[ari003]

Hello Foamers,
I was trying to run the LES channel395 with Ubar=10.5 instead of 0.1355 which was the default. Whenever I do so I'm getting very unexpected result and its obvious because I kept the 0 folder unchanged where the U field had non-uniform list initialization with velocities around 0.1335.

internalField nonuniform List<vector>
60000
(
(0.0107927 -2.64614e-05 0.00214946)
(0.0107939 -3.50395e-05 0.0018715)
(0.010668 -2.59457e-05 0.0018284)
..........
.......

I can remove the initialization but it will take a long time to get a developed flow, so in this regard I'm trying to initialize the field with velocity around 10.5( Ubar=10.5) instead of 0.1335. If anyone is having any idea on this it will be my pleasure if you share so.

[Tobermory]

Can you share more details of the problem? You say that you are getting a "very unexpected result" ... what exactly are you seeing?

And let me just check - you want to set up a turbulent field with a Ubar of around 10m/s, you're starting with a velocity field in folder 0 with Ubar~0.1m/s, and you're using meanVelocityForce in fvOptions to control Ubar?

If this is the case, then the velocity field has to be accelerated by a factor of 100, which is pretty large. Are you applying relaxation to meanVelocityForce? Have you considered scaling the initial velocity field, or increasing Ubar in stages? Is your mesh still appropriate for this 100x Re number flow?

Either way, to understand your problem, my friend, you'll need to share some more details.

[ari003]

Can you share more details of the problem? You say that you are getting a "very unexpected result" ... what exactly are you seeing?

When I check the TI plot along the streamwise direction it was not something which I expected from my knowledge perspective and this I can imagine because of discrepancy between initialized field and Ubar. After researching I found that the true turbulent field in the domain can be observed if I run the simulation for long time until the initial field is totally disregarded.

And let me just check - you want to set up a turbulent field with a Ubar of around 10m/s, you're starting with a velocity field in folder 0 with Ubar~0.1m/s, and you're using meanVelocityForce in fvOptions to control Ubar?

Yes. If I use some uniform field to initialize, that might lead to high dissipation error and long transient time.

If this is the case, then the velocity field has to be accelerated by a factor of 100, which is pretty large. Are you applying relaxation to meanVelocityForce? Have you considered scaling the initial velocity field, or increasing Ubar in stages? Is your mesh still appropriate for this 100x Re number flow?

I finally decided to use the scale up option for the initialized field like C=10.5/0.1335 this I ll use as a multiplication factor.

[Tobermory]

Yes, it will take a few eddy turnover times (H/u_tau) for the turbulence to adjust to the new conditions, maybe longer for such a large perturbation.

Agreed on the necessity for taking a short cut - the spin-up time can be pretty long, otherwise.

[ari003]

Thanks a lot for your kind response to my problems.
Have a nice weekend.