INFORME FINAL PROYECTO FONDECYT

INFORME FINAL
•
C.C3911K`MO 1.4 t HILE
FflNÜCVT
PROYECTO FONDECYT POSTDOCTORADO
3010067
Inicial 3 años ¡ Final 2 años
NUMERO PROYECTO
- DURACIÓN
14.740337-2
Ludovic Bellon
INVESTIGADOR POSTOOCTORADO --
RUT
(2)6784617
Depto. Ingenieria Mecanica, U. De Chile, Bcaucheff 850, Santiago
DIRECCION
FONO
[email protected]
E-mail
CONTENIDO
(NAROUE EL CASILLERO OUE CORRESPONDA)
NO HAY ADJUNTO FUE ENVIADO
riforme Final (en formulario)
X
ublicaciones
X
resentaciones a Congresos
X
valuación del Investigador Patrocinante X
SERA ENVIADO
(FECHA)
)tros (especificar)
Firma InveStgador Patrocinante Firma Investigador Postdoctorado
Fecha: 15/07/2003
1
Santiago. 15 de JUIR) del 2003
Dr. Ludovic Bellon
RUT: 14.740.337-2
Proyecto Fondecyt 3010067
Depto. de Ingencría Mecánica
Beaucheff 850, Santiago
Tel.: (+56 2) 678 4617
Ernail : [email protected]
A
Director Programa Postdoctorado,
FONDECYT
Referencia: Solicitud de término de proyecto
Señor Director,
A través de esta carta, solicito el término anticipado del proyecto de postdoctorado FONDECYT
3010067, a partir del 31 de Julio del 2003. Estoy en efecto seleccionado para un puesto de
encargado de investigación en el CNRS (Centro Nacional de Investigación Científica) en Francia,
con efecto el 1 de octubre del 2003.
Saluda atentamente a usted.
Ludovic Bellon.
ITl QRME 1 INAI. ('ONÇIRS() IONlM(YT - pOSTlx)CTORAIX) - PROYE(R) ()I00(7
Viaje a Francia - Informe cientifico
My visil in Lyon (France) lasE april had several goals, delailled
¡ti
ihe fotlowing 1 ine
1. lresentation of researeh project arid results:
1 ga y e a senhinar on my posidoctoral work ( foctised on (he convection pan) ¡u (he Lahoiatoire de
Physique de l'Ecole Normale Supénieure de Lyon.
2. Complementary rheological measurements:
A deep analysis of the results of the convection expenimenis performed ¡u the laboralory as
limited by nne hig question about the aging 0f (he I..aponite sample we were using how does the
viscosity age with lime for our specific samples ! Viscosity is indeed nne of ihe critica[ propeniy lo
uiiderstand Rayleigh Bénard convection, as it enters the expression of ihe Rayleigh numher i(self
Al¡the other physical properties of ihe samples were studied with (he reseaich facilities oí' the
laboratory. implying the set up of original side experirnents lo measure density, ihermal expatision
coefficient. nr thermal dependance of the optical refraction mdcx... BLIL Ihe study nf viscostty was
no( possihle without specific (and extreinely expensive) aparalus, naniely a high precision
rhenmeter. This research facility was available in ihe Lahoratoire de Physique de lEcole Normale
Supttieure de Lyon, aud gracefuhly lefi al my disposition for a whole rnonth, with all ihe preCioUs
techuical and scienuific help 1 needed lo peiíorm ihese delicate measuremenis. The results of (hese
ineasurements were very usefuli lo interpret the interaction hetween aging and convectioli of nur
samples, and are obviously included in ihe article on convection.
3. Scientific interaction:
The choice of L on. aiid tnaiuly ihe Ecole Normale Supeiieuie, was motivated by lis nuinernus
in my research anca. Duiing this visil. 1 had very nich and enlighting
scientific cornrnunity
conversations with Pr. Beniard Castaing (convection expert). Dr. Sergio Cihiherto (convection and
aging anca). Dr. Jean-Fiançois Pinton (fluid motion). Dr. Artenh Petrosyan (technical aspeci). Pr.
Enic Ft-eyssingea.s (rlieology). Pr. Michel Peyrard (glassy materials), arnong others. The analysis of
my experimental resuhts certaiiily improved a lot with iheir remarks and advices.
1 also liad lile oppontunity lo interact with Pr. Jacques Mugnier, froiri the Lahoratoire des
Maténiaux Luminescents de lUniversité Claude Bernard - Lyon i. Qn sorne side ideas ibat carne
ahong this post doctoral work: we discovered a new way lo make ihin coating films of cohloidal
gels. and wanted to dig furiher in this new technique. The characlerization of such films is a heavy
work, in which Pr. Mugnier has a deep expertise. This firsi contact is very promissing and should
lead tú a fliture cooperation on ihis suhject, wiih certainly sorne inleresting scientific and technical
,esuits in a near futille.
4. Article redaction:
One of ihe author uf the article on convection is Maihieu Gihert. studeni of the Ecole Noiiiiate
Supénieure. Duning a 4 months research training perRxl in our laboratory. ihis french stuchent did a
very mcc work thai produced parl of Ihe results we present ¡u the article oil convection. My visit ¡u
Lyon ailowed us tu ieview the pasi and iecent results together and work oii iheir pubhication.
