turbulence model?

jai · April 25, 2011, 08:00

hi,

i'm simulating centrifugal compressor, which's rotating at 100,000rpm.
which turbulence model is better for this?
can i use k-E model (with y+ is 10-20) for this? some people recommended to use sst but for sst-model is y+ < 2. it difficult to maintain this y+ on all region.
please help me to understand and choose.
thanks.

juliom · April 25, 2011, 08:51

you should not use K-E model, since you will have a complex fluid flow distribution, if you read more about K-E model you will find that this model does not suit for this application since you will have rotation and swirl. I suggest you to use RSM

ghorrocks · April 26, 2011, 21:59

Quote:

I suggest you to use RSM

This is unlikely to be any more accurate than the 2 equation models, and will definitely be a lot harder to converge.

The best default option is the SST model. Only change away from this model when you have a good reason to do so. SST works fine with y+ in the wall function region (ie >11), so SST does not demand a y+<2 mesh.

juliom · April 27, 2011, 08:53

I agree with you about the two model equation, they are the most efficient when the computational resource is low. However we have to take into consideration several condition when they are used.
One of the most important is when there is swirl, like is this case, due to the fact that is a turbumachine, you have to make some proves with the turbulence models, starting with the two equation until RMS. No doubt RMS is the most complex and you need a lot of computational resource, this is the worst part.
FLUENT has several information about it, and from my point of view they explain in more details the topics.
Yours sincerely
JM

stumpy · April 27, 2011, 09:35

If swirl is important then use SST and enable the Curvature Correction option. This should give something closer to a RSM solution in swirl regions, but retaining the benefits of the wall treatment with the SST model.

ghorrocks · April 27, 2011, 19:29

In my experience for many flows RSM does not give results any more accurate than a two equation model, even though many two equation models do not include curvature effects.

That is why I recommend SST as a starting point, and enable curvature correction as Stumpy suggests. I would be surprised if an RSM model proves to be more accurate than this, even though RSM models contain "more physics".

jai · April 27, 2011, 23:50

As you have suggested, tried RSM model and the convergence is poor.
So decided to go about with the SST with curvature correction option.

Thanks for you suggestions.

April 25, 2011, 08:00	turbulence model?	#1
jai Member jaikrishna Join Date: Mar 2009 Location: chennai Posts: 56 Rep Power: 17	hi, i'm simulating centrifugal compressor, which's rotating at 100,000rpm. which turbulence model is better for this? can i use k-E model (with y+ is 10-20) for this? some people recommended to use sst but for sst-model is y+ < 2. it difficult to maintain this y+ on all region. please help me to understand and choose. thanks.

April 27, 2011, 23:50	RE:	#7
jai Member jaikrishna Join Date: Mar 2009 Location: chennai Posts: 56 Rep Power: 17	As you have suggested, tried RSM model and the convergence is poor. So decided to go about with the SST with curvature correction option. Thanks for you suggestions.

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April 25, 2011, 08:51		#2
juliom Senior Member Julio Mendez Join Date: Apr 2009 Location: Fairburn, GA. USA Posts: 290 Rep Power: 18	you should not use K-E model, since you will have a complex fluid flow distribution, if you read more about K-E model you will find that this model does not suit for this application since you will have rotation and swirl. I suggest you to use RSM

April 27, 2011, 08:53		#4
juliom Senior Member Julio Mendez Join Date: Apr 2009 Location: Fairburn, GA. USA Posts: 290 Rep Power: 18	I agree with you about the two model equation, they are the most efficient when the computational resource is low. However we have to take into consideration several condition when they are used. One of the most important is when there is swirl, like is this case, due to the fact that is a turbumachine, you have to make some proves with the turbulence models, starting with the two equation until RMS. No doubt RMS is the most complex and you need a lot of computational resource, this is the worst part. FLUENT has several information about it, and from my point of view they explain in more details the topics. Yours sincerely JM

April 27, 2011, 09:35		#5
stumpy Senior Member Join Date: Apr 2009 Posts: 531 Rep Power: 21	If swirl is important then use SST and enable the Curvature Correction option. This should give something closer to a RSM solution in swirl regions, but retaining the benefits of the wall treatment with the SST model.

April 27, 2011, 19:29		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	In my experience for many flows RSM does not give results any more accurate than a two equation model, even though many two equation models do not include curvature effects. That is why I recommend SST as a starting point, and enable curvature correction as Stumpy suggests. I would be surprised if an RSM model proves to be more accurate than this, even though RSM models contain "more physics".