• INFORME FINAL C.C3911K`MO 1.4 t HILE

FflNÜCVT PROYECTO FONDECYT POSTDOCTORADO

3010067 Inicial 3 años ¡ Final 2 años

NUMERO PROYECTO - DURACIÓN

Ludovic Bellon

INVESTIGADOR POSTOOCTORADO - -

Depto. Ingenieria Mecanica, U. De Chile, Bcaucheff 850, Santiago

DIRECCION

bludovic@cec.uchile.cl E-mail

14.740337-2

RUT

(2)6784617

FONO

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

)tros (especificar)

SERA ENVIADO (FECHA)

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 : bludovic@cec.uchile.cl

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 scientific cornrnunity in my research anca. Duiing this visil. 1 had very nich and enlighting 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.

Objetivos¿Cumplido? Fundamentación para el cun

incumplimiento Si Parcial No

1. Open fiows - design and implementation of: - Flow visualization technique - Wake control / vortex generation methods 0 O O - Ultrasound scatering technique

2. Open fiows - study of: - 2 wake control methods - Coupling vortex shedding / drag, Iift forces 0 O O - Generation of vortex wake packets

3. Soft glassy systems - design and realisation of: - Heat tranfer experiment - shcar experiment 0 O D

4. Soft glassy systems - study of: - Aging properties - lnstability behavior 0 O O - Coupling betwcen aging and flow

plimiento parcial o

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 loud-speaker, 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.

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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.

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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. Rey . Lett. 88, 175501

(2002) ; D. Bonn et al. Phys. Rey . 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 aboye), 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. Rey. 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 ye) 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 ys. 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.

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Autor(es)

M. Vial, L. Bellon and R. Hernández

Nombre Completo de la Revista. Experiments in Fluids

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 1 Mechanical forcing of the wake of a fiat plate

Ref. bibliográfica Año: NO------ Pág.

Estado de la publicación a. la D Publicada - O En Prensa - O Aceptada

Otras fuentes financiamiento,sUas hay de Proyecto FONDECYT 1990571

0 Enviada

Título del Articulo

Autor(es)

Nombre Completo de la Revista.

Coupling between aging and convective motion in a colloidaJ glass

L. Bellon, M. Gibert and R. Hernández 1/

The European Physical Journal B

Pág. Ref. bibliográfica Año: N°

Estado de la publicación a la fecha. * En etapa final de elaboración.

Otras fuentes de financiamiento, si las hay

• Marque con una "X" lo que corresponda. Para trabajos Aceptados/En Prensa/Enviados adjunte copia de carta de aceptación o de envío.

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2. Otras publicaciones/productos.

Título Book titie: instabihties and Non Equilibrium Siructu res IX

0 Monografía [o Seminano/Taller/Curso Tipo de publicación o producto O Libro E] Informe Técnico

Capitulo de Libro O Software Marque con una W lo que o Mapa O Patente corresponda 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 - Libros) O. Descalz

.i. J. Martinez, S. Rica

Nombre de la Editorial/ Organización Kluwer Academic Publishers

País: The Netherlands Ciudad: Dordrecht

Lugar y Fecha de PublicaciónFecha: In Press

Titulo Image acquisition software

O Monografía JñSerninano/TaUer/Curso Tipo de publicación o producto O Libro O Informe Técnico

D Capitulo de Libro E21 Software Marque con una lo que o Mapa O Patente corresponda 0 Exposición de Arte

Oro.echcar: -

Autor(es) Ludovic Bellon

Editor(es) (Libros o Capítulos de Libros)

Nombre de la Editorial/ Organización Depto. Ingeniena Mecanica, U. De Chile

País:

Lugar y Fecha de Publicación1 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 Fecha: 1518 octubre 2002

ID]

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:

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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 non-linear 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.

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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

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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

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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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1-

06 -

06

04

02

-30 -0 -10 0 10 20 probe posiIRJn v/t/

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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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1 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 (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

LL/1\ 1lE

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

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