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-   -   How to calculate fluctuating velocity and turbulence intensity in RANS (OF) (https://www.cfd-online.com/Forums/openfoam-post-processing/214295-how-calculate-fluctuating-velocity-turbulence-intensity-rans.html)

 purnp2 January 26, 2019 20:25

How to calculate fluctuating velocity and turbulence intensity in RANS (OF)

Hello, senior Fomers. :)

I am new to CFD field and currently, I am doing a simulation of T3A tutorial case which uses kOmegaSSTLM model.

I have to calculate turbulent intensity and plot it on a graph along a line very close to the flat plate surface.

I used the postProcessing tool named "turbulenceIntensity" and plotted a graph along a line which I drew along the flat-plate-wall. The problem is I am getting a very weird graph.
The image should be here:

Can you please tell me where I am making mistake?

(((BTW, I want to also know what are the three columns in U file represent?)))

Thank you very much.

 yambanshee February 8, 2019 06:42

the three columns in the U file represents the x, y and z components of velocity. I'm not sure what you mean by the fluctuating velocity, but if you're talking about turbulent velocity fluctuations (u') then you won't be able to model that with RANS equations, as their whole purpose is to remove the fluctuating component and average it out

 as13031996@ September 20, 2020 22:49

Hello friend i saw discussion it's true with rans model we cannot calculate u'instantenous sir if am using LES model and i have umean and uprime2mean how can i find value of u' instantaneous velocity

 ptpacheco September 22, 2020 09:06

Hello Ashutosh,

According to Reynolds decomposition:

U = Umean + U'

So all you have to do is subtract from the U(x,y,z,) field the Umean(x,y,z). In paraView, for example, you can do this by setting a Calculator filter.

Hope this helps.

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