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littlelz September 3, 2008 11:37

decay of turbulence intensity
 
I am doing the transition modelling in CFX, and i got the info on turbulence intensity decay from the inlet to leading edge. I am trying to estimate it, and then I found the equation in CFX manual is not correct? any one have ever tried it? please give me some idea on it? thanks in advance.

The reason I try this is I am doing transition modeling on simple flat plate. I get over-predicted Rex number and I think it may because the turbulence intensity is too low around leading edge area (I checked it, it is about 0.045%). the inlet intensity I st is 10%, So I want to estimate the inlet intensity from prescribed intensity.

another question is as I checked the turbulence intensity from the result and I found the value on inlet boundary is 1% rather 10%, is that all right? Is it supposed to be the initial value 10%

thanks for your any idea!

John S. September 3, 2008 12:43

Re: decay of turbulence intensity
 
What's the viscosity ratio at your inlet? If it's really high (>100) wallshear can dominate the near-wall flow and cause the turbulence intensity to decay rapidly. If it is high you can try specifying values for intensity (.10 for 10%) and viscosity ratio (should be ~1-10 at the inlet).

littlelz September 4, 2008 05:49

Re: decay of turbulence intensity
 
in my case, intensity is 10%, and viscosity ratio is 10. But my inlet is really far from the leading edge (15 times of length of flat plate). I think that will cause great decay of the inlet intensity. So I want to estimate the inlet intensity using the prescribed value in leading edge area, but I found the equation in CFX manual is not correct, it is not a decay formular but a increment one.

thanks for your reply

guxin7005 May 16, 2014 16:44

Hi, littlelz

I met the same question you have in CFX. I draw several lines from the inlet to leading edge, sometimes the turbulence intensity decay, sometimes it increase. However, in FLUENT,those lines have the same the turbulence intensity distribution from inlet to leading edge.

How did you solve it in the end?


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