Integrated Experimental and Numerical Research on the .... Bergmann. A. Hübner. Integrated Experimental and Numerical Research on the Aerodynamics of Unsteady Moving Aircraft. 3rd

A. Bergmann

A. Hübner

Integrated Experimental and Numerical Research on the Aerodynamics of Unsteady Moving Aircraft

3rd International Symposium on Integrating CFD and Experiments in Aerodynamics

•Motivation•Test Setup•Numerical Approach•Typical Results•Outlook

21 June 2007Bergmann / Hübner

3rd International Symposium on Integrating CFD and Experiments in AerodynamicsUSAF-Academy

2

Motivation

Dynamic Derivatives are required for• Prediction of flight dynamics (candidate conf., design FCS, knowledge S&C)• Loads prediction for structural design of aircraft components • Data-Set for CFD validation process

Common method (for transport aircraft)• Assessment from simple handbook methods• Application of corrections (from flight tests)

Evaluation of flight characteristics is still an issue!

Evaluate and describe the aerodynamics in the manoeuvring flight regime



3

Dynamic Stability Testing of A/C NEEDS vs. CAPABILITIES

Low α (Transport aircraft)

High α (Space Shuttle, Concorde,

Fighter aircraft)

Flow mainly linear, often well known

strong non-linear effects (separation, transition, vortex shedding, etc.)

Analytical prediction of dynamic derivatives

easy (linear potential methods and various approximations often acceptable)

very difficult (highly non-linear, often speculative, approximations risky)

Magnitude of dynamic derivatives small sometimes very large, varying sign

Variation of dynamic derivatives with α

small sometimes very rapid

Effect of dynamic derivatives on flight trajectory and on stability and control

insignificant or at least constant and well-known

sometimes very large, may often be significant.

Situation in the 70ties (Orlik – Rückemann)

Changing interest in dynamic derivatives – high α

vs. low α



4

Today´s Situation

A380• relative short lever arm of tail unit• larger taper ratio• non-circular cross section

A400M• tail ramp• sponsons• T-tail

BWB• hybrid shape• short lever arms, small damping



5

Possible Future Situation

For new configurations semi empirical methods are not accurate as requiredHigh fidelity toolsImproved data accuracy

cnr

6 VSAERO, inviscidVSAERO, viscid 2 iter. ,Re = 2,1*10DNW-NWBHandbook Method

0 2 4 6α[o]

0 2 4 6α[o]

full configuration tail effect0 0



6

RotaryRotary--BalanceBalance of DNWof DNW--NWBNWB



7

MMobile OOscillatory DDerivative Balance (MOD) since 1970

Serial kinematic structure:Number of DoF is achieved by serial arrangement of the corresponding number of linear and rotative axes

The bottom-most axis of movement has to carry the weight of all those lying above it.

NOT well suited for the requirements> high stiffness> low mass

The errors (thermal, geometric, caused by loads) of movement of all axes are added

Oscillatory Motion Apparatus of DNW-NWB



8

OOscillatory MMotion SSystem (OMS) since 2000

Parallel kinematic structurebased on Stewart Platform

6 telescope like, driven legs 6DoF

Masses to be moved are smaller

Errors not added

Only forces in axial direction of the legs (largest stiffness)

Hydraulically driven

Available working space smaller compared to machine - size

Advancing the state of the art (1)



9

Use of the Hexapod System OMS…

…in combination with a gear box in the fuselage as coupled kinematics




10

Approach since 2003:

Investigation of an existing prototype of milling machine based on parallel kinematics

goal: develop an optimized system to meet the requirements of W/T model support

Principle of Rod kinematic6 rods with constant lengthrail guides, electically driven

Design and build a W/T dynamic test rig to investigate manoeuvring characteristics of future aircraft

6DOFrepresentative rates / ampl.




