Communications during scientific events, Seminars,...

 

Top of the page

In 2024

Empreinte environnementale et soutenabilité des activités de recherche
Paris 5-7 Nov (2024)

• Projet d’expérimentation d’une recherche plus sobre et plus ambitieuse  presented by   ...

Les crises climatiques, énergétiques et écologiques actuelles imposent des changements de la pratique de la recherche dans les années à venir et des engagements à la hauteur des enjeux [1]. Au CNRS et plus particulièrement à l'Institut Néel (CNRS, Grenoble, Physique de la matière condensée, 450 personnes), 75% de notre bilan carbone est lié aux achats. Réduire significativement l’impact environnemental de notre recherche implique donc une diminution substantielle de ces achats. Peut-on accroître l'ambition de notre recherche tout en réduisant drastiquement nos achats ? Nous sommes convaincus que des marges de manœuvre peuvent apparaître en réduisant la fragmentation de nos financements par appels à projets (AAP). La systématisation des financements de la recherche fondamentale par AAP incite à l'achat de nouveaux équipements sans concertation à l’intérieur du laboratoire et entraîne du gaspillage dû aux achats contraints par le calendrier. Elle est également inefficace humainement (temps passé à rédiger, évaluer et gérer les projets, avec des taux de succès souvent trop faibles, lourdeur du suivi administratif,…) et scientifiquement (incitation à proposer de nouveaux sujets plutôt que de prolonger des recherches en cours, rigidité excessive, effets de mode, prise de risque limitée,…). Nous proposons d’expérimenter un mode de fonctionnement plus sobre, dont le fil directeur est une réduction volontaire de nos achats de 10% par an, soit une diminution de 41% en 5 ans. Ce projet serait possible grâce à un financement forfaitaire unique, nous libérant des contraintes actuelles liées à la fragmentation des financements. Cette nouvelle organisation permettrait de libérer du "temps de cerveau" pour mener une recherche de meilleure qualité avec un moindre impact environnemental, et d’expérimenter des modes de fonctionnement plus collaboratifs et mutualisés dans les décisions d’achat et les activités de recherche. Cette expérimentation sera menée par un collectif de quelques dizaines de permanents au sein de notre laboratoire sur une période de 5 ans, renouvelable. Les participants et participantes s’engageront à ne plus demander de contrats et recevront, en contrepartie, une somme forfaitaire de la part d’un organisme financeur, à identifier, calculée sur la base des crédits reçus au cours des 5 dernières années, avec une réduction annuelle de 10 % sur la partie dédiée aux achats. Les modalités concrètes de ce fonctionnement (gouvernance, gestion financière, cohabitation avec le reste du laboratoire) seront définies lors d’un atelier de 2 jours, prévu pour la fin septembre, reposant sur des techniques d’intelligence collective [2], soutenu par le laboratoire et le CNRS [3]. Nous souhaiterions également que cette expérimentation soit observée et analysée par des chercheurs en sciences humaines et sociales (anthropologie, sociologie des sciences, des organisations, etc…) afin qu'ils nous aident à définir les critères d’évaluation en matière de qualité de la science produite, d’impact environnemental, de gouvernance et de bien-être des participants. Lors de cette contribution, nous présenterons le projet en détail et exposerons les principales idées émergées lors de l’atelier de septembre.

 

1st European Fluid Dynamics Conference (EFDC1)
Aachen 16-20 Sept (2024)

• Quantum turbulence : an energy-consistent closure for the HVBK equations  presented by   P.-E. R.

Below its superfluid transition, helium is described as an intimate mixture of two interacting fluids known as the superfluid and the normal fluid. The superfluid consists in a tangle of quantized vortices with atomic-scale diameters, whereas the normal fluid is a classical viscous fluid. The interaction between both fluids is mediated by vortices. The HVBK equations describe the superfluid at a coarse-grained scale, reducing it to a simple Euler equation. Unfortunately, this procedure eliminates information about the density of vortices at subgrain scales, which is necessary to evaluate the inter-fluid coupling. We propose an energy-consistent phenomenological model for the dynamics of vortices at subgrain scales, which allows to close the HVBK system of equation without adjustable parameters. The result is a set of three equations accounting for the dynamics of turbulent helium in its superfluid state. Numerical simulations are presented and compared with the state-of-the-art numerics of the HVBK equations done with alternative closures.

-> impossibilité de dernières minutes d'honorer cette présentation.

 

In 2023

9th International Conference on Rayleigh-Bénard Turbulence
Xi’an 16-20 Oct (2023)

• Ultimate Regime And Turbulent Transitions In Rayleigh-Bénard Convection  presented by   J. Salort (invited talk)

Turbulent Rayleigh-Bénard convection involves phenomena at various length scales: thermal plumes arise from buoyancy instable boundary layers, and their interactions yield a large scale flow which itself shears the boundary layers and produces a turbulent bulk. For higher thermal forcings, the boundary layers are expected to further destabilize, and the flow may become fully turbulent. Laboratory experiments in Grenoble were the first to evidence such a transition to a regime of higher heat-transfer, sometimes referred to as “the ultime regime” of convection. Yet, published experimental results show apparent contradictions. The transition to the ultimate regime has been reproduced in several Grenoble convection cells, in experimental conditions satisfying extremely strict Boussinesq conditions. In particular, the ultimate state is observed even when the key properties of the fluid (density, thermal expansion, conductivity, viscosity, heat capacity) are bound to stay within a 1 % window of variation, as reported in [5]. Other convection cell show no heat transfer enhancement [4], or only in Non-Boussinesq condi- tions [6], or at much larger Rayleigh numbers [2]. This raises the question whether Non-Boussinesq effects in these cells might hinder the transition, and cause the transition to the ultimate state to be differed or damped. To explore this possibility, we present unpublished heat transfer measurements obtained in Non-Boussinesq conditions, and show the impact of these deviations on the strength of the transition. The alternative approach in Lyon consists in going beyond this apparent contradiction by focusing on the characterization of the turbulent bulk: to that end, we use visualization methods such as shadow- graph and Lagrangian tracking of tracer particles. We add roughness to the plate to promote plume emission and boundary layer destabilization [1], and use several working fluids to explore the param- eter range: deiozied water, fluorocarbon and low temperature liquid helium. Our latest results suggest that the Nu-Ra relationship may not be the best method to pinpoint the turbulent transition, and that the threshold may be in terms of a Reynolds number rather than Rayleigh number, and highlights also the role of the Prandtl number on the threshold to turbulence [3]. This could, in part, lift the apparent contradictions reported in the literature.

 

Ecole thématique Instrumentation Cryogénique, AFF Pont-à-Mousson, Oct 9-12 (2023)

• Mesure de pression en contexte cryogénique. Etude de 4 cas pratiques  given by   P.-E. Roche

Le cours présente différents cas concrets de mesure de pression en milieu cryogénique. Le premier cas est la mesure de pression d’un vide cryogénique. Le deuxième cas est la mesure de pression d’un bain pompé. Puis le choix d’un capteur de pression à froid est exposé entre les transducteurs capacitifs, les transducteurs à réluctance variable et les transducteurs piézoélectriques.

