far-field drag breakdown applied to the dlr-f6 configuration · 2003. 8. 27. · 4turbulence model...

2nd CFD Drag Prediction Workshop

21st of June 2003

Far-field drag breakdownapplied to the DLR-F6 configurationIn the framework of the 2nd CFD Drag Prediction Workshop

2nd CFD DPW

Presented by

Stéphane AmantAerodynamic methods engineer

21st of June 20032nd CFD Drag Prediction Workshop Page 2

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Context of the topic

• To tackle the issue of aircraft performance4 Optimal shape design fi

need for reliable drag breakdown4 Cruise performance assessment fi

need for accurate overall drag level

• Prevailing role of CFD4 Generation of well adapted grids

4 Need for a breakthrough in drag assessment– information provided by near-field integration insufficient

– far-field abilities very attractive in terms of• improvement of the accuracy• physical drag breakdown• spatial distribution of drag sources


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Tools used by Airbus for the 2nd DPW

• Structured multiblock solver : elsA4Developed by ONERA4Oriented-object structure (C++)4Turbulence model : k-w (Wilcox)4 Centred scheme4Dissipation : Jameson type scalar scheme4Implicit time integration : LU-SSOR method

• Far-field drag analysis tool : FFD414developed by ONERA / Airbus France

(van der Vooren / Destarac‘s theory)4industrialized by Airbus France4daily used by shape designers and aerodynamic data

engineers4capability for dealing with patched grids (soon AMR grids)


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Comparison elsA / TAU of the drag polars(WB & WBPN configurations)

0,10

0,20

0,30

0,40

0,50

0,60

180,0 230,0 280,0 330,0 380,0 430,0

Cd (*10000.)

Cl Cd_total_WB (wind tunnel)

Cd_total_WB (elsA - ICEM grid)

Cd_total_WB (elsA - Airbus grid)

Cd_total_WB (TAU - medium)

Cd_total_WB (TAU - fine)

Cd_total_WBPN (wind tunnel)

Cd_total_WBPN (elsA - ICEM grid)

Cd_total_WBPN (TAU - medium)

Cd_total_WBPN (TAU - fine)

Cd_total_WBPN (elsA; -1,0°; fully turb.)

Drag polar (near-field integration)

10 drag counts

with forced transition

fully turbulent


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Cp distributions(elsA, medium ICEM grid, WBPN, CL=0.50)

with fixed transitionfully turbulent

Wing

Nacelle


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Physical and numerical drag breakdown

( ) iwvAfp DDDDD ++=+

( ) spD

spi

appiwvAfp DDDDDDD

i

++++=+43421

VWVV

• Exact near-field/far-field balance4no small disturbances assumption

• Numerical considerations4production of spurious drag

(connected to entropy variations in the flowfield)

4decay of axial vorticity in the wing-tip vortexfi transformation of induced drag into spurious drag


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Far-field analysis

• Comments4lower overall far-field drag fi removal of the spurious drag

4quite high discrepancy on the viscous terms fi

turbulence model ? role of the grid size ?

4 good agreement on the wave drag magnitude

4uncertainty on the induced drag : correction of the vortex decay ?

4incremental drag better predicted than the near-field for elsA– TAU : DCD = 41,2.10-4

– elsA : DCD = 45,9.10-4

SolverGridCDfCDvpCDwCDiCDtotalTAU8 750 330 nodes125.363.31.389.6279.5WBelsA5 715 968 cells(ICEM)135.056.00.991.2283.5TAU12 321 068nodes149.177.24.889.6320.7WBPNelsA8 290 304 cells(ICEM)159.173.24.692.5329.4


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Wave drag distribution

Excellent agreementon the local drag rise !

Valuable plotfor design improvement !


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Viscous drag distribution

The magnitude of the root separationin terms of drag is identically predicted !

Excellent agreement on the local drag rise !


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Drag breakdown from elsA computations(WB & WBPN configurations)

0,30

0,35

0,40

0,45

0,50

0,55

0,60

0,0 20,0 40,0 60,0 80,0 100,0 120,0 140,0 160,0 180,0

Cd (*10000.)

Cl

Cd_wave (WB)

Cd_wave (WBPN)

Cd_friction (WB)

Cd_friction (WBPN)

Cd_viscous_pressure (WB)

Cd_viscous_pressure (WBPN)

Cd_induced (WB)

Cd_induced (WBPN)

Drag polar breakdown (elsA computations)

Issue withthe enforced transition ?

Contribution of the lower side(interaction wing / pylon / nacelle)

Low impact of the engine installationon the induced drag


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[email protected]° : an example of analysis

Wing root separation

Wing/Pylon separation

AoA = -1.0° AoA = 0.0°

Physical intuition confirmed

by the far-field analysis

fi very valuable information

provided by FFD41


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Conclusions

• Far-field drag analysis tools = an intelligent means of makingthe most of CFD4shape design improvement (including optimisation)

4identification of CFD issues (grids, solvers, etc.)

4New sensors for automatic refinement

• Physical drag breakdown is available for both Airbus solvers(elsA & TAU)4discrepancies remain to be addressed

4some obvious satisfactory trends

• The one-drag count accuracy : a utopia4solver able to capture the flow features

4well-built grid

4far-field drag assessment tool

the 1 d.c. variationis at hand

far-field drag breakdown applied to the dlr-f6 configuration · 2003. 8. 27. · 4turbulence model...

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