11

Advancing the state of the art (4), Requirements

6 DoF

Workspace (long., lateral, heave): 1100mm, 300mm, 500mm

Pivoting angles of - 5° to + 5° for rolling, accuracy < 0.005° -15° to + 7° for pitching < 0.01° -10° to +10° for yawing < 0.005°

Near constant and high stiffness all over the workspace

First eigenfrequency > 20 Hz

Max acceleration 2.5 g

Oscillatory Motion of the model in the modesYawing, Pitching, Rolling, (Heave) up to 3 Hz with 5°(60mm) Amplitude

Max payloads Fx / Fy / Fz 1500 / 1000 / 5000 N Mx / My / Mz 500 / 1000 / 600 Nm



12

Cutting-Edge Support MModel PPositioning MMechanism (MPM) of NWB

•Use of conventional standard components cheaper•Use of six constant length rods made from CRP small masses, high stiffness (1400N/µm)•Reduction to two parallel tracks unique design of a parallel kinematic, cheaper, simpler•Use of linear electromagnetic motors highest accuracy and highest dynamic



13

MModel PPositioning MMechanism (MPM)

Max Force: 20,700 NVelocity at Fmax up to 6 m/sec



14

The unique MPM for dynamic testing in the open testsection of NWB



15

f [Hz]

Ampl

itude

0 5 10 15 20 25 30 35

10-4

10-3

10-2

10-1OMSMPM

t [s]

Mz

[Nm

]

1 1.2 1.4 1.6 1.8 2-80

-60

-40

-20

0

20

40

60

80

OMSMPM

t [s]

Ψ[°]

1 1.2 1.4 1.6 1.8 2-6

-4

-2

0

2

4

6

OMSMPM

f [Hz]

Am

plitu

de

0 5 10 15 20 25 30 3510-3

10-2

10-1

100OMSMPM

Comparison OMS vs. MPM Yawing Motion, f=2.1Hz

Position Yawing Moment



16

t [s]

My

[Nm

]

1 1.2 1.4 1.6 1.8 2-150

-100

-50

0

50

100

150OMSMPM

f [Hz]

Am

plitu

de

0 5 10 15 20 25 30 35

10-4

10-3

10-2

10-1OMSMPM

f [Hz]

Am

plitu

de

0 5 10 15 20 25 30 35

10-3

10-2

10-1

100OMSMPM

t [s]

Φ[°

]

1 1.2 1.4 1.6 1.8 2-6

-4

-2

0

2

4

6OMSMPM

Comparison OMS vs. MPM Pitching Motion, f=2.8Hz

Position

Pitching Moment



17

unsteady heave osc.Cmα

..unsteady pitching motion

Cmα

+ Cmq

quasi-steady motionCmq

= +

Dynamic Derivatives

Roll Clp Cnp CYp = f (p)

Pitch (CDα

+CDq ) CLα

+CLq Cmα

+Cmq = f (α,q)

Yaw Clr - Clβ

Cnr - Cnβ

CYr - CYβ

= f (β,r)

Heave ocs. CWα

CAα

Cmα

= f (α)

Lateral osc. Clβ

Cnβ

CYβ

= f (β)

.

. . .

. . .

. . .

. .

.

.

.

.



18

Cmq+ CmαCLq+ CLα..

α [°]-1 0 1 2 3 4 5 6 7 8

0

1

2

3

4

5

6

7

8

9

10

11

12

OMS, optical systemMPM, optical system

α [°]-1 0 1 2 3 4 5 6 7 8

-30

-25

-20

-15

-10

-5

0

5

OMS, optical systemMPM, optical system

Experimental results from OMS and MPM of the DLR-F12 geometry



19

Cmq+ CmαCLq+ CLα..

α [°]-1 0 1 2 3 4 5 6 7 8

0

1

2

3

4

5

6

7

8

9

10

11

12

MPM, electrical sensorMPM, optical system

α [°]-1 0 1 2 3 4 5 6 7 8

-30

-25

-20

-15

-10

-5

0

5

MPM, electrical sensorMPM, optical system

Impact of diff. position measurement techniques on the derivatives of the pitching motion



20

The panel method: VSAERO

• subsonic panel method for arbitrary body geometry• wake shape relaxation• skin friction and boundary layer displacement• quasi-steady rotations

Panel model of the DLR-F12 model constant roll motion

constant pitch motion

constant yaw motion



21

Hybrid Navier-Stokes Solver DLR TAU-code

• solution of RANS equations for arbitrary moving bodies on unstructured meshes

• independent of grid cell type (hybrid meshes)• various turbulence models• grid adaptation (refinement & de-refinement)• designed for massively parallel computers• validated for increasing number of test cases• routinely used by DLR and Aircraft Industry• quasi steady / unsteady movements

