residuals behaviour on steady state simulations

c120613 · October 18, 2011, 21:47

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

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.

October 18, 2011, 21:47	residuals behaviour on steady state simulations	#1
c120613 Member Domenico Join Date: Sep 2009 Location: Cranfield Posts: 48 Rep Power: 16	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!

October 20, 2011, 09:25	discussion	#5
c120613 Member Domenico Join Date: Sep 2009 Location: Cranfield Posts: 48 Rep Power: 16	Guys, for this discussion can we contact privately please. My email address is: d.dicugno@yahoo.com Cheers

October 20, 2011, 17:20		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	I do not discuss forum questions by email or private messaging. bhatiadinesh likes this.

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October 19, 2011, 05:41		#2
Far Super Moderator Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,553 Blog Entries: 6 Rep Power: 54	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?

October 19, 2011, 05:43		#3
Far Super Moderator Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,553 Blog Entries: 6 Rep Power: 54	Last but not the least : pls always try to put the some pics of mesh, goemtry, residual plot

October 19, 2011, 06:43		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	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.