53rd 3AF International Conferenceon Applied Aerodynamics26 – 28 March 2018, Salon de Provence – France

FP51-2018-simiriotis

Electroactive morphing on a supercritical wing targeting improvedaerodynamic performance and flow control in high Reynolds numbers

N. Simiriotis(1), G. Jodin(2), A. Marouf(3), Y. Hoarau(4), J.F. Rouchon(5) and M. Braza(6)

(1)IMFT UMR 5502, 2 Alle du Professeur Camille Soula, 31400 Toulouse, France, nikolaos.simiriotis@imft.fr(2)LAPLACE UMR 5213/IMFT UMR 5502, 2 rue Charles Camichel, 31071 Toulouse, France, jodin@laplace.univ-tlse.fr

(3)ICUBE UMR7357/IMFT UMR 5502, 300 Bd Sebastien Brant, 67400 Strasbourg, France, abderahmane.marouf@etu.unistra.fr(4)ICUBE, UMR7357, 300 Bd Sebastien Brant, 67400 Strasbourg, France, hoarau@unistra.fr

(5)LAPLACE, UMR 5213, 2 rue Charles Camichel, 31071 Toulouse, France, rouchon@laplace.univ-tlse.fr(6)IMFT, UMR 5502, 2 Alle du Professeur Camille Soula, 31400 Toulouse, France, marianna.braza@imft.fr

ABSTRACT

This article examines the morphing effects of the trailing-edge deformation and vibration on the turbulent struc-tures in the wake of a supercritical Airbus-320 wing. TheReynolds number was 1 Million. The study is carriedout in the low subsonic regime at an incidence angle of10o, corresponding to take-off/landing flight phases. Themorphing effects on the aerodynamic coefficients are dis-cussed in order to identify optimal frequency/amplituderanges for the vibrations imposed by composite piezo-actuators, disposed along the span of the wing. Time-Resolved PIV measurements taken from the subsonicwind tunnel are investigated together with numerical sim-ulations. Morphing effects on the coherent structures inthe wake have been analysed by means of Proper Orthog-onal Decomposition. It has been shown that specific fre-quency/amplitude ranges are able to produce an enhancedaerodynamic performance and suppress instability modesassociated with noise sources.

1. INTRODUCTION

This study aims at completing previous studies carriedout at the Institut de Mecanique des Fluides de Toulouse- IMFT that highlight the capacity of morphing to in-crease lift, decrease drag and reduce the amplitude of in-stability modes associated to aerodynamic noise. Morph-ing from hereby after will be referring to the adaptationof the real-time shape and vibrational behaviour of theaerodynamic surface. In this context, a multi-disciplinary

research platform involving the LAPLACE (LaboratoirePlasma et Conversion d’Energie) and IMFT French Lab-oratories has been continuously working in this topicsince 2010, originally thanks to the support of the Foun-dation STAE (http://www.fondation-stae.net/). By thissynergistic platform among six Institutes in Toulouse(www.smartwing.org) coordinated by IMFT and in closecollaboration with AIRBUS Emerging Technologies andConcepts Toulouse, advanced electroactive morphing de-signs for the wings of the future are currently being de-veloped and studied (https://lejournal.cnrs.fr/videos/les-ailes-du-futur). In particular, the hybrid morphing con-cept, partly bio-inspired, was developed ([11], [8]) tooperate at different time scales. This concept enablesthe manipulation of the near-region turbulence enhanc-ing specific beneficial structures in the wake. In this wayand thanks to the introduction of smaller-scale chaoticturbulent vortices, breaking down or suppression of pre-existing predominant instability modes can be achieved.Activating a shear sheltering effect leading to a consider-able thinning of the separated shear layers, it has beenrendered possible to increase the aerodynamic perfor-mance and simultaneously decrease the noise sources.

