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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%

 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.