 

Journée thématique de l'IMFT "Hydrodynamique quantique : les superfluides du macro au nano"
Toulouse, Sept 22 (2023)

• Des grandes échelles aux méso-échelles de la turbulence superfluide : Modèle HVBK et Instrumentation miniaturisée  presented by   P.-E. Roche

 

18th European Turbulence Conference
Valencia 4-8 Sept (2023)

• Spectrum and histogram of vorticity in a superfluid grid experiment  presented by   P.-E. Roche

A turbulent superfluid can be viewed as a dense tangle of vortex lines wiggling around. Strikingly, the collective behaviour of this tangle mimics classical turbulence at inertial scales, at least according to existing velocity measurements. This allows to envision superfluids as model fluids to explore the inertial-range properties of classical turbulence, in particular those difficult to resolve with classical fluids such as vorticity and enstrophy. Along this line, we report times series of the vorticity measured in a grid experiment (at 10M) using superfluid 4He at 1.65 K. The measurements are made with specially-designed micro-fabricated probes that are able to resolve the velocity and the density of vortex line at a scale around one millimeter. These probes are based on an open second-sound cavity forced at resonance (see photo). As expected, the velocity histogram is quasi-gaussian and the velocity spectrum evidences a scaling behaviour along more than one decade of inertial range, slightly less steep than -5/3 due to proximity to the grid (see plot). In contrast, the vorticity time series are strongly skewed -as expected- and the vorticity spectrum doesn't evidence any scaling range. Implications are discussed.

• Transition to the Ultimate Regime in Boussinesq and Non- Boussinesq conditions  presented by   J. Salort

Thermal convection at very high Rayleigh numbers remains elusive, as published experimental results show apparent contradictions. The transition to the ultimate regime has been reported in several Grenoble convection cells, in experimental conditions satisfying extremely strict Boussinesq conditions. In particular, the ultimate state is observed even when the key properties of the fluid (density, thermal expansion, conductivity, viscosity, heat capacity) are bound to stay within a 1 % window of variation, as reported by Roche et al. The transition to the ultimate regime is evidenced in gaseous and supercritical cryogenic Helium in Grenoble beyond a Rayleigh number within 1e11 — 1e13, depending on the cell aspect ratio . Other convection cell show no heat transfer enhancement, or only in Non-Boussinesq conditions , or at much larger Rayleigh numbers . This raises the question whether Non-Boussinesq effects in these cells might hinder the transition, and cause the tran- sition to the ultimate state to be differed or damped. To explore this possibility, we present unpublished heat transfer measurements obtained in Non-Boussinesq conditions, and show the impact of these deviations on the strength of the transition.

 

Bridging Classical and Quantum Turbulence
Cargèse, July 3-15 (2023)

• event co-organisation

• Estimer son empreinte carbone. Pourquoi ? Comment ?  Conférence grand public de   P.-E. Roche

Plongez dans l’univers de l’empreinte carbone ! Depuis près d’une décennie, les transporteurs aériens, maritimes et ferroviaires affichent l’impact carbone de chaque voyage. Mais que signifient réellement ces chiffres ? Quel lien avec le changement climatique ? Et surtout, comment ces déplacements se comparent-ils à nos autres activités en termes d’empreinte carbone ? Rejoignez-nous pour une conférence-découverte qui vous apportera un éclairage pédagogique sur ces questions cruciales pour le futur de l’humanité.

 

• Listening to quantum turbulence with second sound tweezers  presented by   P.-E. Roche

• On the role of mutual friction in He-II Turbulence  presented by   E. Lévêque

 

EGU General Assembly 2023
Vienna 23-28 April (2023)

• Traveling for academic research : patterns, determinants and mitigation options  presented by   O. Aumont

In the midst of climate change, academic travels - one salient aspect of the carbon footprint of research activities - are at the center of a growing concern. Mitigation options often focus on two dimensions : (i) decreasing the frequency of attendance to conferences and (ii) modal shift in transport. Here, we analyze professional travel in academia from a unique database compiling about 100 000 travels from about 150 research labs across a large array of disciplines and localities in France to detail the structure, patterns and heterogeneity of national and international research travels for research purposes. We estimate the mitigation potential of a series of options encompassing but not limited to institutional options. We show that, if short distance traveling (typically below 1000 km) are largely dominant in number, their relative mitigation potential via modal shift is small (i.e., below 15%). On the other hand, long distance traveling, which is often associated with international collaborations or field work hold a much larger mitigation potential but question the very nature of research activities. We propose ambitious sobriety options to robustly decrease travel-induced GHG emissions in academia and discuss their acceptability in the context of the French public research system.

 

 

In 2022

18th Journées de la Matière Condensée Mini-colloque: Superfluidity, vortices and quantum turbulence in atomic systems
Lyon, August 22-26 (2022)

• Mesophysics of quantum turbulence: the superfluid 4He route  presented by   P.-E. Roche (invited talk)

In 1940, Kolmogorov laid the foundations for the theory of turbulence in viscous fluids. In particular, he showed that the kinetic energy cascades in Fourier space from large to small scales, where it dissipates by viscosity. Strikingly, classical turbulence models account well for the turbulence of quantum fluids, at least at scale much larger than quantum scales [1]. What happens at smaller scales has been actively investigated over the last years, but locating and exploring the cross-over between large seemingly-classical scales and quantum scales raise practical difficulties. One difficulty of numerical and experimental studies is to generate a quantum flow with a wide separation between its classical and quantum characteristic scales (see figure and [2]). Another difficulty to develop a dedicated instrumentation that is able to resolve those mesoscales of quantum turbulence (e.g. [3,4]). This talk will spot grey areas of present understanding and draw on recent literature to illustrate the special role of superfluid 4He experiments, in particular those producing ultra-intense quantum turbulence and thus very large separation of scales.

 

Oberbeck - Boussinesq hypothesis and beyond in stratified turbulence Euromech colloquium 619
Vienna, July 4-8 (2022)

• Transition to the ultimate regime in Boussinesq and non-Boussinesq conditions  presented by   J. Salort

Thermal convection at very high Rayleigh numbers remains elusive, as published experimental results show apparent contradictions. The transition to the ultimate regime has been reported in several Grenoble convection cells, in experimental conditions satisfying extremely strict Boussinesq conditions. In particular, the ultimate state is observed even when the key properties of the fluid (density, thermal expansion, conductivity, viscosity, heat capacity) are bound to stay within a 1 % window of variation, as reported in [7]. The transition to the ultimate regime is evidenced in gaseous and supercritical cryogenic Helium in Grenoble [1, 7] beyond a Rayleigh number within 1011 — 1013, depending on the cell aspect ratio [6]. Similar transition was reported by Niemela and Sreenivasan [4], but the Boussinesq conditions are not as stringent as the one mentioned above [5]. Other convection cell show no heat transfer enhancement [3], or only in Non-Boussinesq conditions [8], or at much larger Rayleigh numbers [2]. This raises the question whether Non-Boussinesq effects in these cells might hinder the transition, and cause the transition to the ultimate state to be differed or damped. To explore this possibility, we present unpublished heat transfer measurements obtained in Non-Boussinesq conditions, and show the impact of these deviations on the strength of the transition.

