Hello users!
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.
https://vsuxkw-db3pap001.files.1drv.com/y4mYym2yv7HMxzWgvv6UjA-46B_KvHFnMv6gxngsjB0Sh6vuMYovnWAPERQeFYbQGC8V6I7uNwwEG4-g4N35xV_sOq8HzHW9ZuRamASCT-UDEdUFvnJEfAns0wCiFGlYu4SLHSPryNyU4sxkEA5UJcuDcgmJNZFJdOlkBDNbwQ_p1q6B8adWg3Zqvlv6kbFb0RbbxI6_HeVycXZNVi8oGDH0Q?width=673&height=598&cropmode=none
However, it also gives artificial velocities in the xy-plane.
https://xcuxkw-db3pap001.files.1drv.com/y4m5iIhvcwdX-lLVul32IVmc9GZXLEUGgJLtFWaBCjg0GRs5rf9pjLwfMVxBwq8poiO7PedafZm7JwC7lW27o16ZjaNS5y_T3K9XxpKh32g4CCK8A71BoAWnESuaCImLgpFJSgUopBCaEdhZpPg_bzPKhL9DAt7J7XFuXgnTl7CHP1BYXt1cbNol9bPipotfA2XJakJ0Wj9GB8xHb5ZTD0wug?width=673&height=598&cropmode=none
The density variations are on the same order as the artificial velocity, and the streamlines show the closed circulations in the plane.
https://wcuxkw-db3pap001.files.1drv.com/y4mOb2ymziBvgwmOZ1uWMy7Rwurv8ySN4eDOPGI8idflhgYzXak9WAXtrFkegrbRW1495rYOi8mn22wMZ2PJcMPaSO1zAjUeQE660nK1JOdujXsyAcwPFD35z4F6fAt7M9gNp0bMT_hIOniozv1J6UuMT1YwKSYe6zbH6hC2e2nA0h0du4RaxuCHw5VRpakAG-LX6J4-Bp7lwUEgU3aqcad4A?width=673&height=598&cropmode=none
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
Regards,
Ivars