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59. Deutscher Luft- und Raumfahrtkongress Vortrag Nr. 1341
Experimental investigation of transonic fluid-structure interaction phenomena
at a high aspect ratio swept wing P. C. Steimle*
Aerodynamisches Institut, RWTH Aachen *HE Space Operations GmbH
Steimle - Experimental investigation of transonic fluid-structure interaction phenomena at a high aspect ratio swept wing 2
■ Dynamic shock - boundary layer interaction is major reason for aeroelastic instabilities in transonic flight
■ Accurate prediction of local and global interaction between the wing structure and transonic flow by numerical simulation necessary for future highly elastic wing designs
■ Transport type wings exhibit structural response to unsteady aerodynamic loads in their first bending – torsion mode
■ Acquisition and analysis of 3D time-resolved flow data to contribute to the understanding of aerodynamic unsteadiness in transonic flow
■ Simulation of wing flutter response to the unsteady aerodynamic field by harmonic oscillations in pure pitch and heave DOF
Introduction
Flutter stability limit in transonic flight regime
Steimle - Experimental investigation of transonic fluid-structure interaction phenomena at a high aspect ratio swept wing 3
Introduction
)sin(10 tαωαα +
)sin(1 tsh
hω
Harmonic pitch oscillation
Harmonic heave oscillation
■ Reduction of aero-structural interaction to focus on the aerodynamic problem
■ Harmonic oscillations of a swept wing model in pitch and heave to simulate wing flutter
Steimle - Experimental investigation of transonic fluid-structure interaction phenomena at a high aspect ratio swept wing 4
Experimental setup: Swept wing model
■ Highly stiff wing model to uncouple structural and flow response
■ Usage of UHM carbon fiber composite sandwich structure
■ Pressure sensors incorporated one wing section in the area of highest aerodynamic loading
■ Flow analysis tools □ Oil flow visualization
□ Time-resolved pressure distributions cp(t) from in-situ pressure sensors in one pressure tap section in y = 80mm
□ Pressure-sensitive luminescent paint on open anodic aluminum binder
□ Photogrammetric wing deformation measurement
M∞
optical markers
Supercritical wing section BAC 3-11/RES/30/21
Mean aerodynamic chord = 74.3 mm
Pressure tap section length c1 = 82.71 mm
LE sweep 34° TE sweep 22° and 26°
Aspect Ratio 10.3
c
Steimle - Experimental investigation of transonic fluid-structure interaction phenomena at a high aspect ratio swept wing 5
Trisonic wind tunnel of the RWTH Aachen University
Test section 0.4m x 0.4m Mach number 0.4 - 3.0 Testing time 2 - 5s Unit Reynolds number 1.5 x 107m-1
2-D adaptive test-section 0.80.84
0.880.92
0.96
0.40.5
0.60.7
0.8
0
2
4
6
8x 106
M∞ω*
|p′ |2 /f s [P
a2 /Hz]
Pressure fluctuations in empty test section
M∞ x2
z2
Experimental setup: Wind tunnel facility
Steimle - Experimental investigation of transonic fluid-structure interaction phenomena at a high aspect ratio swept wing 6
200 300 400 500 600 700 800Wavelength [nm]
Inte
nsity
[arb
itrar
y sc
ale]
ambient pressure vacuum
PSA
Sample image of anodized porous surface A1050
Voltage 20V Current density 15mA/cm2
Temperature 18°C
aluminum foil 47μm
adhesive tape 70μm
Luminescence signal spectrum of PSA on porous A1050
■ Aluminum tape attached to carbon fiber wing, anodization provides micro-pores Ø25 to 40nm
■ 1.96% to 5% of airfoil thickness added locally to wing geometry
Experimental setup: AA-PSP
Steimle - Experimental investigation of transonic fluid-structure interaction phenomena at a high aspect ratio swept wing 7
wing model
Optical setup for AA-PSP measurements at the test section side wall
○ UV-light source flicker-free mercury vapor lamp Osram HBO 500W with band pass filter Schott UG-11 and focusing lens
○ Images recorded with Photron Fastcam 1024 PCI CMOS device with Leica Noctilux M 1:1/50mm lens and band pass filter combination Schott KV-408 + Lee V28 Blueberry 8
○ Images acquired at fs = 1.5 and 2kHz
○ Camera set in Scheimpflug condition to focus entire wing surface
