# Velocity fluctuation distribution near a wall

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 January 24, 2008, 10:48 Velocity fluctuation distribution near a wall #1 Matthieu Guest   Posts: n/a Hello, I am using Fluent 3d for simulating the trajectories of particles in a detention tank. The particles are assumed to be a discrete phase in a turbulent water flow. So, I am using the Discrete Random Walk Model in order to take into the effect of the turbulence on the particle motion. Each eddy is defined by a Gaussian distributed random velocity fluctuation u', v', and w'. But near the bed, the velocity fluctuation is not Gaussian anymore (especially the vertical velocity) (because of bursts). So, I would like to define my own distributions for the velocity fluctuations near the bed. Does someone know how I can access these distributions and modify them in an User Defined Function ? I would like to keep the Gaussian distribution when the wall unit, y*, is superior to a threshold value, and use my own distributions when y* is inferior to this value. Does someone have another idea to model the influence of burst on particle motion ? Matthieu

June 3, 2021, 09:40
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Vincenzo Luci
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Quote:
 Originally Posted by Matthieu ;148020 Hello, I am using Fluent 3d for simulating the trajectories of particles in a detention tank. The particles are assumed to be a discrete phase in a turbulent water flow. So, I am using the Discrete Random Walk Model in order to take into the effect of the turbulence on the particle motion. Each eddy is defined by a Gaussian distributed random velocity fluctuation u', v', and w'. But near the bed, the velocity fluctuation is not Gaussian anymore (especially the vertical velocity) (because of bursts). So, I would like to define my own distributions for the velocity fluctuations near the bed. Does someone know how I can access these distributions and modify them in an User Defined Function ? I would like to keep the Gaussian distribution when the wall unit, y*, is superior to a threshold value, and use my own distributions when y* is inferior to this value. Does someone have another idea to model the influence of burst on particle motion ? Matthieu
Hello Matthieu, I know this topic is old but have you solved this problem?