Parameters for moderate Re flow

[nipinl]

Hi all,
My aim is to simulate flow through a gyroid unit cell with Re 1 to 100. Geometry is similar to resolvedRock3d, but less complex. Hence I adapted resolvedRock3d example. Here is how I do:
For a fixed Resolution(N) 100, I run several combinations (within stability limit) of lattice velocity(u*) and tau with a pressure difference (dp). I calculate Re using the resulting average x velocity. For each combination, there is an upper limit of dp above which simulation diverges (gives nan).

I repeated the same with N = 256 and 500. However, I am unable to attain Reynolds number above 14. Simulation diverges at lesser values of dp for a higher N giving low Re. I’ve referred Kruger et al. chapter 7 for setting parameters and kept those under stable limits. ( Like u*<=0.1 , 0.8<= tau < 0.56, Ma < 0.17, deltaRho*/Rho* < 0.02).

Any suggestion on improving parameter set for higher Re?

[sfraniatte]

Hi,

I have two questions. Do you use Bouzidi boundary condition ? What is the physical duration of your simulation at Re=14 ? I had maybe the same issue of stability and I figured out that Bouzidi boundary condition is the problem. I can not explain why but, when I set dp condition, it does not work with Bouzidi. I hope that someone knows why and it will help you.

Best regards
Sylvain

[nipinl]

Hi Sylvain,

I use simple bounce back, same as in resolvedRock3d. I run 100s physical time. Did you face stability issues with bounce back? I tried to increase the Re for resolvedRock3d, but it it also showing similar behavior. I guess something I’m missing. The table of parameters I used and the case set-up is here:
https://www.dropbox.com/scl/fi/tjh2til3vug2isxg4kgue/highReA5.zip?rlkey=o0b2y03z3j079j9dqc79bun38&st=5x80bsa6&dl=0

Best Regards,
Nipin

[jan]

Hello all,

if you believe that bounce back might be the cause, then I’d suggest to try another boundary condition, see examples/laminar/poiseuille2d for a few options and to compare them.

@nipinl it’s great that you already considered the stable limits for the parameters. When you consult the paraview output, can you identify where the problem originates? For example some corner cell or at the inlet or outlet? Another example: If you have the inlet or outlet right next to a “wall” cell, then perhaps this causes problems.

In general I suggest the following:
– Where is the origin? Is there some pulsing? (then consider increasing the startup time or the simulated physical time frame) Is it located at a certain location in the geometry? Etc.
– Check the geometry, are the material numbers as you expect them? Are there any areas with potential conflict (like the example I gave above)?

Once we know a little more details, perhaps we can find the underlying problem easier.

Best regards,
Jan

[nipinl]

Hello Jan,
Thank you for the detailed response and for your insightful suggestions. I’ll follow those and keep you posetd.

Best,
Nipin

[Author]

Posts