 

Archipel 2022 Risques systémiques, trajectoires et leviers d’action transdisciplinaires
St Martin d'Hères, June 20-23 (2022)

• no communication

 

In 2021

seminar series "Experimental Physics and modelling
ENS Lyon, June 22 (2021)

• Second sound tweezers listening to quantum turbulence  presented by   E. Woillez

Superfluidity allows for propagation of temperature waves called « second sound ». This property has opened the rare opportunity to measure directly the presence of quantum vortices in a turbulent flow. During the last twenty years, a new generation of sensors, the « second sound tweezers » were developed at the Institut Néel. They allow to directly probe the small scale velocity and quantum enstrophy in the core of the flow. I will first recall the general characteristics of quantum turbulence, and some research perspectives in the field of quantum hydrodynamics. Then I will present in details the principle of second sound tweezers, and last, I will show some recent experimental results.

 

iTi 2021 interdisciplinary Turbulence initiative
Bertinoro, Feb 25-26th (2021)

• Second-sound tweezers: a new way to measure joint vorticity-velocity fluctuations  presented by   E. Woillez

Below a critical temperature Tλ ≈ 2,18K, liquid helium undergoes a phase transition to a superfluid state, with strongly temperature-dependent hydrodynamics properties. In the zero temperature limit, this liquid has zero viscosity, while it is expected to behave like a standard Navier-Stokes fluid right below Tλ. This remarkable property has prompted a number of both theoretical and numerical studies about turbulence in superfluid helium, to see in which extent it differs from its classical counterpart, but predicting the properties of superfluid turbulence when temperature is decreased is still an open question. One of the major challenge is to understand how those kind of turbulent flows can dissipate energy at small scale when viscosity vanishes. To answer this question, our aim is to resolve at the smallest possible scale the fluctuating fields of superfluid turbulence. Using particular micro-fabricated tweezers [1], we show that we are able to access jointly the local vorticity and velocity fluctuations of a grid turbulent wake. The small size of the probe compared to the grid size gives access to a wide part of the inertial scales [2]. The experimental setup is displayed on the left of figure 1. We create a stationary resonant temperature wave (second-sound wave) inside the tweezers, as displayed on the right of figure 1. When the turbulent flow crosses the probe, the vorticity is responsible for a bulk damping of the wave, without phase shift. By contrast, the velocity is responsible for a deflection of the wave, and creates both a phase shift and a damping. With a careful design of the tweezers plates, we are able to isolate the two component of the signal and capture both velocity and vorticity fields at the same time.

 

In 2019

17th European Turbulence Conference
Turin 3-6 Sept (2019)

• The Ultimate state of convection without the hot air  presented by   P.-E. Roche

Over the last 2 decades, the ultimate state (or ultimate regime) has become the most debated topic in the field of convection. More than a dozen of Rayleigh-Bénard experiments conducted at very large Rayleigh numbers (Ra) are often presented as in contradiction, due to diverging heat transfer efficiencies (Nusselt number Nu), as illustrated by the figure. Some experiments experience a more or less pronounced heat transfer enhancement at large Ra while others don’t. Over the years, three different views have emerged in Grenoble/Lyon, Brno/Prague/Trieste and Gottingen/Twente/Santa Barbara to account for the results. These views are based on variants of Kraichnan’s 1962 prediction of a fully-turbulent asymptotic state of convection, or on Boussinesq approximation effects. Taken separately, the respective datasets and/or model are certainly fair and self-consistent, but no proposed interpretation is yet able to account for all existing observations. We conducted a meta-analysis of all the experiments performed at very high Ra assuming that (1) all data are correct (2) the various biases that inevitably alter measurements cannot fully account for the onset of scatter right above Ra ~ 10^{12} (knowing that all data agree over decades of lower Ra). Among all the experiments reporting a strong heat transfer enhancement, we identify few robust signatures for the ultimate state (dependence with the cell aspect ratio, scaling exponent, etc …) and the conditions for its occurrence. Based on these observations, a focused exploration of the other datasets allows to spot weak signs of transitions, and in one case where a finite size artefact can explain the absence of such sign. We argue that most very-high-Rayleigh numbers experiments could be described in a unified fashion, stating that a transition to the ultimate state takes place but that a mechanism can damp the increase of heat transfer. Although a first model emerges for this mechanism, it is yet to be understood in details.

 

Workshop on different states of turbulence and transitions from one state to the other: small and large-scale aspects and their interrelations
Grenoble, Feb 13-14 (2019)
• Detection of different states of turbulence at very high Ra 

Over the last 2 decades, the “ultimate state” has become the most debated topic in the field of turbulent convection. More than a dozen of Rayleigh-Bénard experiments conducted at very large Rayleigh numbers produce apparently cont- radictory results, with diverging heat transfer efficiencies. The nature of the transition is vividly debated in the community, as well as the condition for its occurrence. We will present a meta-analysis of all experimental data and present evidence that all experiments could have entered the ultimate regime, but some in a damped “silent mode”, calling for new exploration tools.

 

Top of the page

In 2018

Séminaire du Département Science de la Matière
ENS-Lyon, Oct 17 (2018)
• Turbulence Quantique : la rencontre mouvementée de la mécanique quantique et de la mécanique des fluides 

Comment évolue un rond de fumée dont la vorticité est quantifiée ? Grâce à une telle expérience de pensée, Richard Feynman prédit en 1955 l’existence d’écoulements sans équivalent en physique classique, et désormais appelés « turbulence quantique » ou « turbulence superfluide ». L’adjectif « superfluide » renvoie à une phase exotique de l’hélium liquide permettant une réalisation expérimentale en dessous de 2,18 K. 60 ans plus tard, la turbulence quantique recèle toujours de nombreux mystères. Par exemple, on ne sait ni prédire ses conditions d’apparition, ni identifier le mécanisme physique expliquant sa dissipation dans les modèles expérimentaux. Mais le développement d’une nouvelle génération d’expériences, de simulations numériques et de modèles théoriques a récemment permis des progrès significatifs. L’exposé présentera quelques questions fondamentales ouvertes, et identifiera les défis expérimentaux, numériques, et analytiques a relever.

 

Journée Maths-Physique Superfluides et Supraconducteurs (affiche)
Lab. de Mathematiques Raphael Salem, Rouen, Oct 11 (2018)
• Fluctuations de la densité de vortex : enjeux et mesure expérimentale 

 

iTi Conference on Turbulence VIII
Bertinoro, Sept 5-7 (2018)
• Ultra high-resolution anemometer for turbulence: the Hanging Micro-hOt-Films (HMOF)  (Invited talk)

Handmade hot wire anemometers are the reference probes to explore the statistics of turbulence, thanks to their good space and time resolutions, and decades of design optimization. However, they fall short to resolve the smallest scales in flows at high Reynolds numbers (Re). Clean room tools allow to produce fully microfabricated hot-wires, resulting in one order of magnitude gain in resolution (typ. 50 µm). However, this improvement is not sufficient at the highest Re and additional miniaturization is highly difficult due to the resulting wire fragility. We propose a new approach in micro-machined thermal anemometry to gain two orders of magnitude in resolution over traditional hot wires. No sacrifices are made on the aerodynamic disturbances and thermal end-effects of the supporting structure, as these parasitic effects are known to alter the sensors dynamical response in complex ways at frequencies lower than the probe’s main cut-off frequency. The sensor consists in a web-like structure, with as many as 20 sensitive spots arbitrarily positioned across it, and independently connected. Each sensitive spot is a miniaturized platinum hot film, of typical size 3 µm × 3 µm, deposited on a 0.5-µm-thick and 1 mm-long ribbon of low thermal conductivity. If needed, the fabrication process allows further miniaturization. We will present operation of one of these HMOF (Hanging Micro hOt Film) sensors at very large Reynolds number (Rλ ~ 1570 - 3340) in the GReC jet [1]. Multiple sensitive spots were monitored simultaneously at a mutual relative distance of few Taylor microscales lengths, transversely to the flow direction. The power spectra below illustrate the wide-dynamics range of the resolved turbulent signal compared to other reference datasets from the literature.