This study focuses in high Reynolds number (order of106). Previous studies in the literature were carried out atlow Reynolds numbers [7], [15] examined part of the flowcharacteristics and although useful in the analysis, arequite limited and not operating in multiple scales. Pastpapers have also examined the forcing of the trailing ofa wing [4] also in lower Reynolds number. The flow inthe supercritical Reynolds range presents complex vortex

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dynamics and interactions with the solid structure, call-ing for specific attention in order to produce successfulmorphing effects. High Reynolds dynamics change thegeneral flow behaviour and the morphing practices andtargets. In the present context, the electro-active morph-ing is a more general strategy than standard flow con-trol techniques as it creates fluid-structure interactionsand inter-optimality among structural dynamics and tur-bulence manipulation.

In the present article, the electroactive morphing ef-fects around an A320 wing are presented at a Reynoldsnumber of 1 million and an angle of incidence of 10o, bymeans of numerical simulation and experimental investi-gation.

2. EXPERIMENTAL PROCEDURE

The present article follows the experimental work of G.Jodin [8] on a reduced scale hybrid morphing prototypeembedding both camber control and Higher FrequencyVibrating Trailing Edge (HFVTE) actuators. Measure-ments for a Reynolds number of 1 million are consideredto provide an inter-validation between the experimentaland the numerical studies following. In this analysis, theelectroactive morphing effects of the higher frequency vi-bration and slight deformation of the Multi-Fiber com-posite piezo-actuators in the trailing edge region (Fig. 1)will be studied. The piezoelectric patches were glued onboth sides of a metallic substrate and are alternativelyactivated to reach deformations with amplitudes up to0.5mm. In order to maintain the trailing edge shape, theassembly is covered by silicone, specifically designed tolimit the impact on the actuator’s performance. The tech-nical characteristics for the electro-active hybrid morph-ing actuation are extensively described in [9]

At a given controlled camber, the vibrating trailingedge creates small-scale turbulent eddies and adds ki-netic energy in the wake that provokes interactions inthe upper and lower shear layer. This aims at enhancingthe super-critical character of the flow and producing aneddy-blocking effect constricting the shear layers as men-tioned in [8]. By enriching this region with chaotic vor-tices, the target is to attenuate specific coherent structuregeneration associated with the wake’s width (form drag),feedback effects on the lift and noise sources. This eddy-blocking concept was first studied numerically in [14] fora transonic flow around a supercritical airfoil and put inevidence experimentally thanks to the electro-active mor-phing [12].

The time Resolved Particle Image Velocimetry (TR-PIV) measurements will be re-examined in this paper.The most probable displacement of the particles betweenconsecutive images is obtained from the cross-correlationplane of consecutive images. The sampling rate wasabout 10KHz. Particle images are recorded during the ex-

Figure 1: Schematic representation of the experimen-tal test section of the S4 wind tunnel of IMFT withthe Airbus-320 wing mounted [8] and illustration of thetrailing-edge piezo-actuators along the prototype’s span[13].

periment using a digital high-speed camera focused in themid-section concerning the depth of the field (the lasersheet representation can be found placed in the stream-wise direction as depicted in Fig. 1). The thickness ofthe laser sheet was 2.5 mm. For the experimental proce-dure smoke particles of 3.4µm diameter were introducedin the airflow giving a Stokes number Sk = 5 ·10−4 whichallows the particles follow consistently the motion of thefluid.

The wing with a chord dimension of 0.7m was placedat an incident angle of 10o. The incoming velocity washeld constant at (21.5m/s), which for reference valuesof temperature (293K) and pressure (101325Pa) corre-sponds to a (chord) Reynolds number of 1 million. Thevelocity variation was evaluated over multiple experi-ments was estimated to be below 1.5% while the blockageratio was found to be acceptable as long as the focus isthe relative effects of the morphing application. The tur-bulence intensity of the inlet section of the wind tunnelwas estimated at about 0.1% of the free stream velocity.The experimental benchmark was also equipped with anaerodynamic balance in order to measure the lift and dragforces. A more detailed description of the experimentalequipment and procedure can be found to [8].

