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Automatic Transition Prediction and Application to 3D High-Lift Configurations

Automatic Transition Prediction and Application to 3D High-Lift Configurations. Andreas Krumbein German Aerospace Center - DLR Institute of Aerodynamics and Flow Technology, Numerical Methods. Outline. Outline. Introduction Transition Prediction Coupling Structure Test Cases

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Automatic Transition Prediction and Application to 3D High-Lift Configurations

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  1. Automatic Transition Prediction and Application to 3D High-Lift Configurations Andreas KrumbeinGerman Aerospace Center - DLRInstitute of Aerodynamics and Flow Technology, Numerical Methods

  2. Outline Outline • Introduction • Transition Prediction Coupling Structure • Test Cases • Computational Results • Conclusion • Outlook

  3. Introduction Introduction • Aircraft industry 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

  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 • Objectives of the talk: • Documentation of the 1st application of the complete system to an industrially relevant aircraft configuration with a multi-element wing • Documentation of the results for different flow conditions: fully turbulent flow, flow with prescribed and predicted transition • Demonstration that the technique is ready to be applied to complex configurations • Demonstration that the underlying procedure yields reasonable results for a complex configuration

  7. Coupling Structure cycle = kcyc Transition Prediction Coupling Structure

  8. Coupling Structure • Transition Prediction Module: • Laminar boundary-layer method for swept, tapered wings (conical flow) • eN database-methods for Tollmien-Schichting and Cross Flow instabilities • Laminar separation approximates transition if transition downstream of laminar separation point • 2d, 2.5d (infinite swept) + 3d wings • Single + multi-element configurations • N factor integration along chordwise gridlines • Attachment line transition, by-pass transition & transition inside laminar separation bubbles not yet covered

  9. Coupling Structure • Structured RANS solver FLOWer: • 3D RANS, compressible, steady/unsteady • Structured body-fitted multi-block meshes • Finite volume formulation • Cell-vertex and cell-centered spatial discretizations schemes • Central differencing, 2nd & 4th order artificial dissipation scaled by largest eigenvalue • Explicit Runge-Kutta time integration • Steady: local time stepping & implicit residual smoothing, embedded in a multi-grid algorithm • eddy viscosity TMs (Boussinesq) & alg./diff. RSMs

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

  11. Test Cases Test Cases • KH3Y geometry (DLR F11 model) • Half-model with Airbus A340 fuselage • Wing-body with full span slat and flap high-lift system • Landing configuration: dS = 26.5°, dF = 32.0° • Measurements • European High Lift Programme (EUROLIFT), partly funded by EU • Airbus LSWT (Bremen, Germany) • Re = 1.35 mio., M = 0.174 • Transition band on fuselage, 30mm downstream of the nose

  12. Test Cases • Computations • a = 10.0° and 14.0° • Fully turbulent, prescribed & predicted transition • Spalart-Allmaras one-equation TM with Edwards & Chandra mod. • 97 blocks, 5.5 mio. points, 96.500 on surface • Transition prediction in sections: 11 on slat 13 on main wing 13 on flap • Calibration of critical N factors: a = 10°, hot film on main wing upper side at 68% span  (xT/c)main = 0.08  NTS = 4.9 No indications for CF  NCF = NTS

  13. Test Cases • ‘Point transition‘ (no transitional flow model) • Prescribed transition lines: hot film data slat &main wing 68% span a = 10°, upper side a = 10°, lower side

  14. Results Computational Results • a = 10.0°, upper side: laminar surface regions a = 10°, upper side prescribed a = 10°, upper side predicted

  15. Results • a = 10.0°, lower side: laminar surface regions a = 10°, lower side prescribed a = 10°, lower side predicted

  16. Results • a = 14.0°, upper side: laminar surface regions a = 14°, upper side prescribed a = 14°, upper side predicted

  17. Results TS TS TS TS CF TS CF CF CF • a = 14.0°: laminar surface regions & transition labels a = 14°, upper side predicted a = 14°, lower side predicted

  18. Results • Comparison ofprescribed & predicted transition lines a = 10°, upper side predicted a = 14°, upper side predicted calibration point for NTS section of the hot films

  19. Results • Comparison ofcp-distributions: h = 0.20, 0.38, 0.66, 0.88 a = 14.0°

  20. Conclusion Conclusion • The complete coupled system (RANS solver & transition prediction module) was succesfully applied to a complex aircraft configuration of industrial relevance  WB with 3-element high-lift system • The predicted transition lines are reasonable and quite different from estimated ones based on an experiment • But, they are of preliminary character: • Transition prediction module does not yet cover all transition mechanisms which can occur in 3d high-lift flows • Transition inside laminar separation bubbles, attachment line transition & by-pass trasition can not be detected • More validation on complex configurations necessary • It seems to be evident that transition inside laminar separation bubbles is of high importance • It was shown that a fully turbulent simulation or an estimation of the transition lines can result in significant deficiencies

  21. Outlook Outlook • Further comparisons for the current tast cases: • Skin friction lines vs. flow visualizations • Global coeffcients: lift & drag • More validation cases, e.g. DLR F5 wing → transonic test case & other more complex test cases • Empirical criteria for:- transition inside laminar separation bubbles - attachment line transition - bypass transition • Incorporation of a fully automated linear stability code into the transition prediction module → alternative for database methods • Consideration of relaminarization Acknowledgments: • Work carried out in EUROLIFT II project, partly funded by EU • Computational grid provided by Airbus Germany

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