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-   -   Some RANS Post-Processing basics (http://www.cfd-online.com/Forums/openfoam-post-processing/95433-some-rans-post-processing-basics.html)

chegdan December 17, 2011 10:04

Some RANS Post-Processing basics
 
Hello All,

I have nearly completed the arduous task of modeling some complex turbulent flow using a low RE k-epsilon RANS model (single-phase). The results look realistic, giving values close to experimental results, but I would like to look more at the flow field. I'm having issues with figuring out exactly what to compare and look at for a turbulent flow field. I know that different fields CFD (combustion, aero foils, multiphase modeling, etc.) care about different things have different objectives when performing CFD. However, something so new (the complex geometry that is being modeled) is at the stage of understanding the flow itself without optimizing a design parameter (yet)...what does one look at and describe it in a meaningful way?

Some of what I already know and have done or are going to do:

- uprime (existing utility)
- Cd: calculate drag coefficient using some of the tools floating around on the forum. (not sure which one to use yet)
- vorticty (existing utility)
- Helicity (custom utility)
- yPlus (existing utility)
- Overall pressure drop across the domain (using values from simpleFunctionObjects)
- wallShear (existing utility?)
- Turbulent Reynolds = nu_t/nu (perform in paraview or custom utility)
- Q and enstrophy?-> still figuring out how these two can help interrogate the flow.

What are people's thoughts on specific post-processing tasks and what are your suggestions to add to this list? Right now, I'm only interested in RANS, but I will also be doing some passive scalar transport in the turbulent flow, investigating the sensitivity to scalar-flux models. So, any suggestions for scalar post processing (steady and time-dependent) is also helpful.

I was hoping that this thread can inspire people to contribute an idea (or links on the forum) about a specific post-processing method (either from the suggested or in addition to) rather than asking programming specific to a post-processing tool or seeking a fix for something listed here.

Cheers.

florian_krause December 20, 2011 07:19

Hi Dan,
your list is already quite complete I would say and indeed there is the wallShearStress utility as well as the wallGradU utility in /OpenFOAM/OpenFOAM-2.0.1/applications/utilities/postProcessing/wall (not sure but I guess they exist in previous versions as well)

What kind of passive scalar transport are you calculating? In my cases, the passive scalar is a particle concentration and for validation purposes I'm calculating the friction concentration C_tau as defined in the reference below. Using that, I investigate the near-wall concentration profile C/C_tau over yPlus

I. Calmet and J. Magnaudet: Large-eddy simulation of high-Schmidt number mass transfer in a turbulent channel flow, Physics of Fluids, 9 (1997), 438455.

Best,
Florian


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