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Andreas Krumbein German Aerospace Center Institute of Aerodynamics and Flow Technology, Numerical Methods Normann Krimmelbein Technical University of Braunschweig Institute of Fluid Mechanics, Aerodynamics of Aircraft.

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Presentation Transcript
slide1
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

slide2
Outline

Outline

  • Introduction
  • Transition Prediction Coupling Structure
  • Test Case: 2D A310 take-off configuration
  • Computational Results
  • Conclusion
  • Outlook
slide3
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
slide4
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
slide5
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
slide6
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
slide7
Coupling Structure

cycle = kcyc

cycle = kcyc

Transition Prediction Coupling Structure

slide8
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
slide9
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
slide10
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)

slide11
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

slide12
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

slide13
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

slide14
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

slide15
Results

Skin friction

grid 2

slat

very small bubble

transition locations:

error reduced by 40%

flap

large bubble

slide16
Results

Transition locations and separation

grid 2 grid 2

slide17
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

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