A5029243356- Fluid Dynamics and Turbulent Flows
- Quantum, superfluid, helium dynamics
- Spacecraft and Cryogenic Technologies
- Combustion and flame dynamics
- Meteorological Phenomena and Simulations
- Phase Equilibria and Thermodynamics
- Advanced Thermodynamics and Statistical Mechanics
- Gas Dynamics and Kinetic Theory
- Plant Water Relations and Carbon Dynamics
- Solar and Space Plasma Dynamics
- Heat Transfer and Boiling Studies
- Particle Dynamics in Fluid Flows
- Heat Transfer Mechanisms
- Superconducting Materials and Applications
- Atomic and Subatomic Physics Research
- Supramolecular Self-Assembly in Materials
- Photochromic and Fluorescence Chemistry
- nanoparticles nucleation surface interactions
- Complex Systems and Time Series Analysis
- Nonlinear Dynamics and Pattern Formation
- High-pressure geophysics and materials
- Wind and Air Flow Studies
- Engineering Diagnostics and Reliability
- Luminescence and Fluorescent Materials
- Click Chemistry and Applications
Centre National de la Recherche Scientifique
2000-2023
Institut Néel
2008-2023
Université Grenoble Alpes
2011-2023
Département de Chimie Moléculaire
2021-2022
Université Claude Bernard Lyon 1
2017
Université Joseph Fourier
1997-2011
Institut Universitaire de France
2000
Technion – Israel Institute of Technology
1995
In a low temperature He gas Rayleigh-B\'enard experiment, Rayleigh numbers from ${10}^{3}$ to more than ${10}^{14}$ are explored. Local velocity is estimated through the time lag between two closeby probes. This allows characterizing of high regime $(\mathrm{Ra}>{10}^{11})$ as fully turbulent one, possibly corresponding asymptotic predicted by R. Kraichnan [Phys. Fluids 5, 1374 (1962)].
In this article we deal with the turbulent regimes of Rayleigh–Bénard convection, namely 2/7 regime and beyond. An experiment He at low temperature allows us to explore a large Rayleigh number (Ra) range up 2×1014, under Boussinesq conditions, while Prandtl (Pr) is equal larger than 0.7. Calorimetric measurements evidence departure from above Ra=1011 toward new where heat transfer enhanced. Local two nearby thermometers relate change laminar–turbulent transition velocity boundary layer...
A summary of experimental results on structure functions obtained using extended self-similarity in various flow configurations (jet, grid, mixing layer, duct flow, cylinder) at Reynolds numbers ranging between 30 and 5000 is presented.
We present velocity spectra measured in three cryogenic liquid H4e steady flows: grid and wake flows a pressurized wind tunnel capable of achieving mean velocities up to 5 m/s at temperatures above below the superfluid transition, down 1.7 K, “chunk” turbulence flow 1.55 sustaining 1.3 m/s. Depending on flows, stagnation pressure probes used for anemometry are resolving from one two decades inertial regime turbulent cascade. do not find any evidence that second-order statistics transition...
The $\frac{1}{2}$ power law is reported in a Rayleigh-B\'enard experiment: ${\mathrm{Nu}\mathrm{\ensuremath{\sim}}\mathrm{Ra}}^{1/2},$ where Ra and Nu are the Rayleigh Nusselt numbers. This observation coherent with predictions of ultimate convection regime, characterized by fully turbulent heat transfers. Ordered rough boundaries used to cancel correction due thickness variation viscous sublayer, asymptotic regime therefore possible. result supports interpretation laminar-turbulent...
Using an axisymmetric jet with helium at low temperature we have studied the velocity intermittency on a large range of Taylor scale based Reynolds number ${R}_{\ensuremath{\lambda}}$. The results show, for first time, evidence transition between two types turbulence in jet. Above (${R}_{\ensuremath{\lambda}}>180$) clear separation occurs small and scales. In intermediate range, existence dependent scaling law is confirmed. It illustrates way which viscosity can some influence up close to...