 

Chasing tornadoes: vorticity above, below, and in the lab
Newcastle, April 9-11 (2018)
• Intermittency of turbulent He-II with superfluid fractions from 0% to 96%  

Puzzled by few numerical predictions in apparent contradiction, we perform a systematic experimental investigation of intermittency in He-II. The TOUPIE wind-tunnel is used, and the superfluid fraction is varied between 0% (He-I) up to 96% (He-II at 1.28 K). Velocity fluctuations are measured using a micro-machined cantilever anemometer positioned in far wake of the disc. Within accuracy, inertial-range intermittency was found independent of the superfluid fraction.

 

CMD27 : 2018 Joint Conference of the Condensed Matter Divisions of the EPS and the DPG
Berlin, March 11–16 (2018)
• Experimental exploration of intense quantum turbulence with He-II  (invited talk)

The exotic properties of quantum fluids open numerous opportunities to test our understanding of classical turbulence, for example on the role of dissipation and vorticity. However, each type of quantum fluids pose specific experimental challenges when it comes to generate and probe its turbulence. One quantum fluid, superfluid 4He (He-II) has favourable properties that allows to generated very intense quantum turbulence in classical wind-tunnels and stirring cells. In such conditions, a one-to-one direct comparison between classical and quantum turbulence becomes possible. We will present the recent progresses (and stumbling blocks) along this route. ( Mini Colloquium/Focus Session "Quantum turbulence and imaging of quantum flow of superfluids )

Top of the page

In 2017

 

Turbulent cascades II Euromech-Ercoftac colloquium 589
Lyon, Dec 5-7 (2017)
• Turbulent cascade in Superfluids  presented by E. Lévêque

 

School of Mathematics, Statistics and Physics, Newcastle University (seminar)
Newcastle, Oct 27th (2017)
• Hurricane hazard in a tangle of quantum vortices : screening intermittent events in a superluid turbulence experiment  presented by   P.-E. R.

 

Compressible Convection Conference 2017 CCC2017
Lyon 18-22 Sept (2017)
• Micro-fabricated in-flow sensors for convection : heat-flux probe and 3D temperature-gradient probe  presented by   P.-E. R.

Over the last two decades, micro and nano-fabrication equipments have become more and more widespread in the academic environment. They allow to develop highly-specific sensors, that would have been very delicate and time-consuming to manufacture with classical techniques. The talk will present two probes recently developed to study forced and natural convection in non-conductive fluids, across a broad temperature range [-200 °C +100°C]. The heat flux probe consists in a joint temperature-velocity probe, with a spatial resolution of a few hundred of microns. A deflecting cantilever is used to detect the signed velocity, while a platinum thin film thermometer provides the temperature fluctuations. The temperature-gradient probe consists in a multi-points Pt thermometer capturing simultaneously the temperature at the 8 corners of a millimetre-size cube. If the thermal « plumes » in the fluids are larger than 1-mm, the local temperature gradient can be extracted, and thus the thermal dissipation rate. If the plumes are smaller, their 3D space-time correlation can be reconstructed. Preliminary measurements will be shown.

 

Workshop on Fluctuations, Large deviations in Turbulence
Autrans 28-30 August (2017)

 

16th European Turbulence Conference
Stockholm 21-24 August (2017)

• Array of ultra-miniaturized hot-films for high Reynolds number flows  presented by   P.-E. Roche (work done with B. Chabaud, Olivier Pirotte, E. Rusaouen and J. Valentin)

Ultra-high-resolution (<10 microns) anemometers has been micro-fabricated for simultaneous measurements at different locations transversely to a flow. Each sensitive spot consists in a platinum resistance deposited within a 4 microns x 4 microns area in the center of a 4 microns-wide, 0.5 microns-thick and 1 mm-long ribbon. Up to twenty active micro-ribbons can be suspended across the openings of a grid made of 50-microns-cross-section rods. The whole structure, including the 12 mm x 12 mm outer frame and its support, meets the empirical X10 rule of flow invasiveness : any structure of size L is at least 10 X L away from the central sensitive spot. A prototype probe was successfully operated in the GReC jet experiment, from Reynolds numbers R_lambda ~ 1570 up to ~3340. Two micro hot-films, 1.4-mm away in the transverse direction to the flow, were simultaneously operated near the jet axis using CCA electronics. The 1.4-mm spatial separation corresponds typically to 1 or 2 Taylor scale lengths (depending on R_lambda). Spectral and cross-correlation analysis from the two signals will be presented. The power spectra below illustrate the wide-dynamics range of the resolved turbulent signal. The second figure is the coherence function of the two nearby `hot-spots'', which is the normalized cross-spectrum of the two signals at R_lambda~3340. The ~3 decades inertial-range (visible in the first figure) complemented by the high resolution of the sensor enable to observe a transverse decoherence of turbulence fluctuations fully imbedded in the inertial range.

 

Workshop on Measurement Methods in Turbulence
Grenoble 5-7 July (2017)

• Array of hot-spots for very high Reynolds number anemometry  presented by   P.-E. R.
• Cantilevers for cryogenic liquid Helium  presented by   J. Salort

 

New Challenges in Wall Turbulence
Lille 14-16 June (2017)

• Array of ultra-miniature hot-films for very high Reynolds number flows  presented by   P.-E. Roche

A new geometry of micro-machined anemometers is introduced for very high-resolution and simultaneous measurements at different locations within a flow. It consists in a web-like structure, highly transparent for the flow, with built-in sensitive spots arbitrarily positioned to probe correlations, gradients, mixed velocity/temperature signals, etc.... Each sensitive spot consists in an ultra-miniaturized Pt hot film, of typical size 5 micron X 5 micron, suspended on a submicron-thick mm-long ribbon. The specific geometry of the first fabricated prototype was on a regular grid with a 1-mm mesh size and 30-micron-thick rods. Each ribbon was positioned across an opening of the grid. Special care was dedicated to meet the empirical X10 rule of flow invasiveness: any structure of width (or thickness) L is at least 10XL away from the sensitive spots. See picture below. This first probe was successfully operated in the GReC jet, from Reynolds numbers R_{\lambda} ~ 1570 up to R_{\lambda} ~ 3340. Two micro hot-films were simultaneously operated near the jet axis using CCA electronics. Their spatial separation is 1.4-mm in the direction transverse to the flow. Depending on R_\lambda, it corresponds typically to 1-2 Taylor microscale lengths. The power spectra below illustrate the wide-dynamics range of the resolved turbulent signal.

 

Workshop ``Turbulence et polaritons"
Grenoble 7 June (2017)

• Experimental investigations of intermittent signatures in superfluid turbulence  presented by   P.-E. Roche

...

