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-   -   Post-stall behaviour of airfoils using different turbulence models (https://www.cfd-online.com/Forums/openfoam-verification-validation/227186-post-stall-behaviour-airfoils-using-different-turbulence-models.html)

ColourAshRed May 20, 2020 07:25

Post-stall behaviour of airfoils using different turbulence models
 
2 Attachment(s)
I am simulating a NACA0012 airfoil, from 0 to 180 degrees, and comparing the cl and cd results with NASA's experimental results. Up to stall, the Spalart-Allmaras model works just fine.

However, I am unable to get converging results using the k-epsilon model even at low angles of attack even after 20k iterations. I have set the y-plus value to 30, my Reynolds number is 700k. I will be attaching my 0/ and system/ files. Can someone please take a look and tell me where I've gone wrong or what I'm missing?

I have tried various things but I'm unable to set this right. I also want to know how to access the damping functions setting for the k-epsilon model in order to perform simulations for y-plus between 1&5.

If someone can also direct me on any resource on how to use the k-omega and k-omega SST models for separated flow over airfoils, it would be very generous and would help me a lot. I'm new to CFD on OpenFOAM, and this is my first project.

Thanks in advance!

mzzmrt May 28, 2020 06:34

At post-stall range, the thing is unsteady and you have to use transient solvers in this area.

At post-stall, modeling the turbulence is more tricky and since the real turbulence has full 3D structure, using a 2D model will be over simplification.

RANS/URANS models have serious limitations in this range so you have to switch better models such as DES etc. try to represent the physical phenomena more realistically but this will require much more computational power or time for the same problem.

ColourAshRed May 28, 2020 07:19

Quote:

Originally Posted by mzzmrt (Post 772330)
At post-stall range, the thing is unsteady and you have to use transient solvers in this area.

At post-stall, modeling the turbulence is more tricky and since the real turbulence has full 3D structure, using a 2D model will be over simplification.

RANS/URANS models have serious limitations in this range so you have to switch better models such as DES etc. try to represent the physical phenomena more realistically but this will require much more computational power or time for the same problem.

Thank you!
So, I take it that you would suggest a 3D model of the wing itself? What OpenFoam solvers would you suggest?

mzzmrt May 28, 2020 09:48

Not really. I mean using a mesh by extruding the profile in side direction with enough elements (say 32 or more depending on the conditions) to capture the flow features.

As an example see this page http://www.cttc.upc.edu/node/140

You can easily find papers dealing with this type of problem.


As a solver you will need pisoFoam or pimpleFoam.


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