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Lagrangian particle tracking of laminar mixing

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Old   January 22, 2017, 15:48
Question Lagrangian particle tracking of laminar mixing
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Robert
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Hi,

I am almost starting my work about lagrangian particle tracking in a laminar stirred tank. I will do this in Fluent using the Discrete Phase Model (DPM). However, my question does not neccessarily concern Fluent only. I was wondering about a fundamental mixing question: How do I achieve mixing? Let me explain a little more. In turbulent regime, randomness is readily induced by the fluctuating velocities caused by the eddies, resulting in mixing. However, my system is laminar. In my understanding, this means that particles starting at the same place will follow the exact same path, thus ending up on the same place. The mechanism differentiating between paths of particles starting at the same place is diffusion. However, this is not generally induced in a lagrangian model. Can anybody please explain to me how the lagrangian treatment of particles can result in mixing in laminar flow regime?

Thank you
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Old   January 22, 2017, 16:30
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Filippo Maria Denaro
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The underlying hypothesis under the lagrangian tracking is that the particle has a constant property alongh its path line, that is DY/Dt=0. This way you just follow the particle by solving dx/dt = v. That framework in which there is no diffusion of a property does not depend on the laminar or turbulent regime of the flow. Thus, we can focus on the mixing due to the convection. The mixing can be analysed by the way in which two close particles separate each others. Laminar unsteady flows can generate mixing. Turbulence can generate chaotic mixing.

For example https://en.wikipedia.org/wiki/Chaotic_mixing
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Old   January 30, 2017, 18:05
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Yasser
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Hi, I am using Fluent 6.3 for the modeling of gas-solid flow in a cyclone separator. The continuous phase modeling is steady. Is it a must to model the discrete particles as unsteady particle tracking? if so, what are the values I have to set for the particle time step size and the number of time steps? also what about the start and stop time for injection ? Actually the Fluent Help is not clarifying these points
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