Outline

1. Andreas KrumbeinGerman Aerospace CenterInstitute of Aerodynamics and Flow Technology, Numerical MethodsNormann KrimmelbeinTechnical University of BraunschweigInstitute of Fluid Mechanics, Aerodynamics of Aircraft 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 prediction • Automatic, no intervention of the user • Reduction of modeling 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 • Development of TAU transition prediction module by Institute of Fluid Mechanics, Technical University of Braunschweig in German research initiative MEGADESIGN

4. 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

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 + fully automated stability code + eN method • RANS solver + boundary layer code + eN database method(s) • RANS solver + transition closure model or transition/turbulence model

7. Coupling Structure cycle = kcyc cycle = kcyc Transition Prediction Coupling Structure

8. Coupling Structure • Transition Prediction Module: • 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

9. Coupling Structure • Hybrid RANS solver TAU: • 3D RANS, compressible, steady/unsteady • Unstructured/hybrid grids: hexahedra, tetrahedra, pyramids, prisms • Finite volume formulation • Vertex-centered spatial scheme (edge-based dual-cell approach) • 2nd order central schemes, scalar or matrix artifical dissipation • Time integration: explicit Runge-Kutta with multi-grid acceleration or implicit approximate factorization scheme (LU-SGS) • Turbulence models and approaches: • Linear and non-linear 1- and 2-equation eddy viscosity models (SA type, k-w type) • RSM  RST, EARSMs (full & linearized) • DES

10. 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)

11. 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

12. 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 9 (F1 WT) • 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

13. 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

14. 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

15. Results Skin friction grid 2 slat very small bubble transition locations: error reduced by 40% flap large bubble

16. Results Transition locations and separation grid 2 grid 2

17. 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 predcition 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