'NASA_VERIF-2DZP' simulation project by pfernandez


#1

I created a new simulation project called 'NASA_VERIF-2DZP':

NASA's Turbulence Modelling Resource was created with the purpose of offering documentation on the various RANS turbulence models available and some reference cases to verify the implementation of such models.

Albeit the differences in the implementation of the models in OpenFOAM and NASA documentation, with this project we will see if we can get comparable results.


More of my public projects can be found here.


#2

@pfernandez, another great project you’ve got going here! Keep me updated on the results and we can definitely look into adding your findings into our verification and validation documentation.


#5

@pfernandez - this is great! Looking very much forward to seeing the final results.


#6

As already mentioned, the NASA Turbulence Modelling Resources (TMR) offer a way to verify and validate the implementation of RANS turbulence models. There is a difference between one and the other:

  • verificacion refers to the implementation of the models. Verification cases are used to check correct implementation of turbulence models across different solvers by comparing results under similar simulation settings.
  • validation refers to the solutions. Validation uses experimental data to compare with CFD results within a range of predefined physical conditions.

For this case, the meshes and results avaible at TMR are intended for verification. As Gomez (2014) notes in his Thesis, OpenFOAM’s implementation of the k-omega SST turbulence model needs for some adjustments in order to make it equal to NASA’s implementation. As it is not possible to modify any of the code in SimScale (for safety reasons), we will just show how some of the results change as mesh resolution increases.

Update: I realized I was using the k-omega turbulence model (Wilcox, 1988), so I updated the comparison charts accordingly; although NASA provides verification data only for the Wilcox (2006) implementation.

In order to get some additional results to post-process we make use of function objects and standard utilities. For instance,

foamCalc mag U

generates a new file magU within each time-step containing the absolute value of the velocity at each cell and at the boundaries. We can then sample for pressure, velocity, and viscosity along a line at x=0.97 with this sampleDict.

Following figure shows the mean velocity profile at different mesh resolutions.

All resolutions get us approximately the same profile; although there are significant differences when we compare our results against those from NASA (remember that NASA uses a different implementation of the k-omega turbulence model).

On the other hand, the dimensionless eddy viscosity profile shows a strong dependency on the mesh resolution.

If we compare this results with NASA’s, the difference is somewhat bigger.

References

Gomez, Sebastian. 2014. “Verification of Statistical Turbulence Models in Aerodynamic Flows.” MSc Thesis, Albuquerque: University of New Mexico. http://repository.unm.edu/handle/1928/24484.

Wilcox, David C. 1988. “Reassessment of the Scale-Determining Equation for Advanced Turbulence Models.” AIAA Journal 26 (11): 1299–1310. doi:10.2514/3.10041.

Wilcox, David C. 2006. Turbulence Modeling for CFD. 3rd ed. La CĂŁnada, Calif: DCW Industries.


#8

For some reason, I was using the k-omega turbulence model (Wilcox, 1988) instead of the k-omega SST turbulence model (Menter, 2003) which was my first intention, as that is the turbulence model used in Gomez (2014). Anyway, I updated the case and those are the new results.

As we can appreciate, despite the differences in the implementation of the models —NASA uses the Menter (1994) implementation—, results are now much closer to what is expected.

References

Menter, F. R. 1994. “Two-Equation Eddy-Viscosity Turbulence Models for Engineering Applications.” AIAA Journal 32 (8): 1598–1605. doi:10.2514/3.12149.

Menter, F. R., M. Kuntz, and R. Langtry. 2003. “Ten Years of Industrial Experience with the SST Turbulence Model.” In Turbulence, Heat and Mass Transfer 4, edited by K. Hanjalić, Y. Nagano, and M. Tummers, 625–32. Antalya, Turkey: Begell House, Inc.