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

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 January 26, 2019, 19:25 How to calculate fluctuating velocity and turbulence intensity in RANS (OF) #1 New Member   Purn Prakash Join Date: Nov 2018 Posts: 27 Blog Entries: 1 Rep Power: 7 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. Last edited by purnp2; January 27, 2019 at 19:40. Reason: Better way of asking:

 February 8, 2019, 05:42 #2 Senior Member   Zander Meiring Join Date: Jul 2018 Posts: 125 Rep Power: 7 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 purnp2 and qutadah.r like this.

 September 20, 2020, 21:49 #3 New Member   Ashutosh Join Date: Apr 2020 Posts: 2 Rep Power: 0 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

 September 22, 2020, 08:06 #4 New Member   Pedro Pacheco Join Date: Dec 2019 Location: Portugal Posts: 10 Rep Power: 6 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. as13031996@ and qutadah.r like this.

 April 11, 2022, 12:47 #5 New Member   Pedro Pacheco Join Date: Dec 2019 Location: Portugal Posts: 10 Rep Power: 6 As a matter of fact my previous post does not apply to RANS results... Only for LES results, where U - Umean is the resolved part of the velocity fluctuations. I apologize if I misled anyone! lourencosm likes this.

 Tags flat plate, fluctuating velocity, turbulent intensity