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Turbulent Length Scale and Intensity for Airfoil

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Old   April 5, 2011, 10:01
Default Turbulent Length Scale and Intensity for Airfoil
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Shamim Islam
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Hello All,

I am running a simulation of 3D wing (NACA 2412) of chord length 1m and span 0.3m in STAR CCM 4.04. I am using Spalart-Allmaras model. Now, I am in great trouble on setting the value of Turbulent Length Scale and Intensity. I am not getting any clue how to set the value of this parameter.

Anybody can help me- how can I set the value of Turbulent Length Scale and Intensity? I highly appreciate your suggestions.

Shamim
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Old   August 2, 2011, 07:47
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Hi Shamim,

Let me say that the wing you are on to is very interesting. Due to its very low aspect ratio the tip-vortex will dominate the entire flow which is essentially very hard to investigate.

However if you would like to calculate lift and drag, you can google some NACA papers and find some focused on determining 3D characteristics of an airfoil from 2D characteristics. As input, you can find easily 2D characteristics of 2412 or calculate via CFD.

I think turbulence length scale and intensity are should be thought secondarily. While simulating the flow around an airfoil, those parameters are applied to the boundary conditions, especially to the free-stream. For a such flow, turbulence intensity can be taken between %1 and %5. Turbulence length scale isn't very easy to determine but initially you can accept it 10 or 25 percent of the wing chord.
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Old   July 12, 2017, 23:11
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Joseph O'Neill
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Hi all!

I would like to possibly revive this thread as I am having a similar issue with both turbulent length scale and intensity.

I am running a relatively low Reynolds Number of 300,000 over a NACA 4318 airfoil with undulations along it's surface.

I have read that intensity can be estimated between 1 and 5 percent as husker has stated; however, the simulations for which I am running are mainly 2D. In this case the span of the wing is infinitesimally small as in my 2D simulation my dimensions run along the chord and thickness of the airfoil itself. How would one then determine the length scale for a 2D simulation? Would the same rationale as using 10-25% of the span length apply?

Thank you!

Joe

Edit: I forgot to mention that my chord length is 0.201786 meters with a domain that is 1c in front of the airfoil, 4c behind the airfoil, and 5c above and below the airfoil.
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