CONTENIDO DEL INFORME FINAL
1. CUMPLIMIENTO DE LOS OBJETIVOS PLANTEADOS EN EL PROYECTO.
¿Cumplido?
Objetivos
1. Open fiows - design and implementation of:
- Flow visualization technique
- Wake control / vortex generation methods
- Ultrasound scatering technique
2. Open fiows - study of:
- 2 wake control methods
- Coupling vortex shedding / drag, Iift forces
- Generation of vortex wake packets
3. Soft glassy systems - design and realisation of:
- Heat tranfer experiment
- shcar experiment
4. Soft glassy systems - study of:
- Aging properties
- lnstability behavior
- Coupling betwcen aging and flow
Si
Parcial
No
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O
0
O
O
0
O
D
0
O
O
Fundamentación para el cun plimiento parcial o
incumplimiento
Otro(s) aspecto(s) que Ud. considere importante(s) en la evaluación del cumplimiento de los objetivos planteados en la
propuesta original o en las modificaciones autorizadas por los Consejos.
This postdoctoral project was initialy written for 3 years, hut thc cxecution has bccn reduced Lo 2 ycars. as 1 havc just tu-en
elccted for a permanent position in France (starting october 2003). Consequently, the final ohjcctives (quoted aboye)
corrcspond mainly tu thc two first years of the proposal, taking care to respcct thc global coherence of thc project. Let us
note that anyway sorne part of third ycar schedule had already been started, with for example a Faraday wave experirncnt
ready to perform its first measurernents.
The amount of experimental data generated by [he various cxperimcnts of thc project is quite huge, and its analysis is still
in progress at the time of redaction of this final report. We believe that sorne othcr communications could come out of thcse
analysis, and will anyway provide thc basis of a future col laboration betwcen our laboratories in France and Chile.
II. RESULTADOS
Describa brevemente los resultados obtenidos en el proyecto en un máximo de cinco páginas, tamaño carta, espacio
seguido. Para cada uno de los objetivos específicos, describa o resumo los resultados. Relacione las publicaciones y/o
manuscritos enviados a publicación con los objetivos específicos. Incluya en anexos la información de apoyo que estime
pertinente y necesaria para la evaluación.
This projeci is divided in two classes of problems. The first part deals with opens fiows, specifically on
vortex shedding in the wake of a bluff body, whereas the second pan concerns intrinsically out of
equilibrium systems: soft glassy materials. The next unes describe the results of this project in each
direction.
Part 1: Vortex shedding
1.1 Experimental reallzations (Objective 1)
An important part of my activity in the laboratory has been dedicated [o the design and realization of a
few experimental facilities:
• Flow visualization system. For this purpose, a smokc gencrator has becn connected to a fiat array of
100 parallel injectors. The section of the system has been reduced lo the minimum is order to avoid
flow perturbation. A laser light sheet is set in correspondcnce with the smoke plan, to see the details
of flow streamlines iii the wake of the bluff bodies in ihe wind tunnel. Precise alignment of smoke
and light planes is eased with a simple tuning system. This imaging technique allowed us lo illustrate
simply and convincingly the classical hot wire anemometry mea.surements by giving a global view of
the wake. This system is illustrated in AppendixA.I.
• Image acquisition software. Image acquisition is realized with a rapid digital camera. The
commercial software was found to be quite limited in speed acquisition or lcngth of time sequence,
Therefore 1 wrote a horne made software, more efficient and adapted lo our scientific goals (video
sequences or images can be easily imported and analyzed in Matlab for example). Not only was this
realization essential for visualization of wakes in the tunnel, bu( it has been used since in almost ah
the experiments done in the laboratory ! Moreover, the source code of this program is open and
highly documented, which allowed rapid customization to specific requirements of other
experirnents. A siiap shot of the software interface in given in Appendix A.2.
Apart from these specific realizations, ¡ had the opportunity to give my contribution to the design of the
following experimental setup:
• Fiat plate wake modulation, in collaboration with M. Vial. This setup aims at studying [he wake of
a fiat plate parallel lo the flow, and the modulation this flow by a smafl flap at the trailing edge of the
plate. A mechanic harmonical forcing of [he wake is obíained by performing tiny oscillations of the
flap with an externa] shaker. A schematic drawing of the experiment is given in Appendix A.3.
• Ultrasound scattering system, in collaboration with R. Frias. Associated with Proyecto
FONDECYT 1020134, the initial setup of ultrasound scattering technique was une of thc goals of [he
present project. My contribution in this area was mainly in [he design of the positioning systcm for
transductors, which has to be very accurae in order to have a good precision in vorticity
measurements. A picture of the general setup in shown in Appendix A.4.
• Vortex gun, in collaboration with G. Ruiz. A cylindric chamber is closed on OflC side by a loudspeaker, and on the other present a hole with specific shape. The Ioud speakers is driven with a
optimized signal [o generaLe a self propagating vortex, which shape is constrained by (he hole
(vortex ring for round hole, vortex dipole for long siot hole ... ) The atmosphere of [he chamber can be
adapted lo specific needs (smoke for visualization, inflamable gaz for combustion studies, etc.)
