Pouseuille flow - velocity normal to boundary

I’m running a 2d pouseuille flow simulation using periodic boundary conditions along the channel, and BB conditions at the walls. The body force suggested by guo is being used to drive the flow. I noticed that I am getting velocities being generated normal to the boundary. Originally I thought this was caused by rounding error as they eminate from the boundary with a magnitude of around 1e-14 at the first few time steps, but after around 1000 timesteps they are at the order 1e-8, so i’m not sure whether this is the case. I am using a D2Q9 lattice, with the original (not incompressible) equilibrium distribution.
Has anyone else seen something similar to this? Any help would be greatly appreciated.


I am pretty convinced that your periodicity is not working perfectly. Have you tracked the total fluid mass in your system? I bet that it is decreasing. The reason could be that you are “missing” some wall nodes where the fluid is leaking or your populations are not correctly translated to the other end of the simulation box when they cross the periodic boundary.


i’m doing the same using lb2d_prime and tecplot.

If you need to store the simulation results in tecplot format,
Use the source files posted in the Research BB in “CFDlab in Kgu

Good luck