3. NUMERICAL APPROACH & TURBU-LENCE MODELLING

The complete time dependent compressible Navier-Stokes equations have been solved under the conserva-tive form using the Navier-Stokes Multi-Block (NSMB)code [6], in both two and three dimensions. The com-putational domain is subdivided into a number of quadri-lateral (2D) and hexahedral (3D) grid cells resulting in a

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(a) Multi block description of the computational domain.

(b) 3D surface meshing of theA320 wing.

(c) 2D mesh around the A320wing.

Figure 2: Computational domain and mesh.

structured mesh. The multi-block strategy is followed inaccordance to the parallelization procedure of the code.A separate discretization of the equations in space andtime is applied.

Finite volume cells of constant size in time are con-sidered for the discretization in space. A fourth orderstandard central skew-symmetric spatial scheme with ar-tificial second and fourth order dissipation terms wasused for the convection terms and a second-order cen-tral scheme for the diffusion terms. For the temporal dis-cretization, dual time-stepping with a second order im-plicit backward difference scheme is performed [5]. Theartificial compressibility method was implemented in thepreconditioning of the flow to increase accuracy in thelow subsonic regime.

Both 3D and 2D meshes (Fig. 2) were developed. Forthe standard 2D mesh, about 300000 finite volume cellswere added to the computational domain. The respective3D mesh was a simple extrusion of the initial 2D mesh inthe third dimension, constructed by adding points in thespan-wise direction leading to a total mesh size close to10 million. A refined version of the 2D mesh was alsotested. Theses grid sizes were selected after thorough nu-merical studies. The physical time-step was kept constantin all the computations at 10−5 giving a CFL numberaround 50. About 60− 80 inner iterations were carriedout for each time-step.

The upper and lower walls of the tunnel were consid-ered by means of non-slip and slip boundary conditions.After numerical tests that indicated no considerable ef-fect due to the respective boundary layers on the wakedevelopment, they have been given a no-slip condition.The inlet velocity was held constant at 21.5m/s with aturbulence intensity of 1% to establish matching levels ofturbulence with the experimental setup.

In the present work the Organized Eddy Simulation(OES) approach [2], [14] has been employed. Based

on the ensemble (phase) averaging of the flow, this ap-proach is sensitized to allow coherent structures and theirrelated instabilities to develop in the high Reynolds num-ber range and is well adapted for detached flows, bothtypical of all aeronautical applications. The OES ap-proach is non-inherently 3D and therefore can be appliedin 2D simulations with sufficient accuracy in capturingthe main coherent structure dynamics and their modifica-tion. Therefore, it provides a robust method for capturingphysical phenomena and treating near wall turbulence. Amore detailed description of the OES can be found in [2]and [14].

4. EXPERIMENTAL STUDY - TRPIV

Fig. 3 presents the instantaneous velocity field measuredby means of TRPIV, with the contribution of the Signaland Image processing service of IMFT (S. Cazin and M.Marchal). The post-processing of the raw PIV resultswas carried out with the CPIV-IMFT software, developedwith the contribution of the software services of IMFT (P.Elyakime) for parallel (MPI) post-treatment of the resultsin supercomputing architectures. The plane section de-picted in this figure corresponds to the laser sheet placedin the mid-span region.

Figure 3: Instantaneous stream velocity from the TRPIVmeasurements, visualizations by streaklines for Re= 1M,angle of attack ao = 10o.

Temporal signals of the vertical velocity componenthave been extracted in selected positions downstreamof the trailing edge and the corresponding Fast FourierTransform (FFT) on these signals provide the turbulencespectra. Plots of the Power Spectral Density are presentedin Fig. 4b and Fig. 4c for two points selected in the nearwake region (see Fig. 4a).