 

Quantum Turbulence Workshop
Tallahassee April 10-12th (2017)

• Observation of vortex bundles in highly turbulent He II  presented by   P.-E. Roche (work done with E. Rusaouen and B. Rousset)

We carried a systematic search and investigation of coherent structures in highly turbulent He-II. Measurements were carried for superfluid faction of 0%, 19% and 80%. The specificities of the SHREK experiment were used to generated ultra high Reynolds numbers, exceeding Re= 5.5 × 107 in a Von Karman configuration, and to track vortices. We found evidence for coherent superfluid vortex bundles. Their mean density, strength, spectral and spatial distribution are compared to those of vorticity filaments in classical turbulence.

Top of the page

In 2016

 

Séminaire Néel
Grenoble Dec 16th (2017)

• Phénomènes intermittents en Turbulence quantique et classique  presented by   P.-E. Roche

En 1941, le mathématicien russe Andreï Kolmogorov propose une théorie concise et élégante des fluctuations en turbulence. Cette théorie suppose que les tourbillons d’un écoulement se désagrègent continûment en des tourbillons plus petits, l’énergie cinétique étant conservée durant cette « cascade ». Malgré ses remarquables succès, cette théorie ne rend pas compte d’événements rares, mais très intenses, observés dans les écoulements turbulents. Délicats à caractériser expérimentalement et à modéliser, ces phénomènes intermittents représentent évidemment un défi pour les ingénieurs lors du dimensionnement de la résistance des avions, des trains ou des éoliennes, par exemple. La présentation abordera la question de l’intermittence à travers trois expériences : l’un à L’Institut Néel (soufflerie TOUPIE), la seconde au CEA (cellule SHREK) et la troisième au CERN (jet GReC). Ces écoulements tirent parti des propriétés uniques de l’hélium au dessus et en dessous de sa transition superfluide. Nous présenterons une réponse expérimentale à la question ouverte sur l’existence d’une différence entre l’intermittence d’un fluide quantique et celle d’un fluide classique.

 

European Cryogenics Days
Geneve, Suisse,  June 9-10 (2016)

• GReC experiment : probing ultra high-intensity turbulence in CERN  presented by   P. Roche

After one decade of hibernation and few key improvements, the turbulence experiment GReC was re-started in 2015, thanks to EC support (Consortium of European High-Performance Infrastructure in Turbulence, EuHit). This experiment consists in a 1-m-diameter jet of helium at 5 K, with a mass flow ranging from 20 to 250 g/s supplied by a 6 kW refrigerator. Academic-grade turbulence is generated at ultra high Reynolds numbers (Re>10^7), out-of-reach in standard laboratory experiments. What makes cryogenic helium so beneficial to turbulence studies ? What is the price to pay on the instrumentation side ? The talk will address and illustrate these points with preliminary results obtained in GReC.

 

 

EuHIT Turbulence Conference
Gottingen, Germany,  May 2-4 (2016)

• Multipoint micromachined network of cold wires  presented by   J. Valentin

The design and first fabrication and characterization results of a new micromachined cold wires sensor are presented. The sensor is dedicated to fast, high spatial resolution, low invasive and multipoint temperature measurements in turbulent flows. The sensors are made from silicon substrates, temperature is measured on suspended silicon nitride microwires. One sensor contains several measuring spots separated by length of the order of one millimetre. The main scientific motivations and design aspects are presented : sensor invasiveness in a flow, time and space resolution, electrical properties, thermometric materials, temperature sensitivity, mechanical stiffness, first tests and project perspective.

 

 

Top of the page

In 2015

 

Euhit cryogenic turbulence workshop
Grenoble, France  Oct 26th - 29th (2015)

• Cantilever and Pitot tube anemometers  presented by   E. Rusaouen
• Results from SHREK during its first EuHIT access  presented by   J. Burguete
• The CERN Cryogenic Turbulence Facility and the Tritium project  presented by   P.-E.R.
• He II co-flows  presented by P.-E.R.

 

Workshop on Interpretation of measurements in superfluid turbulence
Saclay, France  Sept 14th - 18th (2015)

• Micro-machined cantilever anemometer : Measurements in cryogenic turbulence  presented by   E. Rusaouen

As cryogenic turbulence involves a large range of different length scales and the environmental conditions are binding, it is necessary to imagine new kinds of sensors. Here, I will present a new silicon-based anemometer, typical length 375 microns, which provides the signed velocity at low temperatures. It operates from room temperature down to liquid helium temperature. This probe is developed within the EuHit project.

 

• Large-scale vortical motions in thermal counterflow around an obstacle  presented by   E. Lévêque

When a cylinder is placed in a counterflow channel, large-scale vortical structures appear on both sides of the cylinder, as originally vizualised by Zhang and Van Sciver (Nature Physics 1, 36-38 (2005)). Within the framework of the two-fluid model, we investigate the role played by the mutual friction (between the normal-fluid and superfluid components) in the apparition and dynamics of these structures.

 

• The T1 transition in counterflow : puzzle and geometrical artefact  presented by   P.-E.R.

The T1 counterflow transition has been studied for half a century and more than a dozen of theoretical models have been proposed to explain it. Still, experimentalists failed to conclusively decide among them due to unexplained scattering of measurements. Firstly, we will shortly review contradictory models and measurements of the T1-transition velocity threshold. Secondly, we propose a new criterion supported by numerical simulations, which suggests that part of the experimental scattering could result from a simple geometrical artefact.

 

• ???  presented by   J. Salort

xxx

 

15th European Turbulence Conference 2015
Delft, The Netherlands  Aug 25th - 28th (2015)

• Local heat flux measurements using a micro-machined integrated probe  presented by   E. Rusaouen
• Slow Dynamics in turbulent Helium flows  presented by   J. Burguete
• Local velocity measurements in the Shrek experiment at high Reynolds number  presented by   P. Diribarne et I. Moukharski
• Inter-vortex spacing in superfluid turbulence : temperature and Reynolds number dependences  presented by   P.-E. R.

 

International Conference on Rayleigh-Bénard Turbulence 2015
Göttingen, Germany  June 1th - 5th (2015)
• XXX  presented by   xxx

...

 

Top of the page

In 2014

 

67th Annual Meeting of the APS Division of Fluid Dynamics
San Francisco, California,  Nov 23th, (2014)
• Slow dynamics at Re=1E8 in turbulent Helium flows  presented by   J. Burguete

The presence of slow dynamics is a recurrent feature of many turbulent flows. This behaviour can be created by instabilities of the mean flow or by other mechanisms [1,2]. In this work we analyze the behavior of a highly turbulent flow (maximum Reynolds number Re=10^8, with a Reynolds based on the Taylor microscale Re_lambda=2000). The experimental cell consists on a closed cavity filled with liquid Helium (330 liters) close to the lambda point (between 1.8 and 2.5 K) where two inhomogeneous and strongly turbulent flows collide in a thin region. The cylindrical cavity has a diameter of 78cm and two impellers rotate in opposite directions with rotation frequencies up to 2Hz. The distance between the propellers is 70cm. Different experimental runs have been performed, both in the normal and superfluid phases. We have performed velocity measurements using home-made Pitot tubes. Here we would like to present preliminary results on this configuration. The analysis of the data series reveals that below the injection frequencies there are different dynamical regimes with time scales two orders of magnitude below the injection scale. Ref.[1] A. de la Torre, J. Burguete, Phys Rev Lett 99 (2007) 054101. [2] M. Lopez-Caballero, J. Burguete, Phys Rev Lett 110 (2013) 124501.