Appendix A.5 gives as an example the visualization of a vortex dipole at the exit of the generator.
3
1.2 Experiments and scientific results (Objective 2)
Large scale vortex fiow. The flow visualization technique, coupled [o velocity field measurements
and surface pressure readings on a Iarge cylinder in cross flow inside the wind tunnel, was used to
study a large scale vortex flow: it confirmed [he presence of a periodic shedding. An adaptalive
averaging technique allowed us lo compute the instantaneous pressure fluctuating fleid synchronized
to the associated vortex shedding cycle, thus enabling a coherent lift and drag computation. Flow
imaging allowed to record [he inner structure of [he fluctuating boundary layer at the separation
point, as well as the riear wake. 21) imaging correlation [echniques proved to be an efficient tool as
well to study Ihe periodic evolution of the wake. Appendix B.1 consist in the communication of these
results, published in [he Proceedings of me Décimo Congreso Chileno de Ingeniería Mecánica COCÍM 2002 - Santiago de Chile, 15-18 October 2002.
Driving (he wake of a fiat plate. A second set of experiments was dedicated to the wake of a fiat
plate parallel [o [he flow, and the possibility lo modulate this flow with a srnall flap at the Irailing
edge of the plate. At low Reynolds number, frequency response results display strong evidence of a
spatio-temporal resonance of the near wake even though the forcing amplitude is very small.
Arbitrary signais like discrete number of bursts and wave packets have been successfully propagated
through the fiat plate wake. lot wire mea.surements and flow imaging allowed to record [he inner
and outer structure of the forced wake and to map the flow resonances. Appendix B.2-4 consist of the
communication of these results:
> B.2 article submitted to Experiments influids.
B.3 article to be published in Instabilities and Non Equilibrium Structures IX, O Descalzi, J.
Martínez and S. Rica (Eds.) Kluwer Academic Publishers, pp. 195-206. In press (2003)
> B.4 communication in the Proceedings of me Décimo Congreso Chileno de ingeniería
Mecánica - COCIM 2002 - Santiago de Chile, 15-18 October 2002.
Wake coupllng, in collaboration with A. Prat and S. BuccicardL In sorne receni experimen[s we
studied the coupling between the wakes of three parallel cylinders in the wind tunnel, using a local
vortex shedding control technique [o synchronize the wakes. We generically observe a phase
opposition coupling between the Bénard Von Kármán vortex street of [he outer cylinders, leading lo
a constrained evolution of [he middle wake: depending on the Reynolds number. [he wake can be
laminar, consist in a unusual symmetric vortex street, or simply in the classic Bénard Von Kármán
pattern in phase with one of [he ou[er wakes. A unusual visualization technique ([he light plane being
perpendicular to the smoke plane) has been used and allows exp!onng the third dimension of this
supposed two dimensional tlow. Research in this area is still in progress and may end np in a
communication in a near future. Appendix B.5 gives as an example [he inhihition of the central
vor[ex street illustrated with classical hot wire anemometry.
Recent experiments. A few ideas have been rapidly tested recen[ly and may lead [o in[eresting
results if we find time to carry on in this direction. Among these, let us cite vortex ring collapse, in
collaboration with G. Ruiz (we shoot a vortex on a plane and study jIs disapparition with
pressure/sound ernission mea.surements and flow visualization), or bubble wake, in collabora[ion
with R. Hinrichsen: the rise of a bubble in a vertical Hele Shaw celi leaves a Bénard Von Kármán
vortex street in its wake, which by reaction deviate the bubble from its pure vertical ascension. The
study of the trajec[ory of [he bubble Ieads to its acceleration and [hus to [he drag and lift forces acting
on it. Appendix B.6 gives an example of the visualization of this vortex street with ink in the fluid as
a fiow tracer.
4
Part 2: Soft glassy materials
This research is an original work which begun with this postdoctoral project, without any preliminary
work in the area in the laboratory. The objective is Lo study experimentally the cross iníluence of aging
and flow in these intrinsically out of equilibrium materials (cg. gel in formation), using severa) forcing
methods: heat transport using a Rayleigh Bénard setup, simple shear fiow, and surface waves.
Afl ihe experiments were performed on Laponite preparations, a material considered has a generic
exampie of soft glassy systems.
2.1 Experimental realizations (objective 3)
An important part of my activity in the laboratory has been dedicated to thc design and realization of a
few experimental facilities:
Rayleigh Bénard convection setup. The convection ccii is rectangular: 145mm long, 68mm deep
and 23.5mm high. The lateral walis are made of iOmm thick Plexiglas, and top/bottom piaLes are
made of l6mm thick stainiess steel. Severa¡ platinum sensors (RTD-100) are placed in the two metal
piate bodies, ciose to the ccii surface, to mea.sure temperature gradient and uniformity. Al]
measurements are made with a Keithley 2000 multimeter and sean card in 4 wires configuration. The
cold plate temperature is controhied with a circulation from a water bath, aliowing better than 0.1K
temperature uniformity and stabihity. Thc other piale is heated with a 18W fiat sheet resistance of
rnatched size. This resistance is connected to a DC power suppIy (HP E3632A) in a 4 wires
configuration, which allows precise heating power setting. All instruments are remote controhied
with a computer via GPIB interface, which allows samphing temperature of the various sensors aL 0.1
Hz and controiling hot temperature with a PID algorithm: we achieve better than 0.5K temperature
uniformity and 0.03K stability. The temperature of the externa¡ environment is stabiiized Lo better
than 0.5K over 24h. To minimize heat exchange of the ccii with the environment, the hot and coid
plate temperature are set symmetricaliy to the room one, and both piates are imbedded in a tick
polystyrene isolation. In ihe worst case (conductive configuration), heat ioss represent only 30% of
total heating power. Eventuaily, the whole ccii can be precisely rotated along its short horizontal axis
with a computer controlled stepper motor (electronic controhier and programmation library are home
inade tools too), [o modify the orientation of the temperature gradient. A few views of the
experimental setup are given in Appendix C.1-3.