The predominant frequency bump shown in these spec-tra corresponds to the shear layer’s vortex emission, acoherent pattern smeared by chaotic turbulence motion.The characteristic frequency of the shear layer instabil-ity is found to be at 254Hz as indicated by the signalacquired from monitor point 2. This primary instabilityis a result of the interactions between the lower and up-per shear layers. The vortex shedding developed further

3

(a) Position of the selected monitor points along the wake;the trailing edge is noted with a symbol.

100

102

f (Hz)

-40

-30

-20

PS

D o

f W

static

254 Hz

(b) Spectrum from monitorpoint 2.

102

f (Hz)

-50

-40

-30

PS

D o

f W

static

X: 169.2

Y: -28.23

170 Hz

(c) Spectrum from monitorpoint 4.

Figure 4: Spectral content of the vertical velocity compo-nent in the near wake region from TRPIV results.

downstream takes place at frequencies around 170Hz.The monitor point 4 is placed just below the wake in orderto give a clear indication of the vortex shedding patternwhich is analysed in more detail by means of the numer-ical simulation because as it is more pronounced in thedownstream areas not captured by the PIV plane.

The frequency of the von Karman shedding corre-sponds to a Strouhal number close to 0.34 for a char-acteristic length equal to the initial wake’s width. Thisvalue is in agreement with the respective ones measuredfor circular cylinder in supercritical flow conditions [10].The bumpy image of the spectra indicates non-linear ef-fects between the coherent vortex shedding and the finerscale chaotic turbulent motion. A detailed study of thePIV measurements by a Proper Orthogonal Decomposi-tion (POD) is included in [8] and allows distinguishingthe coherent from the chaotic effects.

5. NUMERICAL STUDY

The numerical simulations have been carried out respect-ing the afore mentioned experimental conditions. A meshwas constructed depicting faithfully the geometry of testsection. In this section, the stream-wise direction for thecomputations is the orientation of the x axis and the ver-tical direction is that of the z axis, leaving y axis alongthe span-wise direction. For the validation of the staticcase, the 3D and the two version of the 2D mesh wereused while for the morphing tests, only the standard 2Dmesh is considered as it is proven more efficient in terms

(a) Surface pressure and y vorticity component on aplane section; the rectangular represents the plane ofthe PIV measurements for which all the comparisonswill take place.

(b) Averaged stream velocityclose to the leading edge.

(c) Averaged stream velocityclose to the trailing edge.

Figure 5: Global view of the predicted flow field bymeans of numerical simulation for Re = 1M, angle of at-tack ao = 10o.

of computational cost for an extensive multi-parametricstudy.

Fig. 5 provides a global view over the computationaldomain and the solution acquired by means of numericalsimulation. The flow coming from the inlet moves down-stream (from left to right from hereby after). A smalldetachment at the trailing edge of the wing is evident(Fig. 5c) resulting to the unstable wake region followingright after.

The comparison for the time averaged velocity profilesis depicted in Fig. 6a. The agreement between the mea-sured and computed profiles is quite good, even for the2D case presented in this figure. In Fig. 6b and 6c a com-parison between the various numerical tests and the ex-periments is presented. The calculation for the displace-ment and momentum thickness in the wake follows eq. 1and 2, where u99% = 0.99 ·Uinlet and z∗99% the vertical po-sitions along the wake where this is achieved.

δ∗ =

∫ zup99%

zlow99%

(1− uu99%

)dz (1)

θ =∫ zup

99%

zlow99%

uu99%

(1− uu99%

)dz (2)

The agreement between the experimental data and the

4

(a) Averaged axial velocity profiles; comparison be-tween the standard 2D simulation and the experimen-tal results; trailing edge noted with a symbol.

1 1.5 2

x/c

0

0.01

0.02

0.03

0.04

*/c

STATIC

STATIC REFINED

STATIC 3D

STATIC EXPE

(b) Dispalcement thickness.

1 1.5 2

x/c

0

0.005

0.01

0.015

/c

STATIC

STATIC REFINED

STATIC 3D

STATIC EXPE

(c) Momentum thickness.

