In these pictures you can also find streamlines received based on the Navier-Stokes (N-S) flow simulation. Based on them we see vortexes.
However when I simulated flow in this geometry by LBM with comparable conditions to N-S calculations, I could not received any vortex, everywhere there was a laminar flow or something very similar.

Maybe somebody has any idea what I did bad ?
Maybe the LBM model was to simple ?
Maybe I forgot about something ?
Thanks for any help

Is your resolution high enough? You can only see vortices if you can resolve them.
Is the Reynolds number high enough? In or close to the Stokes regime, you usually do not observe vortices. You could try to reduce the viscosity and see what happens.
Have you waited long enough? It may also help to add some fluctuations at the beginning to “help” the flow to become unsteady.

Hello
Thank you very much Timm for response.
As you suggested I tried to find problem in many ways, below you can find summary:

I tried to increase resolution but I still was not able to see vortex.

2.What does it mean resolve vortexes? I thought that the model which I adapted in my simulation is enough to simulate steady flow and in the same time steady vortexes. (LBM D2Q9 model with BGK, constant pressure conditions at inputs/outputs (GUO2012 extrapolation method) and half bounce-back at walls.) Am I wrong ?

Currently I don’t want to consider unsteady vortexes.

I finish calculation when the “steady flow condition” is reached, i.e. differences between velocities in neighboring steps are smaller than 10e-6. Is it not enough ?

inlet diameter=8mm, water kinematic viscosity = 1,00E-06 m2/s
b) mean flow at inlet 005 cm/s: Re = 0.008 * 0.05 / 0.000001 = 400
c) mean flow at inlet 010 cm/s: Re = 0.008 * 0.10 / 0.000001 = 800
d) mean flow at inlet 022 cm/s: Re = 0.008 * 0.25 / 0.000001 = 2000
e) mean flow at inlet 045 cm/s: Re = 0.008 * 0.45 / 0.000001 = 3600
f) mean flow at inlet 115 cm/s: Re = 0.008 * 1.15 / 0.000001 = 9200
g) mean flow at inlet 250 cm/s: Re = 0.008 * 2.50 / 0.000001 = 20000

Hi Gustaw，
What is the relaxation time tau in your simulation? U will get comparable results to NS simulation when tau~1 and Mach number (u/c) ~0.01.
Best
Dongke

One response to Timm and dongke:
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To be sure that I calculated Reynolds number, Mach number etc well, I wrote shortly some of the experiment parameters and used equations:

I can increase tau, but it is hard. On the other side, Mach is quite good, isn’t it ?
lattice Reynolds number is also oddly high, did I calculate it well, hhmmm ?

I usually caculate the parameters as the following steps:

define the space step delta x.

define the time step delta t, and the relaxation time tau is determined accordingly.

check the Mach number is less than 0.1 or not; and tau is in the zone [1.0/1.99~2.0].

If Ma is higher than 0.1 and tau~0.5 (1/tau<=1.99 for SRT LBM), We can run LBM very well but can’t get good results as NS solver.

I think the Mach and 1/tau (1.995) is too high. I suggest making Ma ~ 0.01 and 1/tau ~ 1.85 as I have suggested earlier.
make:
(1) u_lb=0.001
and then:
(2) dt_ph = 0.00000011111 s.
(3) Ma = 0.0017.
(4) tau = 0.62 (1/tau = 1.61).

I usually caculate the parameters as the following
steps:

define the space step delta x.

define the time step delta t, and the
relaxation time tau is determined accordingly.

check the Mach number is less than 0.1 or not;
and tau is in the zone [1.0/1.99~2.0].

If Ma is higher than 0.1 and tau~0.5 (1/tau<=1.99
for SRT LBM), We can run LBM very well but can’t
get good results as NS solver.

I think the Mach and 1/tau (1.995) is too high. I
suggest making Ma ~ 0.01 and 1/tau ~ 1.85 as I
have suggested earlier.
make:
(1) u_lb=0.001
and then:
(2) dt_ph = 0.00000011111 s.
(3) Ma = 0.0017.
(4) tau = 0.62 (1/tau = 1.61).

Maybe it will work.
Hello dongke
I tried to do calculations as You proposed.
However, I do not know how You received
(4) tau = 0.62 (1/tau = 1.61).
for water kinematic viscosity equals about 0.000001 m^2/s
for your calculation kinematic visc = 0.001 m^/s

Gustaw
Maybe I made a mistake yesterday. Today, I will test the 2D problem by my code and show my results later.
Dongke

I have tested the problem by simulating the 2D cylinder flow.
The parameters (Real World) are :
1.0 ! density (density per node)
1.0E-6 ! dynamic viscocity
0.008 ! lengthx: physical length in x direction
500 ! Nx: total meshes in x direction
1.5 ! u_in: inlet velocity

And the LB parameters (LBM World) are:
u_in(LB) = 0.0100251
omega = 1.995
tau = 1.0/1.995
delta_x = 1.6e-005
delta_t = 1.06934e-007

Boundary conditions
topwall: outlet partial u_y / partial y =0
left and right walls: solid wall
bottom wall: inlet (u_x, u_y) = (0, u_in)

Gustaw
Maybe I made a mistake yesterday. Today, I will
test the 2D problem by my code and show my results
later.
Dongke

I have tested the problem by simulating the 2D
cylinder flow.
The parameters (Real World) are :
1.0 ! density (density per node)
1.0E-6 ! dynamic viscocity
0.008 ! lengthx: physical length in x direction
500 ! Nx: total meshes in x direction
1.5 ! u_in: inlet velocity

And the LB parameters (LBM World) are:
u_in(LB) = 0.0100251
omega = 1.995
tau = 1.0/1.995
delta_x = 1.6e-005
delta_t = 1.06934e-007

Boundary conditions
topwall: outlet partial u_y / partial y =0
left and right walls: solid wall
bottom wall: inlet (u_x, u_y) = (0, u_in)