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Staffan September 1, 2000 04:24

Near wall particles
 
Hi,

I'm simulating particle flow in a combustion chamber. My particles are of the sizes: 0.0001m, 1e-5m and 1e-6m. The problem is that small particles hits the walls as often as the bigger ones. In reality the small ones should follow the gasflow. How does fluent calculate near wall threatment of particles? a.) Is a particle considerd as trapped (escaped or reflexed) when it enters the cell next to the wall or when the particle actually hits the wall? b.)Does the mesh size near the boundaries influence the results of the near wall threatment of particles?

Thanks, Staffan

Rüdiger Schwarze September 4, 2000 13:38

Re: Near wall particles
 
I've got the same unphysical results in a similar problem. I think that the drw model is responsible for these errors. The particle obtains a fluctuating velocity u' in the free flow field and an eddy life time which is much more longer the the flying time through the boundary layer.

Hesham El-Batsh October 2, 2000 09:47

Re: Near wall particles
 
I think the turbulence model has great effect. For example, the standard k-e model is a fully turbulent model and generates high turbulent knietic energy which affects the particle fluctuating velocity used in RWM and finally increases the number of particles hitting the surface. To accurately predict particle dispersion near the wall using RWM, low Reynolds number models are required. The other possibility is to use damping functions in the near wall region. One of the damping functions can be found in this reference: Wang, Y. and James, P. W. "On the Effect of Anisotropy on the Turbulent Dispersion and Deposition of Small Particles" International Journal of Multiphase flow, v. 25, pp. 551-558, 1999


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