Pattern visualization. A original technique has been developed for pattern visuaiization: a
horizontal iaser iight sheet crosses the ccli along jIs shorter iength, 2mm aboye the bottom piate. It is
deviated by the temperature gradient inside the ccli. lIs projection on a sianted screen (to magnify
deviation) fohiow the temperature pattern, and can be recorded with a digital camera. Wc extract
from the raw image the position of the maximum intensity une. After appropriate rescaling, we even
llave quantitative access to the vertical temperature gradient along the ccii. A precise description of
this technique is given in Appendix D.1 (articie in preparation for The European Physical Journal 8)
Density measurements setup. The measurement of density and thermai expansion coefficient of
Laponite preparation was necessary to understand the aging properties of this material in convection.
A simple experiment was built, using a 175m] giass tank connected to a Smm diameter expansion
tube. The temperature of the tank is controiied with a thermal bath with better than 0.1K stabihity.
Precise weighting of the sampie when fiuiing the ccii ahlows density measurements (distihled water is
used for caiibration), and thermal expansion can be monitored by foilowing the hiquid leve¡ in the
expansion tube when changing the temperature. Precision is better than 0.3% in density and 5% in
thermai expansion coefficient.
5
Shearing system. This technique uses the microsized pores of syringe filters (Whaman Puradisc
25GD, 1pm) lo have a reproducible shear: the sampie are injected in the ccli through this membrane
using a controlled pressure difference (cg. with nitrogen at 2 bar). The tiny scale of this shearing
ailows a complete destruction of any preexistent gel structure in the preparation, and can be use both
for the initial measurement and (o reinitialize the sampie after aging. This method as been preferred
to another that was initiaily considered: a Taylor Couette flow. Not oniy this last techniquc had
aiready been dee.piy investigated by other groups - P. Coussot el al. Phys. Re y . Lett. 88, 175501
(2002) ; D. Bonn et al. Phys. Re y . Len. 89, 015701 (2002) ; V. Viasnoff et al. Cond-mat10210636
(2002) - but it does not aliow reaching such smaii spacial scales as the microshear method.
Eiectrical conductivity measurement. The study of a second observable during the convection
experiment, disconnected from the rheological properties of the sample, is useful to understand the
processes of aging Wc chose to made an electrical conductivity measurement, using the two metallic
plates as thc ciectrodes. Using a lock-in amplifier at high frequency, we get rid of the capacitive
interface contribution of the electrodes (Debye iayer), and follow adequately ihe evolution of (he
electrical properties of the sampie in time.
Faraday experiment. Eventualiy, we buiit a small Faraday ccli (o study the aging of surface waves
in Laponite. Thc ccli is circular with a diameter of 60mm, and a depth of 3rnm. A specific design
aliows top fiiiing of the cdl to the brim, to pin the meniscus outer position. The ccli can be sealed
with transparent film to avoid solvent evaporation or solution contamination by the atmosphere.
Vertical acceleration up to 20g is provided with a small electromagnetic shaker BK4810. A view of
this experimental setup is given in Appendix C.4.
2.2 Experiments and scientific results (Objective 4)
• Basic aging properties. To have a deep understanding of the convective behavior of Laponite
sampies, we first need to know how their basic properties are usualiy evolving, specifically those
entering the construction of the Rayleigh number: density, thermal expansion coefficient, thermal
conductivity, viscosity. The two first parameters were studicd using the density measurement setup
described before, and where found to be independent of time: no aging at ah can be observe on these
Iwo observables of the material. In fact, as could be guessed from (he sampie composition (more
than 97% of water), these properties are basicahiy those of water within a few percent. Likewise, (he
thermal conductivity of Laponite sampie is not distinguishabie of that of pure water: in a conductive
configuration of the Rayieigh Bénard ccli (heating from abo ye), we measure =0.6 Wm'K'.
Eventuahly, viscosity is the oniy aging parameter in the Rayieigh number: as measured with a Boihin
commerciai rheometer during my visit in France, it increases by more than 3 orders of magnitude
during thc gel formation. Thus, we expect the foliowing scenario for a simple convection experiment
(heating from below with constani temperature difference): first the sampie is rather liquid, and
convection is intense, then it is gradually slowing down toward a stationary conductive state, when
the viscosity of the sample reaches a critical value. These results are covered in detaiis in appendix
D.I (article in preparation for The European Physi cal Journal 8).
