I am currently having a problem where the solution converges to a steady-state, but artificial velocities have been generated in the cross-section of the 3D channel. There should be no flow in that plane.
The geometry is 34 x 34 x 3.
The walls are no slip for velocity.
The force is applied in z-direction: F=(0,0,Fz)
The Neumann condition of zero is used in the flow direction (df/dz=0) making it really a 2D case.
It gives the exact (err<1%) velocity profile as compared to the analytical solution.
However, it also gives artificial velocities in the xy-plane.
The density variations are on the same order as the artificial velocity, and the streamlines show the closed circulations in the plane.
The artificial velocities are proportional to the force squared: velocities ~ force[sup]2[/sup].
They are linearly proportional to the viscosity: velocities ~ viscosity.
They are proportional to the grid size cubed: velocities ~ channel width[sup]3[/sup].
I have tried two collision schemes: SRT and TRT.
I have tried two forcing schemes: He-Shan-Doolen and Luo’s.
I have tried two boundary condition methods: bounce-back, half-way bounce-back.
All the combinations give me the artificial velocities!
The questions are:
If you replicated the problem, would you also get those artificial velocities?
Where are they coming from?
Can I get rid of them?
If yes, How to get rid of them?
I hope somebody can clear this mystery for me