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-   -   Question on Turbulence Intensity (http://www.cfd-online.com/Forums/fluent/48593-question-turbulence-intensity.html)

Eric June 24, 2008 11:48

Question on Turbulence Intensity
 
Dear all, I am really confused with the definition of turbulence intensity. In WIKI it is described as following: 1. High-turbulence case: High-speed flow inside complex geometries like heat-exchangers and flow inside rotating machinery (turbines and compressors). Typically the turbulence intensity is between 5% and 20%

2. Medium-turbulence case: Flow in not-so-complex devices like large pipes, ventilation flows etc. or low speed flows (low Reynolds number). Typically the turbulence intensity is between 1% and 5%

3. Low-turbulence case: Flow originating from a fluid that stands still, like external flow across cars, submarines and aircrafts. Very high-quality wind-tunnels can also reach really low turbulence levels. Typically the turbulence intensity is very low, well below 1%.

So according to what presented above, turbulence intensity increases with increasing velocity, for a pipe flow which means larger Renold number larger turbulence intensity. right? We know that, however, for a fully developed pipe flow the turbulence intensity at the core can be estimated as:

I = 0.16 *(Re_dh)^{-1/8} based on this equation, why a larger Re means smaller turbulence Intensity???

And what confuses me more is Fluent Report. After solution converged, when i report turbulence intensity by Area-Weighted Average, i got 400%!! How could it be??

Your help will be really appreciated.

Regards, Eric

GOPINATH87 March 7, 2012 05:30

Laminar flow at inlet and turbulence due to rotary motion of the impeller
 
How can I specify turbulent intensity for Re = 1400 at the inlet of stirred reactor operating at high rpm...

What happens if there is a Laminar flow at fluid inlet and turbulence due to rotary motion of the impeller (MRF method)


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