Sudden pressure change in first time step

  • 33 Views
  • Last Post 14 May 2020
mskr posted this 01 May 2020

I have a simple pipe case with an obstacle in the middle:

I let liquid water flow through it, in transient sim, with the following inlet condition:

The outlet is just the default (pressure=0).

Why am I getting this sudden pressure jump in first time step?

And why is the pressure not uniform at the beginning, but has this linear gradient from low at inlet to high at outlet?

t = 0 s

t = 0.01 s

Order By: Standard | Newest | Votes
rahkumar posted this 05 May 2020

Hello,

What is your mesh quality?

Regards, Rahul

mskr posted this 05 May 2020

It is just a simple test case. Here is a screenshot of the mesh quality color coding from Mechanical. I think it has good orthogonality and skewness, but is of course way too coarse for anything meaningful.

Thanks for the response. But in the meantime I was just moving along assuming this is normal behavior for the boundary conditions and time step I specified.

rahkumar posted this 06 May 2020

What type of initialization have you used? 

Regards, Rahul

mskr posted this 06 May 2020

abenhadj posted this 07 May 2020

Can you try with a better mesh and use pride layers to resolve the boundaries

Best regards, Amine

abenhadj posted this 07 May 2020

and on yur current mesh initialize with zero velocity and use conservative time step at first.

Best regards, Amine

mskr posted this 14 May 2020

Ok I initialized everything with zero velocity. I was already using fixed time step 0.01 sec. Is fixed the same as conservative?

Anyway the results are similar.

t = 0 s

t = 0.01 s

I have also added inflation layers. Are they the same as pride layers?

Sorry but I wasn't able to achieve really good mesh quality, especially in the middle region.

The pressure jump is also visible with time step of 1e-05 s.

rahkumar posted this 14 May 2020

Hello, 

What is the solution method you using?

 

Regards, Rahul

Close