Study Of Numerical Simulation About Automotive Dusting Based On The General Inflow Concentration Conditions

The environmental pollution problem is increasingly prominent in recent years.The environmental pollution caused by motor vehicles problem is especially striking.Related studies show that second-time dusting from road caused by motor vehicleaccounts for30-50%of the total particulate matters in the city.Uneven transient airflowfield is formed when the vehicle is moving, which acts on the particles located at theground to produce dusting.The velocity gradient field perpendicular to the ground willdrive the particles the to start and promote the particles further movement and migration.Current research methods on dusting problem by motor vehicles have theoreticalresearch, numerical simulation and experimental research. Numerical simulation is thebetter method to study the spatial and temporal distribution of automotive dusting thanothers.This paper simply analyzes the mechanism of dust injection. Through the relevantparticle starting theory to summary the particle mathematical model. In order to avoidthose existing concentration conditions with overall uniform inflow intensity or thepredefined local inflow intensity and make the injection of particles more real, wediscriminated the movements of the bed dust load and the suspended dust load and thendeduced the concentration expression of bed load according to the local flow fieldconditions. Applying the principle of continuous distribution, this expression was set asthe dusting inflow condition from the ground. Once suspended particles inject into theflow field，it can be accurately described by the convection-diffusion equation. And theconvection diffusion equation is simplified. Consider turbulent diffusion and ignoremolecular diffusion, and the turbulent diffusion coefficient is equal to the momentum exchange coefficient based on Reynolds analogy.This paper used turbulence module provided by COMSOL to simulate the velocityfield and matter transfer module respectively to simulate the concentration field. Inorder to analyze the difference between the relative coordinate and the actual coordinate.Through the moving grid method to get the velocity field, and compared with therelative coordinate velocity field. It is found that the relative coordinates can be wellobtained velocity field. And then based on this method to creat3D models to study theeffects of gravity, wheel rotation, automotive speed and other factors on dusting causedby automotive.The results show that this condition deduced from bed load theory reflects theboundary conditions and can be simulated car starter dust problem. Using themomentum coefficient instead of turbulent diffusion coefficient can reflect theconcentration field. In the three-dimensional numerical simulation, by comparing theresults, it can be concluded that there was no significant different whether thegravitational effect was included or not. The wheel rotation gave the bigger contributionfor a moving automobile with low speed than that with high speed. The approximateexponential relationship between the automotive speed and the dusting amount wasnoticed. The relationship between speed and height dust is exponential decay trend. It isderived from the analysis of transient diffusion results that the characteristic time of thepollutants from cars at the tail1.7m reduced to the international standards is6-8s. Thisis the result of joint action by the strength of the starting amount of pollutants and theturbulent diffusion.