• Convection experiments. As inferred from the basic aging properties of Laponite sampies,
convection is indeed time dependent, evolving from a initial turbulent state toward a final conductive
state. Experiments were performed with severa] preparation concentration (ranging from 1.8 to
2.8wt%), uslng a 811 temperature difference between (he bottom hot plate and the top coid one, and
reproducibihity was tested with real ensemble averages (the same experiment reproduced several
times). The duration of convection was found to depend exponentially on concentration, froni 1 h for
the most concentrated sampies up to 15 days for the lowest concentration. This results is in striking
agreement with light scattering measurements performed by M. Kroon et al. - Phys. Re y. E. 54
p.6541 (1996). Dispersion in Nusselt curves for a single concentration were interpreted with the
pattern visualization: more rolis (thus more shearing) corresponds to a longer convection state.
indeed, the convective flow is changing (he aging behavior, as the pattern selected from an aleatory
initial condition (turbulent state) by the Rayleigh Bénard instability changes the time evolution of the
viscosity. This hypothesis has been partially confirmed by more complicated thermal protocols: if
the sample is kept with the sarne temperature difference in a conductive configuration (heating from
abo y e) for a long enough time, then switched to the potencialy unstable configuration (heating from
under), no convection at alt can be seen. Detailled description of these experiments and their
intcrpretations can be found ¡n appendix D./ (article in preparation for The European Phvsical
JournaiB).
Recent experiments. In a series of recent experiments, we focused on two complemcntary
measurements of these convection experiments: the use of a strong shear to reinitialize aging and a
parallel determination of thc electrical properties of the samples. The shearing method described
before can be used successfully lo partially rejuvenate a sample when convection is over: the ccli is
emptied and cleaned before another measurement, but the preparation is carefully kept. The
unavoidable loss of product during the cleaning operation is compensated with sorne reserve of the
initial preparation. The quite viscous sample is then injected again in the ccli, via (he microsized
porous filter. This treatment does reduce drastically the viscosity of the sample, as convection can be
seen again. Anyway, although any preexistent gel structures must be destroyed by this strong
shearing, the observed aging is not similar to the initial one: convection is initially less intense (the
initial Nusselt is half that of the first experiment) and shorter (about three times faster to rcach the
conductive state).
The behavior of the electrical resistivity of the sample during these processes is quite instructive:
during the initial aging, it decreases, in perfect agreement with other measurements performed with
the preparation at rest - L. Bellon et al. Europh y s. Le!!. 53, p.511 (2001). After reinitialization, the
electrical resistivity dccreases again, but starts from its value at (he end of previous experiment. The
filtering process induces a discontinuity in the viscous properties, as convection can occur again,
whereas the electrical properties are continuous in this process. This observation of differential aging
on two distinct observables in a single experiment is very instructive, and can be understand within
(he frarnework propose by T. Nicolai et al. Langmuir 16, p.8189 (2000).
The analysis of experimental data in these arcas is still in progress and may lead with cornplementary
experimenis to interesting results. An illustration of the effect of a reinitialization is given in
appendix D.2.
Conclu.sion
As commented in the previous lines, this post-doctoral project lcd to the creation of numerous
experimental facilities, including a complete and versatile Rayleigh Bénard convection setup. The
research activity was driven in parallel on Iwo different topic, dealing with vortex shedding and soft
glassy materials. The first subject, in continuity with the previous works of the laboratory, gaye
substantial resuits, leading Lo several publications (2 proceedings and 2 articles). The second activity,
being a new research area, took longer Lo produce its flrst results, in thc forrn of an article in final stage
of preparation. Moreover, the huge amount of experimental data gathered during this project is still
under analysis at the time of redaction of this final report. Wc believe that sorne other cornrnunications
could come out of these analysis, and will anyway provide the basis of a future collaboration between
our laboratories in France and Chile.
7
PRODUCTOS GENERADOS POR EL PROYECTO
En esta sección debe incluir todo documento o material cuyo contenido corresponda substancialmente a los
objetivos del proyecto que se informa y en los que se explicite el N° del proyecto FONDECYT. Aténgase a los
formatos que se incluyen para cada tipo de producto generado. Sólo adjunte copia de los documentos no
enviados previamente a FONDECYT.
1. Artículos en revistas científicas nacionales o extranjeras con Comité Editorial.
Título del Artículo
Autor(es)
1
Mechanical forcing of the wake of a fiat plate
M. Vial, L. Bellon and R. Hernández
Nombre Completo de la
Experiments in Fluids
Revista.
NO------ Pág.
Año:
Ref. bibliográfica
Estado de la publicación a. la D Publicada - O En Prensa - O Aceptada
0 Enviada
fuentes
Otras
financiamiento,sUas hay de Proyecto FONDECYT 1990571
Título del Articulo
Coupling between aging and convective motion in a colloidaJ glass
Autor(es)
L. Bellon, M. Gibert and R. Hernández Nombre Completo de la
Revista.
The European Physical Journal B
Ref. bibliográfica
Año:
Estado de la publicación a la
fecha. *
En etapa final de elaboración.
fuentes
Otras
financiamiento, si las hay
N°
1/
Pág.
de
• Marque con una "X" lo que corresponda. Para trabajos Aceptados/En Prensa/Enviados adjunte copia de carta de
aceptación o de envío.
