Turbulent heat transport regimes in a channel

International audienceIn this paper we focus on the turbulent transport of a scalar through a channel. The scalar flux, and the corresponding scalar concentration gradient along the channel allow to define a Nusselt number and a Grashof number. While the relation between the large scale velocity field and the input energy rate show a perfect inertial (turbulent) behavior, three different regimes can be distinguished, with different scalings between Nusselt and Grashof numbers

Thermal transfer in Rayleigh-Bénard cell with smooth or rough boundaries

International audienceSeveral Rayleigh-Bénard experiments in water are performed with smooth or rough boundaries. We present new thermal transfer measurements obtained with large roughness elements arranged in a square lattice. The data are compared to previous ones obtained with smaller elements in the same cell (Tisserand et al., 2011). Experiments in the same apparatus without roughness are fully presented, as reference results, to allow for comparison. In the rough case, several regimes of heat transfer are identi ed : one similar to the smooth case, an enhanced heat transfer one characterized by a modi cation of the Nusselt vs Rayleigh numbers relation, and a third part where the relation can be similar to a smooth one with a corrected prefactor

A local sensor for joint temperature and velocity measurements in turbulent flows

International audienceWe present the principle for a micro-sensor aimed at measuring local correlations of turbulent velocity and temperature. The operating principle is versatile and can be adapted for various types of flow. It is based on a micro-machined cantilever, on the tip of which a platinum resistor is patterned. The deflection of the cantilever yields an estimate for the local velocity, and the impedance of the platinum an estimate for the local temperature. The velocity measurement is tested in two turbulent jets: one with air at room temperature which allows to compare with well-known calibrated reference anemometers, and another one in the GReC jet at CERN with cryogenic gaseous helium which allows a much larger range of resolved turbulent scales. The recording of temperature fluctuations is tested in the Barrel of Ilmenau which provides a controlled turbulent thermal flow in air. Measurements in the wake of a heated or cooled cylinder demonstrate the capability of the sensor to display the cross correlation between temperature and velocity correctly

Local velocity measurements in the Shrek experiment at high reynolds number

International audienceWe report preliminary results obtained using new local velocity probes in the Superfluid Helium high REynold number von Kármán flow (SHREK) experiment for different forcing conditions. The presentation will focus on the validation of the signals obtained from a hot-wire and a total head pressure tube in both normal and superfluid phases of liquid helium

Experimental Signature of Quantum Turbulence in Velocity Spectra?

International audienceVelocity measurements in turbulent superfluid helium between co-rotating propellers are reported. The parameters are chosen such that the flow is fully turbulent, and its dissipative scales are partly resolved by the velocity sensors. This allows for the first experimental comparison of spectra in quantum versus classical turbulence where dissipative scales are resolved. In some specific conditions, differences are observed, with an excess of energy at small scales in the quantum case compared to the classical one. This difference is consistent with the prediction of a pileup of superfluid kinetic energy at the bottom of the inertial cascade of turbulence due to a specific dissipation mechanism