into several non-overlapping spherical particles smaller than the grid size of the flow field,through the Bonded-Particle Model(BPM)or the method of multi-particle rigidization.The interaction between the fluid and the large particle is simulated in the framework of the unresolved CFD-DEM method,and the average values of the motion parameters of all small spherical particles are used to describe the overall motion state.In the open-source software framework CFDEM,the IBM and unresolved CFD-DEM combined with BPM or particle rigidization method are implemented.By simulating the settlement motion of large particles in viscous fluid,the accuracy and applicability of the two methods are compared and analyzed.The simulation results of the settlement motion of single and multiple large spherical particles prove that the unresolved CFD-DEM combined with BPM(or particle rigidization)and the IBM can accurately simulate the settlement motion of large spherical particles in the fluid,but the calculation efficiency of the former is significantly higher than the latter.And it is difficult to apply the IBM to simulate the motion of three-dimensional non-spherical large particles in the fluid.The cases of single cube,ellipsoidal particles and multiple cubic particles settlement in viscous fluid prove that the unresolved CFD-DEM combined with BPM(or particle rigidization)can efficiently simulate the motion of large non-spherical particles in the fluid in three dimensions.The simulation models for the standard experiments of coating particle impact of DIN and SAE systems are established.The comparisons of the experimental and simulation results of single and multiple steel spheres driven by high-speed air in a horizontal tube under the conditions of high gas velocity and high Reynolds numbers prove that the simulation results of the IBM method are not accurate enough and the calculation efficiency is too low.It is not suitable for the simulation of the standard experiments process of the DIN and SAE systems.The unresolved CFD-DEM combined with particle rigidization method can accurately and efficiently simulate the experimental process.Applying it to DIN and SAE standard experimental process simulations,can effectively simulate the movement of the flow field and particle field during the experiment,and obtain the specific velocities and positions information of each particle when hitting the coating sample.In summary,the fluid-particle two-phase motion during the standard experimental process of the coatings’ stone-impact resistance can be simulated based on the CFD-DEM method proposed in this paper,which provides a basis for the simulation evaluation of the stone-impact resistance performance of automotive coatings.