8
2. Otras publicaciones/productos.
Título
Book titie: instabihties and Non Equilibrium Siructu res IX
Tipo de publicación o producto
0 Monografía
O Libro
Capitulo de Libro
Marque con una W lo que o Mapa
corresponda
[o Seminano/Taller/Curso
E] Informe Técnico
O Software
O Patente
O Exposición de Arte
Otro Especificar: Article titie: Resonani behavior of the wake of a fiat
piale: hot wire and sound scaliering measuremenis, pp. 195-206
This article was reviewed by independent referee board prior Lo
acceptation.
Autor(es)
-
R Hernández, M Vial, L BellonCBaudet
Editor(es) (Libros o Capítulos de O. Descalz i.. J. Martinez,
S. Rica
Libros)
Nombre de
Organización
la
Editorial/
Kluwer Academic Publishers
Ciudad: Dordrecht
País: The Netherlands
Lugar y Fecha de Publicación
Fecha: In Press
Titulo
Image acquisition software
Tipo de publicación o producto
O Monografía
O Libro
D Capitulo de Libro
lo que o Mapa
Marque con una
corresponda
O Patente
0 Exposición de Arte
Oro.echcar:
Autor(es)
JñSerninano/TaUer/Curso
O Informe Técnico
E21 Software
-
Ludovic Bellon
Editor(es) (Libros o Capítulos de
Libros)
Nombre
de
Organización
la
Editorial/ Depto. Ingeniena Mecanica, U. De Chile
País:
Lugar y Fecha de Publicación
1
Fecha:
3. Presentaciones a Congresos Nacionales e Internacionales. Adjunte copia del resumen o texto de la ponencia y de la tapa
del libro de Resúmenes, si no la ha enviado previamente.
Título de la Ponencia
Dináiiiica de vórtices de gran escala
Autor(es)
R.H. Hernández, L. Bellon
Nombre del Congreso Décimo Congreso Chileno de Ingeniería Mecánica - COCIM 2002 Lugar y Fecha
País: Chile
Ciudad: Santiago
fFecha: 15-18 octubre 2002
Título de la Ponencia - Modulación y propagación de ondas en la estela de una placa plana
Autor(es)
M. Vial, L. Bellon, R.H. Hernándci.
Nombre del Congreso Décimo Congreso Chileno de Ingeniería Mecánica - COCIM 2002 Lugar yFecha
País: Chile
Ciudad: Santiago
ID]
Fecha: 1518 octubre 2002
W. OTROS LOGROS DEL PROYECTO Describa, si las hay, actividades tales como:
Estadías de investigación
1 Cualquier otro logro no contemplado en los ítems anteriores y que Ud quiera destacar.
During these two years of posidoctoral position in Chile, ¡ had the opportuniiy [o meet a pan of jis
physician community and enjoyed [he fruitful discussions we had. 1 also had the opportuniiy lo preseni
my previous works in the 9th International Workshop on Instabilities and Non-Equilibrium Structures,
17-21 december 2001, Viña del Mar, and in a seminar in [he Departamento de Física de la Universidad
de Chile. The specific results of my postdoctoral project were re.cently presented in two seminars, one in
the Departamento de Ingeniería Mecanica de la U. De Chile, and another in the Lahoratoire de physique
de l'Ecole Normale Supérieure de Lyon.
Moreover, 1 had [he opportunity lo assist several students during their training period: Manuel Vial
and Rodrigo Frias (students of the Departamento de Ingeneria Mecanica, U. de Chile - mechanical
engineering thesis), Ricardo Hinrichsen (student of the Departamento de Ingeniería Mecanica, U. de
Chile - firsi doctoral year) and Mathieu Gibert (French student, form [he Ecole Normale Supérleure de
Lyon - master thesis in physics.)
Lasi bu[ not least, 1 would like to emphasize thai this postdoctoral project could be realized in a very
motivating environment and in excelleni experimental conditions. The skills, enthusiasm and
availability of Rodrigo Hernández, ihe high quality scientiíic equipment of the laboratory, coupled lo
the comfortable budget allowed by FONDECYT to conduct these experiments, are certainly the base of
the results produced by this projeci. This experience has been jugged very positive in France [00, whcrc
¡ have been ranked first for the perrnanent position 1 was applying for in the CNRS (Centre National de
Recherche Scientifique). ¡ hope my example will promote Chile as a convincing alternative lo the
LTnited SUite or Europa for a postdoctoral position, and that a future collaboration will allow us to keep
on exploring the prornising tracks we followed with this project.
V. INFORME DE EVALUACION DEL INVESTIGADOR PATROCINANTE
NOMBRE: Rodrigo Hernández
El Dr. Bellon realizó con éxito la totalidad de las actividades correspondientes a los dos primeros años de su
proyecto de post-doctorado, superando con creces las espectativas científicas planteadas en el proyectc
original. Recientemente, y en gran parte gracias al alto nivel científico de su trabajo en nuestro Laboratorio, e
Dr. Bellon fue seleccionado en el primer lugar para un puesto permanente en el CNRS, Centro Nacional de 1
Investigación Científica Francés, que tendría efecto el 1 de Octubre del 2003. A raíz de ello, él presenta un
arta de solicitud de fin anticipado al tercer año del proyecto de post-doctorado.