Figure 6: Quantitative comparison of the computationaltest with the TR-PIV results (STATIC EXPE); numericaltests for: standard 2D mesh (STATIC), a refined 2D mesh(STATIC-REFINED), a 3D mesh (STATIC 3D).

computational results is quite satisfactory. Fig. 7 atteststo this as well. It is evident that the main dynamics in-volved in the wake development can be accurately cap-tured even by the standard 2D mesh. The width of thespectral bump is well captured both close to the trailingedge (primary instability) and further downstream in thewake where the shedding is fully developed (secondaryinstability). The vortex structure dynamics and their non-linear interactions can be visualized using streaklines inthe wake, pictured in Fig.7a. The unstable shear layer de-velops global predominant frequencies (around 220Hz)close to the trailing edge. The lower and upper shear lay-ers interact with each other yielding a von Karman vortexstreet further downstream. The vortex shedding is placedaround 165Hz− 185Hz, which compares well with thevalue obtained from the experiments. These effects arealso highlighted by the POD performed on the computa-tional results.

5.1 Electroactive Morphing on the TrailingEdge

The motion and slight deformation of the near-trailingedge region due to the 4mm long MFC piezo-actuatorsvibrating with an amplitude of order 0.5mm. The Arbi-

(a) Position of the monitor points in the computational do-main along the wake.

102

f (Hz)

-101

PS

D o

f W

CFD

EXPE

(b) Spectrum from monitorpoint 5.

100

f (Hz)

-101

PS

D o

f W

CFD

EXPE

(c) Spectrum from monitorpoint 6.

Figure 7: Streaklines (top) and spectral content (bottom)of the near wake region, comparison between computa-tional (standard 2D mesh) and experimental results.

trary Lagrangian-Eulerian methodology [3] is applied forthe calculation of the variables in the deformable/movinggrid. The applied deformation in the trailing edge regionfollows closely the polynomial deformation applied onthe reduced scale prototype. The frequency of the vibra-tion fa and the amplitude Ao of the sinusoidal time vari-ation are left to be imposed in each test case. The ampli-tude corresponds to the maximum displacement, i.e. thedisplacement of the ending tip of the trailing edge. Inthe tests following, the effect of the aerodynamic forceson the vibrational behaviour of the piezoactuators has notbeen taken into account (one-way fluid-structure interac-tion) since they have been evaluated as negligible in [9].

- EFFECTS ON THE WAKE DYNAMICS

The morphing seems to have prominent effects on thedevelopment of vortical structures in the wake as exhib-ited in Fig. 8 where visualizations by streaklines are pre-sented, in comparison with Fig. 7a where no morphingwas applied. The amplitude of the vibration was heldconstant at 0.35mm while the actuation frequency wasleft to vary. In the experiments this amplitude value wasthe largest one tested with the specific morphing imple-mentation. For frequencies lower than the one related tothe shear layer instability, the flow seems unaffected bythe perturbation travelling at a much lower propagationspeed. For an actuation close to the instability frequency( fa = 200Hz), some kind of resonance phenomena seemto take place. A ”lock-in” to the morphing frequency is

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(a) fa = 60Hz

(b) fa = 200Hz

(c) fa = 300Hz

Figure 8: Development of vortical structures in the wake,visualization with streaklines, calculation my means ofnumerical simulation. The amplitude is set at 0.35mm forevery actuating frequency.

achieved, non-linear interactions seem to be suppressedand large coherent highly energetic structures are devel-oped resembling clearly a vortex sheet. When the mor-phing frequency further increases ( fa = 300Hz), the flowseems able to follow the much faster perturbation. The”lock-in” mechanism remains (only to become weakerfor even higher frequencies) and smaller vortices get gen-erated resulting to a much thinner wake region. The shearlayer seems to be enforced and a convective instabilityleads to the suppression of the shedding mechanism up tofurther downstream.

