High-Lift Airfoil Computations with Automatic Transition Prediction using the DLR TAU Code

1. Andreas KrumbeinGerman Aerospace CenterInstitute of Aerodynamics and Flow Technology, Numerical Methods Navier-Stokes High-Lift Airfoil Computations with Automatic Transition Prediction using the DLR TAU Code

2. Outline Outline • Introduction • Transition Prediction Coupling Structure • Test Case: 2D A310 take-off configuration • Computational Results • Conclusion • Outlook

3. Introduction Introduction • Aircraft industry and research requirements: • RANS based CFD tool with transition handling • Better numerical simulation results • Capturing of otherwise unconsidered physical phenomena • At first: impact on lift and drag • Characteristics • Transition prescription • Transition prediction • Modelling of transitional flow areas • Automatic: no intervention of the user • Autonomous: necessary user information as little as possible

4. Introduction Introduction • Reduction of modelling based uncertainties • Accuracy of results from fully turbulent flow or flow with prescribed transition often not satisfactory • Improved simulation of the interaction between transition locations and separation • At first in FLOWer code • 3d multi-element wing configurations • Later in TAU code • 3d multi-element wing configurations • Fuselages and nacelles • TAU transition prediction module developed by Institute of Fluid Mechanics, Technical University of Braunschweig in German research initiative MEGADESIGN

5. Introduction • Different approaches: • RANS solver + stability code + eN method • RANS solver + boundary layer code + stability code + eN method • RANS solver + boundary layer code + eN database method(s) • RANS solver + transition closure model or transition/turbulence model

6. Introduction • Different approaches: • RANS solver + stability code + eN method • RANS solver + boundary layer code + stability code + eN method • RANS solver + boundary layer code + eN database method(s) • RANS solver + transition closure model or transition/turbulence model

7. Introduction • Different approaches: • RANS solver + stability code + eN method • RANS solver + boundary layer code + stability code + eN method • RANS solver + boundary layer code + fully automated stability code + eN method • RANS solver + boundary layer code + eN database method(s) • RANS solver + transition closure model or transition/turbulence model

8. Coupling Structure cycle = kcyc Transition Prediction Coupling Structure FLOWer

9. Coupling Structure cycle = kcyc Transition Prediction Coupling Structure FLOWer & TAU

10. Coupling Structure cycle = kcyc cycle = kcyc Transition Prediction Coupling Structure FLOWer & TAU TAU

11. Coupling Structure • Transition Prediction Module of TAU: • RANS infrastructure part: BL data from RANS grid (BL mode 2)  Transition inside separation bubble possible  High mesh density necessary • External codes: • Laminar boundary-layer method COCO(G. Schrauf) for swept, tapered wings (BL mode 1)  Transition inside separation bubble NOT possible  Laminar separation approximates transition if transition downstream of laminar separation point • eN database-methods for TS and CF instabilities (PD mode 1) • Local, linear stability code LILO(G. Schrauf)(PD mode 2) • 2d, 2.5d (infinite swept) + 3d wings + 3d fuselages/nacelles (only BL mode 2) • Single + multi-element configurations • N factor integration along: • Line-in-Flight cuts • Inviscid streamlines • Attachment line transition & by-pass transition not yet covered

12. Coupling Structure • Transition Prescription: • Automatic partitioning into laminar and turbulent zones individually for each element • Laminar points: St,p  0 PTupp(sec = 2) PTupp(sec = 1) PTupp(sec = 3) PTupp(sec = 4)

13. Coupling Structure no yes STOP • Algorithm: set stru and strl far downstream compute flowfield check for RANS laminar separation  set separation points as new stru,l clconst. in cycles call transition module  use outcome of prediction method (PD modes 1&2) or BL laminar separation point (BL mode 1) set new stru,l underrelaxed  stru,l = stru,ld, 1.0 < d < 1.5 convergence check Dstru,l < e

14. FLOWer results upper side lower side • Transition lines for 11 wing sections h = 0.000, 0.110, 0.220, 0.325, 0.420, 0.800, 0.860, 0.900, 0.930, 0.960, 0.975 • Calibration of both critical N factors for lower side and a = 5°: NCFcr = 5.157 → h = 0.42 NTScr = 4.75→ h = 0.96 • ONERA M6 wing • a = 0°, 5°, 10°, 15° • Re = 3.5106 • M = 0.262 upper side lower side taken from *) TS ls a = 0° a = 0° ls a = 5° a = 5° a = 15° a = 15° TS TS all ls *)Schmitt, V., Cousteix, J., “Étude de la couche limite tridimensionelle sur une aile en flèche,” ONERA Rapport Technique N° 14/1713 AN, Châtillon, France, July 1975 CF all ls all CF

15. FLOWer results • TC 214 from EUROLIFT II • Re = 1.35 mio., M = 0.174, SAE, eN database methods a = 14°, upper side predicted a = 14°, lower side predicted

16. FLOWer results TS TS TS TS CF TS CF CF CF • TC 214 from EUROLIFT II • Re = 1.35 mio., M = 0.174, SAE, eN database methods a = 14°, upper side predicted a = 14°, lower side predicted

17. FLOWer results • Comparison ofcp-distributions: h = 0.20, 0.38, 0.66, 0.88 a = 14.0°

18. Test Case • 2d A310 take-off configuration • M = 0.221, Re = 6.11 x 106, a = 21.4° • grid 1: 22,000 points grid 2: 122,000 points, noses refined • SAE turbulence model • prediction on upper sides, lower sides fully laminar, NTS 8.85 (F1) • exp. Transition locations  slat: 15% & flap: 34.5% kink on main upper side  19% • different mode combinations: a) BL mode 1 & PD mode 1  BL code & TS database method b) BL mode 1 & PD mode 2  BL code & stability code c) BL mode 2 & PD mode 2  BL in TAU & stability code Test Case

19. TAU results Surface pressure grid 1 grid 2 a.) & b.) results identical  all lam. seps. a.) & b.) results identical  all lam. seps. c.) no convergence  grid too coarse c.) all from stability code

20. TAU results Skin friction grid 1 grid 2 a.) & b.) no separation bubbles a.) & b.) very small sep. bubble on slat c.) no convergence c.) much larger slat bubble & flap improved

21. TAU results Skin friction grid 2 slat very small bubble transition locations: error reduced by 40% flap large bubble

22. TAU results Transition locations and separation grid 2 grid 2

23. TAU results Transition locations and separation grid 2 grid 2

24. Conclusion/Outlook • TAU transition prediction module works fast and reliable for 2d multi-element configurations • Transition inside laminar separation bubbles can be detected with high accuracy when appropriate prediction approach is used • Therefor, high grid densities are required • much more testing necessary: • more test cases needed with TS transition (e.g. CAST 10, A310 landing) • full aircraft WB+HTP+VTP (wing with full-span flap without slit) • WB high-lift configuration with full-span slat and flap from EUROLIFT II • transition criteria: - transition in lam. sep. bubbles - attachment line transition - by-pass transition • development of a stream-line oriented bl code with transverse pressure gradientCOCO-3d → replaces COCO in 2007 • unsteady transition prediction method based on eN method • alternative approaches based on transport equations in future DLR T&T-project RETTINA done by TU-BS