(steady/unsteady flow)



22

Different shares of derivatives for Euler results, DLR-F12 geometry (1)

α0 [°]-1 0 1 2 3 4 5 6 7-30

-25

-20

-15

-10

-5

0.Cmq + Cmα

α0 [°]-1 0 1 2 3 4 5 6 7-2

0

2

4

6

8

10

12

VSAERO, invis.Euler, quasi-steadyEuler, unsteady

.CLq + CLα



23

α0 [°]-1 0 1 2 3 4 5 6 7-2

0

2

4

6

8

10

12

Euler, quasi-steadyEuler, unsteadyEuler, unsteady, heave osc.

.CLq + CLα

α0 [°]-1 0 1 2 3 4 5 6 7-30

-25

-20

-15

-10

-5

0.Cmq + Cmα




24

α0 [°]-1 0 1 2 3 4 5 6 7-2

0

2

4

6

8

10

12

Euler, quasi-steadyEuler, unsteadyEuler, unsteady, heave osc.Euler, quasi + heave osc.

.CLq + CLα

α0 [°]-1 0 1 2 3 4 5 6 7-30

-25

-20

-15

-10

-5

0.Cmq + Cmα




25

Comparison of numerical and experimental results, DLR-F12 geometry

α0 [°]-1 0 1 2 3 4 5 6 7-2

0

2

4

6

8

10

12

DNW-NWB, A/CEuler, unsteadyNa-St., unsteady

.CLq + CLα

α0 [°]-1 0 1 2 3 4 5 6 7-30

-25

-20

-15

-10

-5

0.Cmq + Cmα



26

t [s]

Δα[°

]

F N[N

]/Am

pl(E

xp)[

N]

My

[Nm

]/Am

pl(E

xp)[

Nm

]

0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65-5

-4

-3

-2

-1

0

1

2

3

4

5

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

FN, Exp.My, Exp.Δα, Exp.FN, EulerMy, EulerΔα, EulerFN, Na-St.My, Na-St.Δα, Na-St.

Δt

DLR-F12, pitching motion, comparison of experimental and numerical results



27

phase of FL [°]

CLq

+C

Lα

-178 -177 -176 -175 -174 -173 -172 -171 -170 -1690

4

8

12

16

CLq + CLα

Y = A + B*XA = 2.62 E+2B = 1.46 E+0

R2 = 0.999996

. .

..

determined phase(from calc. and exper.)

Effects of phase error: Derivative of the pitching oscillation



28

phase of FL [°]

phase of My [°]

CLq

+C

Lα

Cm

q+

Cm

α

-178 -177 -176 -175 -174 -173 -172 -171 -170 -169

-91 -90 -89 -88 -87 -86 -85 -84 -83 -82

0

4

8

12

16

-28

-26

-24

-22

-20

CLq + CLα

Cmq + Cmα

Y = A + B*XA = 2.62 E+2B = 1.46 E+0

R2 = 0.999996

Y = A + B*XA = -7.37 E+1B = -5.79 E-1

R2 = 0.999822

. .

..

determined phase(from calc. and exper.)

Effects of phase error: Derivative of the pitching oscillation



29

α [°]-1 0 1 2 3 4 5 6 7

-23.0

-22.0

-21.0

-20.0

-19.0

-18.0

-17.0

-16.0

-15.0

-14.0

-13.0

wing without bendingwing with bending

Cmq

α [°]-1 0 1 2 3 4 5 6 7

6.0

6.2

6.4

6.6

6.8

7.0

7.2

7.4

7.6

7.8

8.0

wing without bendingwing with bending

CLq

Outlook (1)

Assumption so far: ideal rigid model without deformation

Very first results from VSAERO for a rigid bended wing (quasi steady)



30

• Investigation of a new elastic wind tunnel model in 2007• Determination of the unsteady wing shape during the motion• Measurements of the unsteady pressure distribution • Numerical investigations with multidisciplinary codes with coupled

aerodynamic-structural solvers

Outlook (2)

Documents

Integrated Experimental and Numerical Research on the .... Bergmann. A. Hübner. Integrated Experimental and Numerical Research on the Aerodynamics of Unsteady Moving Aircraft. 3rd