- MEAN EFFECTS ON THE WAKE

In this section a comparison on the time averaged re-sults is carried out. In Fig. 9 the mean axial velocity pro-files are plotted along the wake for various x/c positions,where the x axis is zero at the leading edge of the wing.It is evident that for frequencies lower than the naturalones of the flow (i.e. for 60Hz and 100Hz) only slight

changes in the profiles are visible and mostly at the earlyx/c stations, close to the trailing edge. For an actuationfrequency close to the natural frequency gets slightly dis-placed at a lower height and get wider. For higher fre-quencies, a much thinner wake is visible. As the shed-ding is suppressed up to further downstream positions,the upper and lower shear layers do not spread as much.

−0.25

−0.2

−0.15

−0.1

−0.05

0

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1

Z/c

U−

/U∞

STATIC

60 Hz

100 Hz

200 Hz

300 Hz

300 Hz − LA

(a) x/c = 1.1

−0.25

−0.2

−0.15

−0.1

−0.05

0

0.6 0.7 0.8 0.9 1 1.1

Z/c

U−

/U∞

STATIC

60 Hz

100 Hz

200 Hz

300 Hz

300 Hz − LA

(b) x/c = 1.4

−0.25

−0.2

−0.15

−0.1

−0.05

0

0.6 0.7 0.8 0.9 1 1.1

Z/c

U−

/U∞

STATIC

60 Hz

100 Hz

200 Hz

300 Hz

300 Hz − LA

(c) x/c = 1.7

−0.25

−0.2

−0.15

−0.1

−0.05

0

0.6 0.7 0.8 0.9 1 1.1

Z/c

U−

/U∞

STATIC

60 Hz

100 Hz

200 Hz

300 Hz

300 Hz − LA

(d) x/c = 2.0

Figure 9: Comparison of mean longitudinal velocity pro-files along the wake for various actuating frequencies.The amplitude is set at 0.35mm for every morphing appli-cation, except for the 300Hz-LA (lower amplitude) casewhere a value of 0.15mm was used.

Fig. 10 attests to this effect. The values for the wakewidth and for the spreading rate of both shear layers arepresented. The spreading rate here is defined with thedistance for which the halving of the velocity is achieved(z∗50%). In Fig. 10a the thinning of the wake is pre-sented due to the suppression of the shedding. Increas-ing the frequency to even higher values (i.e. 370Hz)seems to weaken this shedding delay. Fig. 10b exhibitsthe decrease of the spreading of the upper shear layerwhich gets overpowered by the strengthened lower one,the interactions become weaker and finally the resultingshedding mechanism is delayed as it has been previouslyshown.

- EFFECTS ON THE AERODYNAMIC FORCES

The effect on the aerodynamic forces is evaluated inthis section. The lift and drag coefficients are comparedin Fig. 11. In Fig. 11a and 11b the effect of the actua-tion frequency is presented for a constant amplitude of0.35mm while in Fig. 11c and 11d the effect of the am-plitude is examined.

Actuating in the region around the natural sheddingfrequency presents a prominent increase in both lift anddrag mean values, accompanied however with a signifi-cant increase in the fluctuations (as indicated by the root

6

(a)

(b)

Figure 10: Comparison of the wake characteristics forvarious actuating frequencies. (a) Width of the wake withb95% = zup

95%−zlow95%, z∗95% the position for which u= 0.95 ·

Uinlet and (b) Spreading rate of upper (Sup) and lower(Sbottom) shear layer. The amplitude is set at 0.35mm forevery morphing application besides the 300Hz-LA (loweramplitude) case where a value of 0.15mm was used.

mean squared - rms - values) of the coefficients as well.This attests to the resonance observed in the previous sec-tion and is also in agreement with the experimental stud-ies included in [4]. Acting with frequencies outside thisregion still provides an increase in lift and in some casesa decrease in drag, but always keeps the rms levels inlower values. In all the morphing cases the lift versusdrag ratio increases, an effect that could not achieved witha static deformation of the trailing edge at the maximumdisplacements.