El producto de su trabajo científico queda resumido tanto en las publicaciones que se encuentran en anex
como en la gran cantidad de montajes y técnicas experimentales que él diseñó y construyó, y que ho
constituyen parte importante del patrimonio de nuestro Laboratorio.
Las publicaciones producto de su trabajo, pueden ser divididas en las distintas áreas asociadas a lo
objetivos originales del proyecto, considerando que el tema central es el Control de Sistemas Fuera de
Equilibrio.
-Flujos Abiertos y Métodos de Visualización: 1 trabajo publicado en acta de congreso (Anexo Bi. 2002).
-Control de Estelas y Generación de Paquetes de vórtices: 1 trabajo publicado en acta de congreso (134.
002), y 1 trabajo enviado a referato para la revista Expenments in Fluids (Anexo 132. 2003).
-Scattenng de ondas acústicas: 1 trabajo publicado (Anexo 133. 2003).
-Envelecimiento de Geis y Convección de Rayleiqh-Bénard: 1 trabajo en preparación para la revista
European Physical Joumel B (Anexo Dl .2003).
Quiero destacar otros logros producto de su proyecto de post-doctorado que a mi juicio son importantes:
-Dedicó gran parte de su tiempo, como co-guía, en la Tesis de Ingeniero del Sr. Manuel Vial, alumno de
nuestro laboratorio, lo que generó dos trabajos científicos para publicación.
El Dr. Bellon desarrolló íntegramente el software de adquisición de imágenes con que cuenta nuestro
Laboratorio en la actualidad, una herramienta imprescindible para la visualización y tratamiento de imágene
luidas y que reviste un ahorro sustancial de dinero frente a la compra de software comercial.
El experimento de ondas de Faraday fue construído íntegramente, y se encuentra en funcionamiento hoy e
nuestras dependencias con la posibilidad de estudiar fluidos complejos (gel, suspensiones coloidales,
polímeros) y además permite el estudio de sistemas granulares fuera del equilibrio.
-El trabajo del Dr. Bellon relativo al envejecimiento de gels como la Laponite, condujo al diseño
construcción de una célula de convección tridimensional, para el estudio de la inestabilidad de RayleighH
Bénard. Dicha célula posee control de temperatura de lazo cerrado incorporando un algoritmo P10. Es l
primera vez que se estudia este fenómeno en chile con este grado de precisión.
.En relación a este último tema, dedicó gran parte de su tiempo como guía de nuestro estudiante en estadía
de investigación, el Sr. Mathieu Gibert (alumno de física, maitrise de I'ENS Lyon) que finalizó con una tesis
publicada en francia de la cual guardamos celosamente una copia. El Sr. Mathieu Gibert obtuvo la calificaciór
más alta de su promoción con dicho trabajo experimental, que además generó una publicación.
La actividad originada por la presencia del Dr. Bellon en nuestro Laboratorio es, en mi opinión, digna de
reconocimiento. Por estos motivos, mi evaluación de su trabajo, es muy positiva.
Firma Investigador Patrocinante
Fecha:
12
VI. RESUMEN (NO DEBE EXCEDER ESTE ESPACIO)
Describa en forma precisa y breve el tópico general del proyecto, sus metas y objetivos y los resultados
alcanzados. Utilice un lenguaje adecuado para la comprensión del público no especialista en el tema.
En this experimental project, we explore sorne out of equilibrium systems and potential control methods of
their properties. The study focuses on two rather different classes of problems. -Me firsi part deals with
opens fiows, specifically on vortex shedding in the wake of a bluff body, whereas the second pali concerns
intrinsically out of equilibrium systems: glassy materials.
The mechanism of vortex shedding in the wake of a bluff body, although the phenomenon has been
observed for centuries, is still not fully understood. We use novel techniques of wake control to investigate
properties of these fiows and Eheir feedback on the obstacles. Thc cxperiments are performed by placing
different bluff bodies (cylinders or fiat plate) in a wind tunnel. The wake control is performed using
methods adapted to the obstacle, like pressure modulation at the surface of the cylinders lo inhibit vortcx
shedding, or harmonic forcing of a flap at the trailing edge of the fiat plate to probe its wake resonances.
The downstream velocity tields are measured by means of coherent average techniques OH classical hot-wire
anemornetry, and visualized with smoke panicules advection, while forces acting on ifie body are measured
with pressure sensors.
Our first results characterize the uncontrolled fiow and associated body forces on a turbulent large scale
vortex flow, leading to a better understanding of the relation between the periodic vortex shedding and the
dragflift fluctuations. Next, we performed a wide characterization of the wake of a fiat plate forced by a
small flap: probed by tiny oscillations at low Reynolds number, the frequency response results display
strong evidence of spatio-temporal resonances in the inner and outer structure of the forced wake.
