CFD Online Discussion Forums

CFD Online Discussion Forums (https://www.cfd-online.com/Forums/)
-   OpenFOAM Post-Processing (https://www.cfd-online.com/Forums/openfoam-post-processing/)
-   -   Fluctuating component of a scalar quantity (https://www.cfd-online.com/Forums/openfoam-post-processing/219817-fluctuating-component-scalar-quantity.html)

elden August 9, 2019 13:59

Fluctuating component of a scalar quantity
 
Hi,
I'm dealing with external aerodynamics problems with dispersion of gaseous substances.
Simulations are carried out considering URANS and a Scale Adaptive approach for the turbulence model (kOmegaSSTSAS). The tracer gas is transported by means of the scalarTransport FO (i.e. as a passive scalar)

I'd like to postprocess not only the Reynolds Stress Tensor by means of the prime2Mean utility but also the turbulent diffusion flux of concentration : <u'*c'>; <v'*c'>; <w'*c'>
Related to the postProcess of these last three quantities I'm facing two problems:

- The first one is mainly conceptual and it's related to the fluctuating part of the velocity field. Since the turbulence model is the kOmegaSSTSAS, should I compute directly the fluctuations of the velocity field? Or should I consider the assumprtion made in the turbulenceIntensity FO (u'=v'=w') accounting for the fluctuating part as uPrime=sqrt(k*2/3)?
- The second is related to the code needed in order to evaluete the turbulence intensity of a scalar (c') and subsequently the turbulent diffusion fluxes (< u_i '*c' >). My intent was to somehow exploit the FO (fieldAverage.C/H and fieldAverageItem) used for prime2Mean computation but I got lost. I can't find the proper way to do that.

Thanks for reading.
Hoping to find some answers

elden September 9, 2019 12:15

possible answer to question number 2
 
Well,
I think I've menaged to do what I needed. Instead of changing fieldAverageTemplates.C with an additional variable (like, let's say, primeField), I tried to evaluate < u' c' >, < v' c' >, and < w' c' > in the following way:
mean value of U and c thanks the fieldAverage FO --> definition of the new variable U' (3 components vector) * c' as (U - UMean)*(c - cMean) --> mean value of this new variable.
I hope this is a valid approach since the fieldAverage code computes the iterative average.

pedroxramos January 30, 2020 05:35

Quote:

Originally Posted by elden (Post 744258)
Well,
I think I've menaged to do what I needed. Instead of changing fieldAverageTemplates.C with an additional variable (like, let's say, primeField), I tried to evaluate < u' c' >, < v' c' >, and < w' c' > in the following way:
mean value of U and c thanks the fieldAverage FO --> definition of the new variable U' (3 components vector) * c' as (U - UMean)*(c - cMean) --> mean value of this new variable.
I hope this is a valid approach since the fieldAverage code computes the iterative average.


hi,


would you mind sharing your script for this part?

elden January 31, 2020 07:40

1 Attachment(s)
Quote:

Originally Posted by pedroxramos (Post 756092)
hi,


would you mind sharing your script for this part?


This is the code. The C2H4 scalarField is the one being transported within the flow field

pedroxramos January 31, 2020 07:46

thanks a lot!


All times are GMT -4. The time now is 19:43.