The amplitude variation indicates a linear responseconcerning the rms values which increase with the am-plitude. The lift coefficient always increases while thedrag coefficient initially decreases and then starts to in-crease. After a specific amplitude, the value of the drag ispractically constant for the amplitudes examined in thisarticle. Whether this plateau is higher or lower than theinitial drag value without morphing depends on the fre-

quency of the actuation.

(a) Lift coefficient (b) Drag Coefficient

(c) Lift coefficient (d) Drag Coefficient

Figure 11: Effect on the aerodynamic coefficients ver-sus frequency (top) variations with a constant amplitudeof 0.35mm and versus amplitude (bottom) for a constantfrequency of 300Hz (left) and various frequencies (right).Zero values for amplitude/frequency imply absence ofmorphing.

5.2 Proper Orthogonal Decomposition

The Proper Orthogonal Decomposition (POD) is appliedhere for the eduction and study of the coherent structuresdeveloped in the flow. The POD method was introducedfirst by Karhunen and Loweve and applied in Fluid Me-chanics by Berkooz et al. [1]. The flow field solution issplit in spatial modes and temporal coefficients sorted bytheir importance (relative energy) in the flow.

The Snapshot POD is applied here on the computa-tional results for the two components of the velocity field.In this way there is a direct correspondence between theeigenvalues provided by the method and the kinetic en-ergy of the flow. Two cases are examined here: the staticone where no morphing is applied and the actuation at300Hz where we have the most prominent effects in thewake development. In both cases the sampling time stepwas taken constant (10−4sec) and a constant number ofsnapshots (619) were used to construct the POD data ma-trix.

In Fig. 12a the mode eigenvalues are plotted for the twocases. The first mode corresponding in the mean flow, ex-hibits the highest values as it represents the biggest por-tion of the flow’s kinetic energy. Taking into account themodes corresponding to the fluctuating part of the flow(Fig. 12b) it can be deduced that less than 60 modes cover98% of the fluctuating energy. The energy levels of the

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first few fluctuating modes are increased in the morphingcase and the slope of the cumulative fluctuating energy isreduced. While the energy of the first (mean) modes isin the same level (less than 1% difference) between thetwo cases, the total fluctuating energy is significantly in-creased in the morphing case.

10 0 10 1 10 2 10 3

modes

10 -4

10 -2

10 0

10 2

10 4

10 6

eig

en

va

lue

STATIC

300 Hz

(a) Sorting of eigenvalues. (b) Relative fluctuating energy.

Figure 12: Eigenvalues of the modes sorted by themethod (left) and relative cumulative energy (right) cor-responding to the fluctuating part of the flow.

The spatial image of the modes as well as their tem-poral behaviour is significantly different between thetwo cases. For the case where no morphing is applied(Fig. 13), the modes 2 (coupled with mode 3) and 4 (cou-pled with mode 5) correspond to the shedding and ini-tial instability respectively, observed also in the spectra.Mode 6 presents modulations of the shedding due to non-linear interactions. Higher modes (not presented here)correlate with modulations and low frequency feedbackeffects. Mode 27 indicates the shear layer instability pat-tern. A frequency close to 350Hz is also identified in thesame region and could be related to a separation bubblecreated on the pressure side, close to the trailing edge, dueto the (supercritical) shape of the A320 wing. Modes ofeven higher order (above 50) are related to smaller scalefluctuations over the wake.

Considering the morphing case (Fig. 14) the followingmodifications are present. Mode 2 (coupled with mode3) corresponds to the reinforcing of the shear layer closeto the trailing edge. The temporal coefficient presents adevelopment locked at the actuating frequency (300Hz)while the spectrum of mode 4 (coupled with mode 5)related to the secondary instability takes place at a fre-quency with half of this value. In this case, the vonKarman shedding seems to be contained only furtherdownstream and to a less wide region as the wake be-comes thinner as well. Modulations of the instabilitiesoccur, indicating a move to different frequency ranges(mode 6) while harmonics of the actuation frequency ap-pear as well causing further interactions. In mode 41,a structure resembling the one of mode 27 of the non-morphed case appears. As the energy of the fluctuationsincreases, previous modes are shifted in regions of rela-tively lower order. The predominant higher frequency at350Hz appearing previously has vanished.