The mapping of these resonances allowed Lo use this technique to propagate arbitrary signals like
discrete number of hursts and wave packets in the wake of the fiat plate. Likewise, we demonstrate
thai the wakes of three parallel cylinders can be synchronized using the pressure modulation
method, aliowing the creation of various vorticity distribution. These tools to generate known vorticity
fields present a first step for an exploration of the stability and interaction of these objects, aiming at giving
new leads on their role in turbulent fiows.
The second pali of this project deals with soft glassy materials, which are intrinsically out of equilibrium:
they present aging at rest, that is they never reach a Lhermodynamical equilibrium in a reasonable time and
any physical property of these systems will slowly evolve with Lime. According to a recent theoretical
approach, aging in these materials could be modified (controlled ?) by applying a constant externa¡ forcing.
We test those ideas on Laponite preparation, a canonical exaniple of these materials, using heat transport as
the forcing rnethod: in a Rayleigh Bénard convection set-up, heat transport act both as a tool Lo trigger fluid
motion and associated shear forcing, and a probe to measure the evolution of viscosity. The experimenis
follow the evolution of the convective tlow from the initial turbuleni state (a young sample has a low
viscosity) Lo a purely conductive state (when the increasing viscosity reaches the Rayleigh Bénard critica]
value), using temperature pattern visualization and heat transfer measurements. After a wide study of the
role of sample concentration, we demonstrate the interaction between flow properties and aging behavior
(eg. more convection rolis delay aging), in connection with cited theoretical approaches. These experiments
are completed with rejuvenation tests (using a microscopic scale shearing method) in parallel with electrical
properties measurements to probe ihe physical mechanisms responsable of aging. This study present a first
step toward controlling (stopping ?) the aging of glassy systems.
These two palis of the project, although quite disconnected from each other, both belong Lo the area of nonlinear physics, and are thus studied with similar tools. Moreover they aim aL a common goal: conLrolling (he'
effects of out of equilibriuni systems. They offcr both practica] and fundamental interests, ¿md lcd lo various
scientific communications.
13
INFORME 11NAI. CONCURSO FONDICYT - POSTDcX1ORADO - PROYECTO 30I067
Anexo A: Experimental realizations for vortex shedding studies
Fig. AA: Smoke injection system
Fig. A.2: Snapshot of home-made image acquisition software
14
INIORMI FINAL CONCURSO FONDECYT - POSTDOCTORADO - PROYECFO 3010(X7
Anexo A: Experimental realizations for vortex shedding studies Fig. A.3: Fiat piate wake moduiation setup
Fig. A.4: Ultrasound scattering system
15
INFORME FINAl, CONCURSO FONI)ECYT - POSTDOCFORADO - PROYFC10 3010067
Anexo A: Experimental realizations for vortex shedding studies
Fig. AS: Visualization of a vortex dipole at the exit of the voriex generator
[E
INFORME FINAl. CONCURSO FONI)ECYT POSTDOCTORADO - PROYECTO 3010067
Anexo B: Experimental results in vortex shedding studies
B.1 Attached communication:
Dinámica de vórtices de gran escala, R.H. Hernández, L. Bellon, cornmunication in Ehe Décimo
Congreso Chileno de Ingeniería Mecánica - COCJM 2002 - Santiago de Chile, 15-18 October 2002
B.2 Attached article:
Mechanica!forcing of ihe wake of a fiat piare, M. Vial, L. Bellon, R.H. Hernández, article subrnitted to
Experiments in fiuids (2003)
B.3 Attached anide:
Resonani behavior of ihe wake of a fiat piale: hot wire and sound scaltering nzeasureinefl!S,
R. Hernández, M. Vial, L. Bellon, Instabilities ant! Non Equiiibrium Síructures IX , O. Descalzi, t
Martínez and S. Rica (Eds.) Kluwer Acadcmic Publishcrs, pp. 195-206. In prcss (2003)
B.4 Attached communication:
Modulación y propagación de ondas en la estela de una placa plana, M. Vial, L. Bellon, R. Hernández,
communication in the Décimo Congreso Chileno de Ingeniería Mecánica - COCIM 2002 - Santiago de
Chile, 15-18 October 2002.
Fig.B.5: Inhibition of the central vortex street illustrated with classical hot wire anemometry
]so-velocity contours
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18Ç
1
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06
-
06
04
02
-30
-0
-10
0
probe posiIRJn v/t/
17
10
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NUORMEFINAL CONCURSO IONI)ICYF - POSIDOCIORADO - PROYECTO 30IO(7
Anexo B: Experimental results in vortex shedding studies Fig.B.6: Bubble rise in Hele Shaw ccli
• __
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INR)RMI lINAI (ON('IIRSO FONI)IT'YT POSIl)(X1ORADO - PROYECTO Oi(X7
Anexo C: Experimental realizations for soft glassy material studies Fig. C.1: Convection ceil
1
(isolation has been removed to show water circulation systein)
Fig. C.2: Convection ccli in measuring contiguration
Fig. C.3: Convection ceil with automated rotation system
1
LL/1\
lE
INI ORMI IINAI. CONCURSO FONDECYT - POSTDOCTORADO - PROYECTO 301(X7
Anexo C: Experimental realizations for soft glassy material studies Fig. C.4: Faraday ceH to study surface waves
r
Fig. C.5 : Measurement of surface modulation with laser plane deflection
20