Experimental setup: AA-PSP
Steimle - Experimental investigation of transonic fluid-structure interaction phenomena at a high aspect ratio swept wing 8
Instantaneous distribution of PSA luminescence intensity corresponding to the local pressure on the upper wing surface, image acquisition rate fs = 1500 Hz
[α0 M∞] = [0°,0.86]
Fixed wing aerodynamics: Weak supersonic field
Steimle - Experimental investigation of transonic fluid-structure interaction phenomena at a high aspect ratio swept wing 9
Time-resolved pressure distribution on wing upper surface from AA-PSP with a-priori calibration, image acquisition rate fs = 1500 Hz [α0 M∞] = [0°,0.86]
1
0.5
0
-0.5
-1
-1.5
cp
Fixed wing aerodynamics: Weak supersonic field
Steimle - Experimental investigation of transonic fluid-structure interaction phenomena at a high aspect ratio swept wing 10
Aluminum foil causes slight change in time-averaged pressure distribution
Weak and highly dynamic shock wave in η = 0.286
Strong fluctuations in shock position and strength
Fixed wing aerodynamics: Weak supersonic field
Time-averaged pressure distribution on wing upper surface from AA-PSP with a-priori calibration, image acquisition rate fs = 1500 Hz
Steimle - Experimental investigation of transonic fluid-structure interaction phenomena at a high aspect ratio swept wing 11
Skewing of the boundary layer velocity profile in the rear of the wing
Incipient separation in the shock foot region
Time-averaged pressure distribution and pressure fluctuation quantities
Fixed wing aerodynamics: Weak supersonic field
Surface flow pattern on wing upper side
Skin friction line
Separation line
separation
Steimle - Experimental investigation of transonic fluid-structure interaction phenomena at a high aspect ratio swept wing 12
Spectral analysis of oblique shock parameters
■ Shock buffet at ω* = 0.72 ■ Marginal separation acts as
sound source due to shedding of vortex structures at the sharp TE
■ Buffet originates from sensitivity of weak shock wave to sound waves travelling upstream
0 0.5 1 1.5 2 2.5-12-11-10-9-8-7-6-5-4-3-2
® s
ω*lo
g 10(|x
′ /c1|2 /f s [1
/Hz]
) [1/
Hz]
0 0.5 1 1.5 2 2.5-12-11-10-9-8-7-6-5-4-3-2
®
ω*
log 10
(|(p 2/p
1)′ |2 /f s [1
/Hz]
) [1/
Hz]
0 0.5 1 1.5 2 2.5
-9-8-7-6-5-4-3-2-101
ω*
log 10
(|β′ |2 /f s [1
/Hz]
) [1/
Hz]
0 0.5 1 1.5 2 2.5-10-9-8-7-6-5-4-3-2-10
® µ
ω*lo
g 10(|θ
′ |2 /f s [1/H
z]) [
1/H
z]
Fixed wing aerodynamics: Weak supersonic field
■ Weak SBI test case for harmonic forcing experiments
Steimle - Experimental investigation of transonic fluid-structure interaction phenomena at a high aspect ratio swept wing 13
1
0.5
0
-0.5
-1
-1.5
cp
Fixed wing aerodynamics: Strong supersonic field
Time-resolved pressure distribution on wing upper surface from AA-PSP with a-priori calibration, image acquisition rate fs = 1500 Hz [α0 M∞] = [0°,0.92]
Steimle - Experimental investigation of transonic fluid-structure interaction phenomena at a high aspect ratio swept wing 14
Aluminum foil causes slight displacement of time-averaged shock position downstream
Strong shock wave with λ-configuration in η = 0.286
Flow field dynamics focused on area of shock wave
Time-averaged pressure distribution on wing upper surface from AA-PSP with a-priori calibration, image acquisition rate fs = 1500 Hz
Fixed wing aerodynamics: Strong supersonic field
Steimle - Experimental investigation of transonic fluid-structure interaction phenomena at a high aspect ratio swept wing 15
Skin friction line
Separation line Outer stream line
■ Shock-induced full scale TE separation ■ Performance boundary of this
configuration
separation
Surface flow pattern on wing upper side
Time-averaged pressure distribution and pressure fluctuation quantities
Fixed wing aerodynamics: Strong supersonic field
Steimle - Experimental investigation of transonic fluid-structure interaction phenomena at a high aspect ratio swept wing 16
■ Shock oscillation at ω* = 0.73 and higher harmonics
■ Still distinct oscillation in flow deflection due to pulsation of separated area
■ No fluctuation with ω* = 0.42!
