physical velocity and reference velocity

Lattice Boltzmann Method LBM: Theory
#1

Hello
I have small question about the way how to calculate physical velocity from LBM results.
Namely, I used for this such a equation (the same which is used before LBM experiment to calculate dt_{psyh})
dt_{psyh} = u_{lb} * dx_{psyh} / u_{psyh}

But the problem appears when:

  • in one experiment I take as a reference velocity 2 (maximum velocity based in Poiseuille eq.)

  • and from LBM experiment I receive maximum lattice velocity 1.5

  • in second experiment I take as a reference velocity 1 (mean velocity based on Poiseuille eq.)

  • and from LBM experiment I receive maximum lattice velocity 0.74999

Taking into the account above equation it seems that in first example we receive 2 times quicker flow.

So,
I read in many places that this is only the reference velocity and the results should be the same (for example on this forum)
or
Does it mean that I calculate the u_{phys} in a wrong way?

Thanks for any help

#2

Hi kjurczuk
which parameter did you change In each simulation ? Notice that you have limitation to choose u_lb beacause mach number Ma=u_lb/cs shoul be in order 0.1.
By the way I have sent a private massege for you, have a look.

#3

Hello
Thanks for reply.
The problem was solved.
I had small mistake during ‘nu’ calculation.

#4

Hi
That 's OK. please check your private message. I have asked some other question to know and i will be glad if you reply.
Thanks

#5

Hello
Can You send it once again because I have not received any:)
Sorry that I write there about this, but Your mail is hidden.