 

10th European Fluid Mechanics Conference EFMC
Copenhagen, Danmark,  Sept 14th - 18th (2014)
• Turbulent flow of superfluid helium in channels and effective viscosity in quantum turbulence: experiments and simulations  presented by   S. Jackson

...

 

23rd International Conference of Discrete Simulation of Fluid Dynamics
Paris, France,  July 28th - Aug 1st (2014)
• Lattice Boltzmann scheme for superfluid 4He dynamics  presented by   J. Bertolaccini

The superfluid phase of 4He (referred to as He-II) is a macroscopic quantum fluid with a number of extraordinary transport properties. Following the seminal work of Tsiza and Landau (1941) [1], He-II may be viewed at a macroscopic level as the binary mixture of a normal fluid with viscosity and entropy, and a superfluid without viscosity and entropy. At low Mach number, the resulting dynamics is governed by a system of Navier-Stokes and Euler equations coupled by a (modeled) mutual force that encompasses the interaction between the elementary constituents of the (mixed) two fluids at a microscopic level. During the conference, we will argue that the Lattice Boltzmann method provides a physically-sound framework to discretize the dynamics of He-II. A specific two-population scheme has been derived to handle the coupled dynamics of the normal-fluid and superfluid components [2]. This scheme is consistent (through a Chapman-Enskog expansion) with the macroscopic dynamics of He-II [3]. Furthermore, we will show that the mesoscopic nature of the Lattice Boltzmann method is particularly adequate to handle the exchange of momentum and heat with boundaries. This numerical scheme allows us to simulate superfluid counter-flow dynamics [4], in the presence of walls and obstacle, which is of fundamental interest in the understanding of superfluid dynamics. This approach also offers a high potential in simulating cryogenic flow, in which superfluid 4He is usually used as a very efficient coolant. To the best of our knowledge, Lattice Boltzmann scheme for superfluid 4He dynamics has never been investigated before.

 

ESF Workshop – Reconnection Events in Classical, Quantum and Magnetized fluids
Glasgow, Scotland,  June 16th-18th (2014)
• Investigation of turbulence in superfluid : top-down versus bottom-up approaches  presented by   P.-E. R.

Superfluid turbulence is been investigated using a variety of experimental approaches. Among them, one consist in probing its vortex-line density and its velocity fluctuations. We discuss the relative benefit of two quantities and illustrate how they offer overlapping perspectives in the study of superfluid turbulence, but don't fully match yet into a consistent quantitative description.

 

Quantum Turbulence and Its Visualization
Abu Dhabi, UAE  May 5-7th (2014)
• Application of small sensors   presented by   P.-E.R.

Strengths and Weaknesses of sub-millimeter sensors for probing/mapping He-II turbulent flows

 

42e Congrès National d'Analyse Numérique CANUM 2014
Carry-le-Rouet, France,  Mars 31st - April 4th (2014)
• Problèmes ouverts en turbulence des superfluides : point de vue d'un expérimentateur  presented by   P.-E. Roche

En dessous d'une température de transition superfluide, certains liquides entrent dans une phase quantique. Ils acquièrent alors des propriétés remarquables dont celle de pouvoir s'écouler sans présenter d'effet visqueux et de concentrer leur vorticité sur des filaments. Dès 1955, Richard Feynman a introduit le concept de ``turbulence superfluide'', encore appelé ``turbulence quantique'' pour évoquer la dynamique chaotique de ces écoulements, mais il a fallu attendre près d'un demi siècle pour qu'expérimentateurs, numériciens et théoriciens s'emparent en laboratoire de ce concept. Après une brève introduction à l'hydrodynamique des superfluides, illustrée par des expériences récentes menées avec de l'hélium, l'exposé introduira les 3 modèles mathématiques utilisée pour décrire ces écoulements, puis présentera quelques problèmes ouverts concentrant l'essentiel des efforts actuels.

 

Top of the page

In 2013

 

13^thWorkshop on Nonlocality in turbulence
Wolfgang Pauli Institute, Vienna, Austria  Dec. 2-5 (2013)
• Energy spectra and characteristic scales of quantum turbulence investigated by numerical simulations of the two-fluid model  presented by   E. Lévêque

Quantum turbulence at finite temperature (within the framework of the two-fluid model) exhibits an "anormal" distribution of kinetic energy of its superfluid component at scales larger than the inter-vortex distance. This anormal behavior is consistent with a thermalization of superfluid excitations at small scales. An original phenomenological argument allows us to predict explicitly the extension of the thermalization range. It is predicted that this extension is independent of the Reynolds number, and scales as the inverse square root of the normal fluid fraction. The prediction is well supported by high-resolution pseudo-spectral simulations of the two fluid-model.

 

13^th EUROMECH European Turbulence Conference
Lyon,   Sept. 1-4 (2013)

• Energy spectra and characteristic scales of quantum turbulence investigated by numerical simulations of the two-fluid model  by   P.-E. Roche et E. Lévêque
• First results of the shrek experiment at ultra-high reynolds number  by   C. Baudet et al.

 

Séminaire du Département de Physique de l'ENS Lyon
Lyon Feb 5th, 2013

• L’hydrodynamique des superfluides  presented by   P.-E. Roche

Brasser un pot de miel avec une cuillère est difficile, car la viscosité de ce fluide freine efficacement le mouvement. Par contre, dans un fluide moins visqueux comme le café dans une tasse, un simple mouvement de cuillère donne naissance à une multitude de tourbillons turbulents. Malgré les apparences, la viscosité du café continue toutefois de jouer un rôle central en freinant très efficacement les tourbillons les plus petits, et in-fine, en dissipant toute l'énergie cinétique communiquée initialement par le mouvement de la cuillère. Qu'advient-il si l'on brasse un fluide ne présentant strictement aucune viscosité ? Un liquide exotique permet d'étudier concrètement cette question : l'hélium superfluide. En dessous d’environ 2 K, l'hélium liquide entre en effet dans une phase quantique où il acquiert des propriétés remarquables dont celle de pouvoir s'écouler sans présenter d'effet visqueux. Après une introduction historique sur l’hydrodynamique des superfluides, l’exposé s’intéressera à la limite turbulente qui concentre l’essentiel des recherches actuelles. En particulier, on illustrera comment des études théoriques, numériques et expérimentales -parfois contradictoires- laissent toutes entrevoir une grande richesse phénoménologique de la turbulence des superfluides.

