Wind load on surface => Turbulence modelling

pz1337 · March 7, 2012, 11:57

Hello,

i am trying to modell the load on surface by the wind, using
- power law for the inlet velocity
- sand grain roughness on the ground
- keps or kw-sst modell
in ansys cfx 14.0

Wind velocity are hitting the surface around 15m/s. I have pressure measurements from a wind tunnel - but they do not match.

Can you advise me on
(1) which turbulence model is better?
(2) how can i (iteratively) see how fine i have to resolve the mesh near the surface?

Thanks a lot in advance!

pz1337 · March 7, 2012, 12:09

i get a converged solution using kw sst and a first cell height of 0.01m on the surface. When I changed that to 0.005m (Using Inflation, First Cell height@0.005m, max Layers: 15, ratio 1.2 to achieve a smooth transition to the sorrounding area).

I get very bad convergence, osciallating at around 5e-4 (comparing to 1e-6) before.

any advice on this? I am sure there is a simple explanation.

Thanks again

ghorrocks · March 7, 2012, 18:02

Have you seen these FAQ:
http://www.cfd-online.com/Wiki/Ansys...gence_criteria

http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F

pz1337 · March 7, 2012, 18:07

Hi,

thank you - yes I have.

I am constantly working on the problem and was hoping for some suggestions to speed things up as I am working on the problem already for quite some time and each new calculation takes several hours.

March 7, 2012, 11:57	Wind load on surface => Turbulence modelling	#1
pz1337 New Member Merend Join Date: Jan 2011 Posts: 12 Rep Power: 15	Hello, i am trying to modell the load on surface by the wind, using - power law for the inlet velocity - sand grain roughness on the ground - keps or kw-sst modell in ansys cfx 14.0 Wind velocity are hitting the surface around 15m/s. I have pressure measurements from a wind tunnel - but they do not match. Can you advise me on (1) which turbulence model is better? (2) how can i (iteratively) see how fine i have to resolve the mesh near the surface? Thanks a lot in advance!

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March 7, 2012, 12:09		#2
pz1337 New Member Merend Join Date: Jan 2011 Posts: 12 Rep Power: 15	i get a converged solution using kw sst and a first cell height of 0.01m on the surface. When I changed that to 0.005m (Using Inflation, First Cell height@0.005m, max Layers: 15, ratio 1.2 to achieve a smooth transition to the sorrounding area). I get very bad convergence, osciallating at around 5e-4 (comparing to 1e-6) before. any advice on this? I am sure there is a simple explanation. Thanks again

March 7, 2012, 18:02		#3
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	Have you seen these FAQ: http://www.cfd-online.com/Wiki/Ansys...gence_criteria http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F

March 7, 2012, 18:07		#4
pz1337 New Member Merend Join Date: Jan 2011 Posts: 12 Rep Power: 15	Hi, thank you - yes I have. I am constantly working on the problem and was hoping for some suggestions to speed things up as I am working on the problem already for quite some time and each new calculation takes several hours.