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-   -   residuals behaviour on steady state simulations (http://www.cfd-online.com/Forums/cfx/93550-residuals-behaviour-steady-state-simulations.html)

c120613 October 18, 2011 21:47

residuals behaviour on steady state simulations
 
Dear All,

I was running a simulation with a coarse mesh at the boundary layer such that the value of y plus was about 1000 and I used the SST turbulence model. Of course this is wrong and then I moved to refine the mesh at the boundary layer in order to decrease the y plus towards 1. By doing this operation I noticed that the residuals of the mass and momentum conservation presented a higher frequency and amplitude of oscillation with the iteration number.

Does someone knows what is going on??

The simulated system consists in an intake coupled with a fan. If you need to know more details, please let me know.

Thank you in advance!

Far October 19, 2011 05:41

1. May be the problem is transient, which was not shown in the coarse mesh.

2. are you modeling complete intake and fan or somoe sector?

3. pls write down Over all mesh size and aspect ratio?.

4. Also give details of time scale, like time step size, auto or physcial time scale?

Far October 19, 2011 05:43

Last but not the least : pls always try to put the some pics of mesh, goemtry, residual plot

ghorrocks October 19, 2011 06:43

And a large y+ is not necessarily wrong, and y+=1 is not necessarily right. Do a sensitivity study to find out what near wall spacing you need.

But if you are doing a turbomachinery application you almost certainly need a small y+, but it could be much larger than 1.

c120613 October 20, 2011 09:25

discussion
 
Guys, for this discussion can we contact privately please. My email address is: d.dicugno@yahoo.com

Cheers

ghorrocks October 20, 2011 17:20

I do not discuss forum questions by email or private messaging.


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