Multigrid cycles and numerical scheme

Nkl · January 14, 2014, 17:24

I have assigned face sizings, each with element size of 0.01 m. The inflation option is total thickness with 15 layers, 1.7 growth rate and a maximum thickness of 0.004 m. With orthogonal quality I have an average of 0.85. I used these settings because with the other model I achieved values of yplus lower than 100.
I have tried to increase both element size and growth rate, but yplus did not change. Should I try mesh adaptation?

ghorrocks · January 14, 2014, 17:27

But did you look at the mesh you generated?

My comment on mesh sensitivity applies to the whole mesh, not just the inflation layers. For more details see the FAQ http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F and this is an excellent description of what to do http://journaltool.asme.org/Template...umAccuracy.pdf

Nkl · January 14, 2014, 17:46

What does it mean exactly "have take a look at your mesh?". From the beginning of my simulations I have changed advection scheme from high resolution to upwind, turbulence model from k-epsilon to SST, boundary condition type from outlet to opening in order to achieve convergence. I don't understand why with the other model I have good results with the same parameters. I will try to change other parameters. Thanks for all the help!

ghorrocks · January 14, 2014, 18:05

I mean use the post processor to look at the mesh and see its quality and size. Especially compare the two simulations which you report are giving different results despite similar setups.

Also be careful of using upwind differencing. You are going to struggle to get accurate answers with that.

January 14, 2014, 17:24		#1
Nkl Member Nikola Join Date: Sep 2013 Location: Madrid, Spain Posts: 60 Rep Power: 12	I have assigned face sizings, each with element size of 0.01 m. The inflation option is total thickness with 15 layers, 1.7 growth rate and a maximum thickness of 0.004 m. With orthogonal quality I have an average of 0.85. I used these settings because with the other model I achieved values of yplus lower than 100. I have tried to increase both element size and growth rate, but yplus did not change. Should I try mesh adaptation?

January 14, 2014, 17:27		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,729 Rep Power: 143	But did you look at the mesh you generated? My comment on mesh sensitivity applies to the whole mesh, not just the inflation layers. For more details see the FAQ http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F and this is an excellent description of what to do http://journaltool.asme.org/Template...umAccuracy.pdf

January 14, 2014, 17:46		#3
Nkl Member Nikola Join Date: Sep 2013 Location: Madrid, Spain Posts: 60 Rep Power: 12	What does it mean exactly "have take a look at your mesh?". From the beginning of my simulations I have changed advection scheme from high resolution to upwind, turbulence model from k-epsilon to SST, boundary condition type from outlet to opening in order to achieve convergence. I don't understand why with the other model I have good results with the same parameters. I will try to change other parameters. Thanks for all the help!

January 14, 2014, 18:05		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,729 Rep Power: 143	I mean use the post processor to look at the mesh and see its quality and size. Especially compare the two simulations which you report are giving different results despite similar setups. Also be careful of using upwind differencing. You are going to struggle to get accurate answers with that.