1. Transition locations on the LEISA high lift airfoil S.Reuß

2. Available experimental data
Two different settings were measured:
3eOptV1 which was measured in the slotted test section of the low speed wind tunnel NWB. From this measurement infra red pictures as well as pressure distributions are available.
3eOptV2 which was measured in the closed test section of the NWB. From this measurement pressure distributions as well as accoustical measurements are available.
All grids are for the OptV2 geometry, but the difference between those two is minimal:

3. Available experimental data
First we got the infrared measurement for the 3eOptV1 and the pressure distribution of the 3eOptV2 both for α=7° angle of attack. A comparison of the pressure distributions for the two different test sections (slotted/closed) revealed strong deviations (see next 3 slides)
After consultation with the experimentalists it was clear, that we needed a different angle of attack for comparison with the data from the slotted test section. The suggestion was to use the α=8° case. Also the suspicion arouse, that there might occur transition on the slat for this angle of attack.
Now that we received the infrared pictures for the other incidence angles, it is clear, that no transition should be found on the slat.
Since no evaluated data is available, we conclude by simple optical judgment, that the transition locations for the α= 7° and α=8° case do not change significantly

4. Available experimental data Pressure distribution slat
OptV2 (closed section)
OptV1 (slotted section)
Data is measured in three
sections

5. Available experimental data Pressure distribution wing
Pressure distributions
OptV2 (closed section)
OptV1 (slotted section)
Data is measured in three
sections

6. Available experimental data Pressure distribution flap
Pressure distributions
OptV2 (closed section)
OptV1 (slotted section)
Data is measured in three
sections
Here the influence of the wind tunnel side walls can be clearly seen. The curves with the most points are the measurements at the mid section

7. Available experimental data IR slat and main wing upper side, α=7°
Flow

8. Available experimental data IR slat and main wing upper side, α=8°
Flow

9. Available experimental data IR slat and main wing upper side, α=9°
Flow

10. Available experimental data IR slat and main wing upper side, α=10°
Flow

11. Available experimental data IR slat and main wing upper side, α=11°
Flow

12. Available experimental data IR slat and main wing upper side, α=12°
Flow

13. Available experimental data IR wing and flap upper side, α=7°
Flow

14. Available experimental data IR wing and flap upper side, α=8°
Flow

15. Available experimental data IR wing and flap upper side, α=9°
Flow

16. Available experimental data IR wing and flap upper side, α=10°
Flow

17. Available experimental data IR wing and flap upper side, α=11°
Flow

18. Available experimental data IR wing and flap upper side, α=12°
Flow

19. New numerical results Spalart Allmaras Model
A new grid was built with some modifications:
The farfield distance was increased to 100c
The resolution of the three element noses was reduced a bit
The resolution of the slat wake and above the flap was increased
The resulting grid has again about points per layer
Calculations with this new grid showed a clear difference compared to those on the old grid (2d/3d hybrid grid that can be found on the ATAAC site)
These differences are due to the small farfield distance! Calculations with farfield vortical correction show a clear trend towards the new results
New calculations use a critical N-factor of 7.18, where the theoretically expected value is in the range of 7.18 to 7.3. Originally this value should be calibrated using the experimentally given transition locations, but since all calculations showed earlier transition, this procedure was not successful.

20. Pressure distribution comparison old/new grid SA model

21. Pressure distribution new grid SA model
With the new grid a corrected angle of attack of α=5° is needed when the Spalar-Allmaras model is used
Even though the pressure distribution does not show the plateau on the flap the flow seperates

22. Skin friction new grid SA model
With the new grid a corrected angle of attack of α=5° is needed when the Spalar-Allmaras model is used
Even though the pressure distribution does not show the plateau on the flap the flow seperates

23. Convergence new grid SA model
The RANS calculations with the SA model converge, but slower as with the old grid, where about iterations were sufficient

24. Pressure distribution new grid SST model
With the new grid a corrected angle of attack of α=6° is needed when the Menter-SST model is used

25. Skin friction new grid SST model
With the new grid a corrected angle of attack of α=6° is needed when the Menter-SST model is used

26. Convergence new grid SST model
The RANS calculations with the SST model do not converge in steady calculations

27. Convergence new grid SST model
An unsteady restart from the steady solution yields a converged solution (time step is scaled for better presentability)

28. Transition locations on new grid
The black lines indicate the old suggested transition locations. With the new grid and Ncrit=7.18 the SA model yields transition on the slat.
4° and 5° transition lines coincide

29. New recommendations
We recommend to use the new grid, to prevent wrong results because of the small farfield distance (Can be found on the ATAAC site as hybrid_mandatory)
We recommend to use the SA model with a corrected angle of attack of α=5° and following transition locations:
We recommend to use the SST model with a corrected angle of attack of α=6° and following transition locations:
Since the SST model shows a much better agreement with the experimental data, DLR is considering to use SST based DES.
*) The transition location on the lower side of the wing did not converge completely, but is considered to have small influence. No experimental data is available for the lower side.
Slat
Wing
Flap
Upper side
Laminar
xtr=0.189
xtr=0.953
Lower side
xtr= *
Upper side
Laminar
xtr=0.1815
xtr=0.949
Lower side
xtr= *

30. Wiggles in Pressure distribution
At several point some wiggles in the pressure distribution could be observed. A close look to the surfaces built by centaur reveals the reason: The surface normals at some cells deviate noticeably from the neighboring ones
I do not have an idea how to prevent centaur from producing such bad cells