Top of the page

 

In 2012

 

Colloquium du Laboratoire de Physique de l'ENS Lyon
Lyon Dec 17th, 2012 (11h00)

• Turbulence d'une pelote de vortex superfluides  presented by   P.-E. Roche

Il est difficile de brasser un pot de miel avec une cuillère car la viscosité de ce fluide freine efficacement tout écoulement. Par contre, dans un fluide moins visqueux comme dans le café d'une tasse, un simple mouvement de cuillère génèrera des tourbillons de différentes tailles : l'écoulement est "turbulent". Malgré les apparences, la viscosité du café continue toutefois de jouer un rôle central en freinant très efficacement les tourbillons les plus petits, et in-fine, en dissipant toute l'énergie cinétique de l'écoulement. Qu'advient-il si l'on brasse un fluide ne présentant strictement aucune viscosité ? Un liquide exotique permet d'aborder cette question : l'hélium superfluide. En dessous de 2,17 K, l'hélium liquide entre en effet dans une phase quantique et il acquiert des propriétés remarquables dont celle de pouvoir s'écouler sans présenter d'effet visqueux. Dès 1955, Richard Feynman a introduit ainsi le concept de "turbulence quantique", encore appelé "turbulence superfluide", mais il a fallu attendre près d'un demi siècle pour qu'expérimentateurs, numériciens et théoriciens s'emparent en laboratoire de ce concept. Après une introduction générale, l'exposé présentera des progrès récents obtenues expérimentalement et par simulations numériques. En particulier, le concept de cascade de Kolmogorov sera revisité dans le cadre du modèle "à deux fluides" des écoulements quantiques.

 

European meeting : Superfluid turbulence from the perspective of numerics: modeling, methods and challenges
Centre Blaise Pascal, ENSL-Lyon, France  Nov 26-28 (2012)

• Continuous two-fluid model with a circulation-quantum-consistent truncation  presented by   J. Salort

 

Séminaire du Master recherche parcours Physique de la Matière Condensée
Orsay Sept 26th, 2012 (13h30)

• La turbulence quantique  presented by   P.-E. Roche

Il est difficile de brasser un pot de miel avec une cuillère car la viscosité de ce fluide freine efficacement tout écoulement. Par contre, dans un fluide moins visqueux comme dans le café d'une tasse, un simple mouvement de cuillère génèrera des tourbillons de différentes tailles : l'écoulement est "turbulent". Malgré les apparences, la viscosité du café continue toutefois de jouer un rôle central en freinant très efficacement les tourbillons les plus petits, et in-fine, en dissipant toute l'énergie cinétique de l'écoulement.
Qu'advient-il si l'on brasse un fluide ne présentant strictement aucune viscosité ? Un liquide exotique permet d'aborder cette question : l'hélium superfluide. En dessous de 2,17 K, l'hélium liquide entre en effet dans une phase quantique et il acquiert des propriétés remarquables dont celle de pouvoir s'écouler sans présenter d'effet visqueux. Dès 1955, Richard Feynman a introduit ainsi le concept de "turbulence quantique", encore appelé "turbulence superfluide", mais il a fallu attendre près d'un demi siècle pour qu'expérimentateurs, numériciens et théoriciens s'emparent en laboratoire de ce concept.
Après une introduction générale, l'exposé dressera un panorama international de cette activité et présentera quelques-uns des principaux défis relevés par les chercheurs. Le propos sera illustré par une présentation de progrès très récents.

 

10èmes Journées de Cryogénie et de Supraconductivité
Aussois, France,  Juin 5-8 (2012)

• Hydrodynamique et Turbulence superfluide  presented by   P.-E. Roche

Pour décrire l'écoulement d'un fluide visqueux, tel que l'eau, l'air, l'hélium gazeux ou l'He-I, un paramètre hydrodynamique joue un rôle central : le nombre de Reynolds. A l'aide de ce nombre et à partir d'abaques universels, on estime par exemple les pertes de charge le long d'une conduite, le coefficient de trainée d'une aile ou une condition de stabilité d'un écoulement. En dessous de sa transition superfluide, l'hélium 4He liquide (He-II) peut être décrit comme un mélange de deux composantes: un fluide « normal » visqueux et un autre «superfluide », capable de s’écouler sans viscosité. Comment prédire les propriétés des écoulements d'hélium superfluide ? En particulier, peut-on utiliser les connaissances acquises sur la turbulence des fluides visqueux ? Le nombre de Reynolds du superfluide est a priori infini puisqu’il est inversement proportionnel à sa viscosité. l'utilisation directe des abaques classiques est donc impossible. Toutefois, il y a une vingtaine d'années, des études expérimentales motivées par la refroidissement des bobines supraconductrices (LHC, ) ont rapporté que la perte de charge d'une conduite d'He-II est correctement estimée avec les abaques classiques, sous réserve de prêter au superfluide une viscosité finie. L'exposé présentera une série d'études récentes, expérimentales et numériques, de la turbulence de l'He-II apportant un éclairage nouveau sur cette problématique. En particulier, on montrera comment –sous certaines conditions, les écoulements superfluides turbulents présentent une viscosité apparente.

 

Workshop on Quantum Turbulence in Two Fluid Systems
Abu Dhabi, UAE, May 21-23 (2012)

• Can one infer the temperature of a turbulent superfluid using a millimeter-resolution anemometer ?  presented by   P.-E. Roche

In superfluid 4He wind-tunnels, high-Re flows can be generated over the temperature range 2.17 - 1.3 K, which corresponds to a superfluid fraction adjustable between 5% and 95%. Over this range, the properties of turbulence should evolve continuously, as the normal fluid vanishes and the superfluid becomes prevalent. The talk will address the following question : "How does the change in the balance of two fluids affect the Kolmogorov cascade and modify the turbulent fluctuations of He-II ?". The discusion will be nourished with numerical and experimental results.

 

New challenges in turbulence research
Les Houches, France,  March 18-23 (2012)

• Turbulence of superfluid ⁴He : a tour of 6 experiments and 1 simulation  presented by   P.-E. Roche

This lecture will present 6 experiments and 1 simulation of ⁴He turbulence at finite temperature. Phenomenological and quantive aspects of "the two-fluid casade" will be introduced step by step, to interpret the outcome of each experiment, orpresent challenges in our understanding of superfluid turbulence.

 

Top of the page

In 2011

 

GDR Turbulence
Aussois, France Dec. 12-14 (2011)

• Convection  presented by   P.-E. Roche

 

Meeting on cryoelectronic devices - Kryo 2011
Autrans, France, October, 2-4 (2011)

• Superfluid velocity measurements with a superconducting micro-resonator  presented by   J. Salort

 

13^th EUROMECH European Turbulence Conference
Warsaw, Poland,   Sept. 12-15 (2011)

• The Ultimate Regime of Convection over uneven plates  by  R. Kaiser et al.
• Micro-cantilever Anemometer for Cryogenic Helium  by   A. Monfardini et al.
• Experimental spectra of quantum turbulence for various flows  by   J. Salort et al.
• Vorticity scattering measurements in a superfluid inertial round jet  by   D. Duri et al.
• Kolmogorov cascade and equipartition of kinetic energy in numerical simulation of Superfluid turbulence  by   P.-E. Roche et al.

