how find fluctuating velocity

Far · June 25, 2012, 01:12

Thats secret behind success of eddy viscosity turbulence models for many types of engineering flows to find out mean engineering quantities. Thanks.

Far · June 25, 2012, 01:21

Once the equation are averaged over time and space (ensemble average, please correct me, if it wrong). then I find two situations very interesting.

1. We are trying to find out the fluctuating components through RSM model. In this case it is only giving you only the RSM values of them instead of true turbulence. Well I admit that RANS only model the large eddies.

2. Running the unsteady simulation to find out the transient solution from the averaged qualities.

I also find it out it very confusing situation that when we make the Reynolds averaging, we get the NS in terms of mean quantities except Reynolds stresses.
Then to find out these components, we need to express them in terms of mean quantities. Whats the point?

PS. May be I am confusing the concepts. So this may be the good chance that I get corrected by some expert.

ghorrocks · December 16, 2016, 05:23

Doesn't the post you quoted show you how to do it?

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June 25, 2012, 01:12		#21
Far Senior Member Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,558 Blog Entries: 6 Rep Power: 54	Thats secret behind success of eddy viscosity turbulence models for many types of engineering flows to find out mean engineering quantities. Thanks.

June 25, 2012, 01:21		#22
Far Senior Member Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,558 Blog Entries: 6 Rep Power: 54	Once the equation are averaged over time and space (ensemble average, please correct me, if it wrong). then I find two situations very interesting. 1. We are trying to find out the fluctuating components through RSM model. In this case it is only giving you only the RSM values of them instead of true turbulence. Well I admit that RANS only model the large eddies. 2. Running the unsteady simulation to find out the transient solution from the averaged qualities. I also find it out it very confusing situation that when we make the Reynolds averaging, we get the NS in terms of mean quantities except Reynolds stresses. Then to find out these components, we need to express them in terms of mean quantities. Whats the point? PS. May be I am confusing the concepts. So this may be the good chance that I get corrected by some expert.

December 16, 2016, 05:23		#23
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	Doesn't the post you quoted show you how to do it?