6. CONCLUSION

In this study the electroactive morphing effect createdby mini-piezo-actuators disposed along the span of anAirbus-A320 wing has been studied by means of TRPIVand High-Fidelity numerical simulations. These actua-tors introduce optimal vibrations and slight deformationsof the trailing-edge region. Having in disposal a detailedexperimental database and newly acquired computationalresults, a combined examination of high Reynolds dy-namics in the wake of this supercritical wing has beencarried out in respect of aerodynamic performance in-crease. The main flow characteristics have been under-lined. Various frequencies and amplitude combinationshave been studied numerically to evaluate the morphingeffects in order to enable future experiments around thesame prototype, focusing on the most optimal morphingactuations.

The wake dynamics are significantly affected by theapplication of morphing when acting in frequencies closeor above the natural frequencies of the separated shearlayers. This has been emphasized by the POD analy-sis that has showed new modes emerging and taking theplace of naturally existing modes in positions of higherrelative energy. The aerodynamic performance gets en-hanced as the mean value of the lift versus drag is foundto be increased in every morphing case examined. By thepresent electroactive morphing concept, an order of 3.2%increase in lift has been achieved and at the same time a1% decrease in the drag. Some frequencies studied pro-vided even higher values of drag reduce. This enhance-ment of the aerodynamic performance was completely as-sociated with the vibratory behaviour as slight static de-formations of the trailing edge by the same amplitude didnot produce analogous results.

ACKNOWLEDGEMENTS

The authors are grateful to the Engineering and Techni-cal services of IMFT and LAPLACE Laboratories, to theSignal and Image Services of IMFT enabling the TR-PIV measurements, to the Software Services of IMFTenabling the MPI treatment of the TRPIV data bases onthe supercomputer CALMIP, as well as to the three na-tional supercomputing centers: CINES, IDRIS, CALMIPfor having provided a significant CPU allocation for thepresent study.

REFERENCES

[1] G Berkooz, P. Holmes, and and J. L. Lumley. TheProper Orthogonal Decomposition in the Analysisof Turbulent Flows. Annual Review of Fluid Me-chanics, 25(1):539–575, 1993.

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(a) U2 (b) W2 (c) a2

(d) U4 (e) W4(f) a4

(g) U6(h) W6 (i) a6

(j) U27 (k) W27 (l) a27

Figure 13: Spatial modes computed with the POD corresponding to the two velocity components and FFT of the respectivetemporal coefficients. Indices provide the order of the mode. The first (mean) mode is omitted. Case without morphing.

[2] R. Bourguet, M. Braza, G. Harran, and R. El Ak-oury. Anisotropic Organised Eddy Simulation forthe prediction of non-equilibrium turbulent flowsaround bodies. Journal of Fluids and Structures,24(8):1240–1251, November 2008.

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(a) U2 (b) W2(c) a2

(d) U4 (e) W4(f) a4

(g) U6 (h) W6(i) a6

(j) U41 (k) W41(l) a41

Figure 14: Spatial modes computed with the POD corresponding to the two velocity components and FFT of the respectivetemporal coefficients. Indices provide the order of the mode. The first (mean) mode is omitted. Morphing case at 300Hz.

maquette pour l’investigation du morphing lectroac-tif hybride en soufflerie subsonique. pages pp. 1–13,2015.

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N. Simiriotis, G. Jodin, A. Marouf, Y. Hoarau, J.F. Rouchon, M. Braza, Award 3AF « Association d’Aerinautique et Astronautique - France » of best article

presented at the 53th AERO2018 Conference, Salon de Provence, March 2018, Journal of 3AF N° 39, 2019, Page 18,

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