 

4th Workshop on the Physics and Applications of Superconducting Microresonators
St Martin d'Hères, France, July, 28-29 (2011)
• Miniature velocity probe for superfluid turbulence  presented by   J. Salort

 

Topical Meeting on Nanomechanic
Institut Néel, Grenoble, May 23 (2011)
• Design and Micro-machining of a Cryogenic Cantilever Anemometer for Superfluid Turbulence  presented by   J. Salort

 

Workshop on Classical and Quantum Turbulence
Abu Dhabi, UAE, May 2-5 (2011)

• Recent results for statistics in turbulent Helium II  presented by   J. Salort
• High Reynolds simulations of the 2-fluids continuous equations with a quantum-of-circulation-consistent numerical truncation  presented by   P.-E. Roche
• Cryogenic Cantilever Anemometer  presented by   J. Salort
• Local probes  presented by   P.-E. Roche

 

2nd PTA Users Meeting
Minatech, Grenoble, Jan. 24 (2011)

• Micro-poutrelle comme anémomètre pour la turbulence superfluide  presented by   J. Salort

 

 

Top of the page

In 2010

 

GDR Turbulence
Paris, France Nov. 3-5 (2010)
• Le principe des anémomètres à base de cantilevers; l'apport des techniques de salle blanche pour l'instrumentation hydro   presented by   J. Salort

 

Séminaire Néel
Grenoble Oct 19th, 2010 (11h00)

• Turbulence d'une pelote de vortex quantiques  presented by   P.-E. Roche

En dessous de 2,17 K, l'hélium liquide acquiert des propriétés superfluides. Il peut alors s'écouler sans viscosité et les "tourbillons" de son champ de vitesse se concentrent sur vortex quantiques. Dès 1955, R. Feynman attira l'attention sur la dynamique chaotique que devait présenter une pelote de vortex quantiques ; il introduisit ainsi le concept de "turbulence superfluide". Les études en laboratoire n'ont toutefois connu un véritable essor que depuis une dizaine d'années. Pour sonder cette turbulence superfluide, nous mettons en œuvre une approche originale associant mesures locales de fluctuations et simulations numériques sur supercalculateurs. Cette approche, et ses récents succès, seront présentés.

 

Meeting on Quantum Turbulence
Grenoble, France Aug. 7 (2010)

• Turbulent statistics in He-I versus He-II : comparison in various flows  presented by   J. Salort

 

International Symposium on Quantum Fluids and Solids
Grenoble, France Aug. 1-7 (2010)

• Velocity spectra in Turbulent He II  poster by   J. Salort
• Turbulent Convection : does the Ultimate Regime really follow Kraichnan prediction ?  poster by   P.-E. Roche
• Superfluid High Reynolds number von Karman experiment  poster by   B. Rousset

 

International workshop on Vortices, Superfluid dynamics and Quantum turbulence
Lammi, Finland Apr. 11-16 (2010)

• Local anemometers for Superfluid Turbulence  poster by   J. Salort
• ⁴He at finite temperature : DNS of homogeneous Superfluid Turbulence  presented by   P.-E. Roche

 

New challenges in turbulence research
Les Houches, France,  Feb. 21-26 (2010)

• Local sensors for cryogenic helium experiments  presented by   J. Salort
• Helium for Turbulence Research : overview of a few opportunities  presented by   P.-E. Roche

 

High Ra convection and Beyond
Les Houches, France,  Jan. 25-29 (2010)

• Ultimate regime Vs. Kraichnan regime  presented by   P.-E. Roche

 

 

 

Top of the page

In 2009

 

12^th EUROMECH European Turbulence Conference
Marburg,  Sept. 7-10 (2009)

• Convection at very high Rayleigh number: signature of transition from a micro-thermometer inside the flow  presented by   J. Salort
• TSF Experiment for comparison of high Reynold's number turbulence in He-I and He-II : first results  presented by   P. Diribarne
• Turbulent cascade of a quantum fluid at finite temperature  presented by   P.-E. Roche
• Shot noise of thermal plumes : Evidence of a boundary layer instability consistent with the onset of Kraichnan's Regime of convection  presented by   P.-E. Roche

 

Workshop on Experiments for Particles in Turbulence (Cost Action MP0806 WP1)
Zurich,  Aug 26-28 (2009)

• Local thermometry  to be presented by   P. E. Roche

 

International Conference on Complexity in Physics
Lyon,  June 1-5 (2009)

• The Ultimate Regime of Convection (with belt and braces)  to be presented by   P. E. Roche

 

Workshop on Topics in Quantum Turbulence
ICTP, Trieste,  March 16-20 (2009)

• Velocity spectra from various He-II flows at finite temperature  presented by   P. E. Roche

 

 

Top of the page

In 2008

 

61st Annual Meeting of the APS Division of Fluid Dynamics
San Antonio, TX,  Nov. 23-25 (2008)

• Classical Vs. Superfluid Turbulence  presented by   P. E. Roche

 

Workshop on Visualizing Thermo-Fluid Dynamics at Low Temperature
San Antonio, TX,  Nov. 19-21 (2008)

• Imaging LHe with neutrons, photons and CPU  presented by   P. E. Roche

 

Seminaires Dautreppe
Grenoble,  Oct 20-23 (2008)

• Le Régime Ultime de la convection (fete ses 10 ans de controverse)  presented by   P. E. Roche

 

Inertial-Range Dynamics and Mixing
Cambridge,  Sept. 29-Oct 3 (2008)

• The Spectrum of vortex density in a turbulent superfluid : Interpretation of a recent experiment  presented by   P. E. Roche

 

Condensed Matter and Materials Physics
Royal Holloway, UK,  March 26-28 (2008)

• Quantum Turbulence experiments in Grenoble : Turbulent fluctuations of superfluid vortices  presented by   P. E. Roche

 

 

Top of the page

In 2007

 

Second International Workshop on CICLoPE
Bertinoro,  Oct. 13-15 (2007)

• High Reynolds number pipe flow using cryogenic flow  presented by   P. E. Roche

 

CEC / ICMC
July, 16-20 (2007)

• Experimental facility for comparison of high Reynolds number turbulence in both HeI and HeII : first results  presented by   B. Rousset

 

11^th EUROMECH European Turbulence Conference
Porto, Portugal,  June 25-28, (2007)

• Probing Vortex Density Fluctuations in Superfluid Turbulence  presented by   P. E. Roche
• Ultimate regime of convection: search for a hidden triggering parameter  presented by   F. Gauthier

 

European Workshop on Turbulence in Cryogenic HElium
CERN, Geneva,  April 23-25 (2007)

• He hydrodynamic facilities used and in preparation at CERN presented by P.-E. Roche
• Fluid Mechanics with Helium: A Few Examples presented by B. Castaing
• Large scale He hydrodynamic facilities at CEA/SBT presented by B. Rousset

 

Introduction à l'hydrodynamique cryogénique
Conférence du département de physique de l'École Normale Supérieure de Lyon, ENS-Lyon (Séminaire video online)   April 18 (2007)

Les propriétés thermodynamiques très singulières de l'hélium à basse température (quelques degrés Kelvin) permettent de produire en laboratoire des écoulements modèles inaccessibles aux expériences traditionnelles. Après une introduction à cette discipline - l' hydrodynamique cryogénique- nous illustrerons son apport à deux problèmes ouverts en turbulence. D'abord, par le biais d'une controverse, toujours vive, sur le régime de la convection thermique attendu dans les écoulements géophysiques (atmosphère, océans, ...). Ensuite, sur le problème plus académique de la dynamique d'une pelote de vortex, telle un plat de spaghetti, et dont chaque élément de longueur entraînerait en rotation tous les autres selon une loi de type Biot et Savart.

Top of the page