OpenLB – Open Source Lattice Boltzmann Code Forums on Lattice Boltzmann Methods General Topics Beginners Aid needed – Boundary Conditions

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• #1749
jieeshtker
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Hi folks,rnrnI am trying to set up a LB-simulation to simulate a pipe flow and I am experiencing several problems. I hope, you can help me in an understandable (not heavy formula using) way.rnrnFirst and most important question set:rnWhat should I do with any walls? I understand there are a lot of different approaches (bouncing back, inamuro, free slip, no slip, complex things, …) – but I fail programming any of these. As far as I understand, for a simple pipe flow I need a bouncing back condition.rnrnIs this still right?rnrnIf so, all I have to do is to take the distribution functions pointing towards the wall (e.g. pointing North, Northeast, Northwest) and put them into the wall (South, Southeast, Southwest). [This ought to be free slip or what it is called.] Now, if I switch east and west I should have no-slip.rnrnIs this still right?rnrnAnd then, what do I do if an obstacle is to be simulated? There could be corners of which I have absolutely no clue what to do with them.rnrnrnrnTo the not critical questions:rnrnIs there any way to set boundary conditions by defining macroscopic parameters (e.g. von Neumann, Dirichlet)?rnrnrnIs there a way, to realize different viscosities? I think, viscosity is only used in the collision, but can I just use different (and chaning) viscosities in a single cell (and keep conservation of mass)?rnrnMany thanks for your time and answers.

#2133
mathias
Keymaster
Quote:
Quote from jieeshtker on January 7, 2014, 10:13rnHi folks,rnrnI am trying to set up a LB-simulation to simulate a pipe flow and I am experiencing several problems. I hope, you can help me in an understandable (not heavy formula using) way.rnrnFirst and most important question set:rnWhat should I do with any walls? I understand there are a lot of different approaches (bouncing back, inamuro, free slip, no slip, complex things, …) – but I fail programming any of these. As far as I understand, for a simple pipe flow I need a bouncing back condition.rnrnIs this still right? rn>>Yes, thats right. Have a look at our example code.rnrnIf so, all I have to do is to take the distribution functions pointing towards the wall (e.g. pointing North, Northeast, Northwest) and put them into the wall (South, Southeast, Southwest). [This ought to be free slip or what it is called.] Now, if I switch east and west I should have no-slip.rnrnIs this still right? rn>>Yes, thats right again. You may have a look in the standard literature, e.g. Sukop’s book “”Lattice Boltzmann Modelling””.rnrnAnd then, what do I do if an obstacle is to be simulated? There could be corners of which I have absolutely no clue what to do with them.rn>> You can also use bounce back or an interpolation sheme like those of Bouzidi. Have also a look at our 3d example “”cylinder3d”” where we use the later one.rnrnrnTo the not critical questions:rnrnIs there any way to set boundary conditions by defining macroscopic parameters (e.g. von Neumann, Dirichlet)? rn>> Yes, there are may scheme. You may have a look in the standard literature, e.g. Sukop’s book “”Lattice Boltzmann Modelling””. rnrnrnIs there a way, to realize different viscosities? I think, viscosity is only used in the collision, but can I just use different (and chaning) viscosities in a single cell (and keep conservation of mass)?rn>> You can set it different for any cell for the collision step. However, it may not make sence physically.rnrnMany thanks for your time and answers.
#2134
mathias
Keymaster

See the quotes.rnMathias

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