The 4/5-law of turbulence, which characterizes the energy cascade from large to small-sized eddies at high Reynolds numbers in classical fluids, is verified experimentally a superfluid 4He wind tunnel, operated down 1.56 K and up R_lambda ~ 1640. result corroborated by high-resolution simulations Landau-Tisza's two-fluid model 1.15 K, corresponding residual normal fluid concentration below 3 % but with lower number order 100. Although K\'arm\'an-Howarth equation (including viscous term) not...
Using low-temperature gaseous helium close to the critical point, we investigate Prandtl-number dependence of effective heat conductivity (Nusselt number) for a 1/2 aspect ratio Rayleigh-Bénard cell. Very weak is observed in range 0.7 < Pr 21; 2 × 108 Ra 1010: absolute value average logarithmic slope δ = (∂ln Nu/∂ln Pr)Ra smaller than 0.03. A bimodality Nu, with 7% difference between two sets data, observed, which could explain some discrepancies precise previous experiments this range.
The proposed universality of small scale turbulence is investigated for a set measurements in cryogenic free jet with variation the Reynolds number (Re) from 8500 to 10(6) (max(R(lambda) approximately 1200). traditional analysis statistics velocity increments by means structure functions or probability density replaced new method which based on theory Markov processes. It gives access more complete characterization joint probabilities finding at several scales. Based this comprehensive...
The intermittency of turbulent superfluid helium is explored systematically in a steady wake flow from 1.28 K up to T&gt;2.18K using local anemometer. This temperature range spans relative densities superfluids 96% down 0%, allowing us test numerical predictions enhancement or depletion at intermediate fractions. Using the so-called extended self-similarity method, scaling exponents structure functions have been calculated. No evidence dependence found on these upper part inertial...
We have studied homogeneous cavitation in liquid nitrogen and normal helium. monitor the fluid content a large number of independent mesopores with an ink-bottle shape, either when pores is quenched to constant pressure or submitted decreasing at controlled rate. For both fluids, we show that, close enough their critical point, threshold good agreement Classical Nucleation Theory (CNT). In contrast, lower temperatures, deviations are observed, consistent reduction surface tension for bubbles...
This paper reports new experimental and simulation velocity data for superfluid steady turbulence above 1K. We present values the scaling exponent of absolute value velocity-increment structure functions. In both experiments simulations, they evidence that intermittency occurs in flows a quite comparable way to classical turbulence. particular, deviation from Kolmogorov 1941 keeps same strength as we cross transition. To best our knowledge, this is first confirmation 4He results Maurer &...
A micronic-size hot wire anemometer operating at cryogenic temperatures (4 K) has been developed; using superconducting and resistive thin films, its electrical resistance is very sensitive to the velocity of a gaseous 4He subsonic jet. The fabrication procedure described measured characteristics are compared with simple thermal equilibrium model.
A transition to Kraichnan ultimate regime of convection has been reported in very high Rayleigh numbers experiments, but not all them. These apparently contradictory results can be explained by a recent phenomenological model which accounts for the non-ideality plate thermal properties [Chill\`{a} et al, Physics Fluids 16:2452 (2004)]. In this paper, we present direct test model, using low conductivity plate. We found an unaltered transition, compatible with model's predictions.
Micronic-size thermometers (1.5×1.5×0.5 μm3) designed for local measurements in turbulent gaseous helium the range of 4–80 K, have been developed and tested. Their very short time response (⩽1 μs) micronic spatial resolution allow to perform down Kolmogorov dissipative length scale, high Reynolds or Rayleigh numbers flows. These thermometers, be nonperturbative flow, are based on Au–Ge thin films deposited by sputtering process drawn glass fibers. relative sensitivities σ=|(T/R)(dR/dT)|...
APR'L 1994' ~~~~ ~~' Abstract. For turbulent studies in gaseous 4He at 4 K, a micronic scale anenometer with broad band (~ l MHz ) has been developed. Typical results are presented, together possible extensions to cryogenic flowmetry applications. Open flow experiments govemed by the Reynolds number : file = UL/v U is mean velocity measured same place as L which some characteristic length for energy injection (the diameter of nozzle jet experiment example) and v kinematic viscosity, that...