Spectral analysis of oblique shock parameters
0 0.5 1 1.5 2 2.5-12-11-10-9-8-7-6-5-4-3-2
ω*lo
g 10(|x
′ /c1|2 /f s [1
/Hz]
) [1/
Hz]
0 0.5 1 1.5 2 2.5-12-11-10-9-8-7-6-5-4-3-2
ω*
log 10
(|(p 2/p
1)′ |2 /f s [1
/Hz]
) [1/
Hz]
0 0.5 1 1.5 2 2.5
-9-8-7-6-5-4-3-2-101
®
ω*
log 10
(|β′ |2 /f s [1
/Hz]
) [1/
Hz]
0 0.5 1 1.5 2 2.5-10-9-8-7-6-5-4-3-2-10
®
ω*lo
g 10(|θ
′ |2 /f s [1/H
z]) [
1/H
z]
Fixed wing aerodynamics: Strong supersonic field
■ Strong SBI test case for harmonic forcing experiments
Steimle - Experimental investigation of transonic fluid-structure interaction phenomena at a high aspect ratio swept wing 17
Harmonic forcing experiments: Weak interaction test case
Amplitude effect on 1st harmonic pressure distributions on upper surface in η = 0.286
■ Distinctive harmonic response of the shock wave ■ Reduction of flow field response with increasing amplitude
Steimle - Experimental investigation of transonic fluid-structure interaction phenomena at a high aspect ratio swept wing 18
Harmonic forcing experiments: Weak interaction test case
Frequency effect on 1st harmonic pressure distributions on upper surface in η = 0.286
■ Strongest flow field response on heaving wing at smallest frequency
■ Significant reduction with increasing frequency
Steimle - Experimental investigation of transonic fluid-structure interaction phenomena at a high aspect ratio swept wing 19
Harmonic forcing experiments: Strong interaction test case
Amplitude effect on 1st harmonic pressure distributions on upper surface in η = 0.286
■ Strong shock configuration generally more sensitive to structural motion due to harmonic motion of the separation line in phase with the wing oscillation
Steimle - Experimental investigation of transonic fluid-structure interaction phenomena at a high aspect ratio swept wing 20
Harmonic forcing experiments: Strong interaction test case
Frequency effect on 1st harmonic pressure distributions on upper surface in η = 0.286
Steimle - Experimental investigation of transonic fluid-structure interaction phenomena at a high aspect ratio swept wing 21
Harmonic forcing experiments: Strong interaction test case
■ Fluid structure energy exchange determines the development of aeroelastic instabilities potentially occurring in cruise flight conditions
■ Averaged local energy exchange estimated based on the time-resolved pressure and synchronously measured wing motion data in η = 0.286
■ Work coefficient cw describes the work of a fluctuating pressure cp‘(t) exerted on a wing surface element dAi corresponding to the normal vector n
Steimle - Experimental investigation of transonic fluid-structure interaction phenomena at a high aspect ratio swept wing 22
Local energy exchange: Weak SBI flow
Time-averaged work coefficient in η = 0.286 on the upper surface,
weak interaction flow
■ Weak shock wave present at decreasing aeroelastic stability boundary
■ Amplification of excitatory effect of the fluid-structure interaction
■ Cross-flow region in the rear of the wing illustrates damping nature of boundary layer flow with skewed velocity profile
■ Heave amplitude effect would have general potential to drive destructive flutter amplitude increase at pure bending motion
■ Structural excitation reduced when pitch DOF is activated and heave DOF suppressed
Steimle - Experimental investigation of transonic fluid-structure interaction phenomena at a high aspect ratio swept wing 23
Time-averaged work coefficient in η = 0.286 on the upper surface, strong interaction flow
Local energy exchange: Strong SBI flow
Steimle - Experimental investigation of transonic fluid-structure interaction phenomena at a high aspect ratio swept wing 24
Summary
● Results from experimental test campaign with supercritical high aspect ratio swept wing can be used to analyze unsteady transonic flow behavior
● Single shock wave with incipient separation close to trailing edge: highly dynamic flow with self-induced periodic shock oscillation
● Lambda shock system with full scale 3D separation: lower level of unsteadiness, but still with active acoustic feedback mechanism; unsteadiness reduced by steady character of the separation line
● Development of shock wave motion along the wing span shows synchronous shock motion in the inner halfspan region
● Trailing edge kink region identified as major source of disturbances with ω* = 0.72
● AA-PSP is a valid measurement tool for this unsteady flow, despite the high noise level contained in the images as result of weak dynamic intensity signal
● AA-PSP coating able to visualize the unsteady pressure field with high degree of reliability regarding frequencies contained in the dynamic flow process
● Experiments were performed within the Collaborative Research Center SFB 401 of the German Research Foundation (DFG)
Steimle - Experimental investigation of transonic fluid-structure interaction phenomena at a high aspect ratio swept wing 25
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