arXiv subjects

J. F. Pinton

Publications and source records attributed to J. F. Pinton.

3 recordsLinked to original sources

arXiv2006

Transport of magnetic field by a turbulent flow of liquid sodium

We study the effect of a turbulent flow of liquid sodium generated in the von Kármán geometry, on the localized field of a magnet placed close to the frontier of the flow. We observe that the field can be transported by the flow on distances larger than its integral length scale. In the most turbulent configurations, the mean value of the field advected at large distance vanishes. However, the rms value of the fluctuations increases linearly with the magnetic Reynolds number. The advected field is strongly intermittent.

physics.flu-dyn↗

arXiv2002

The alpha effect and its saturation in a turbulent swirling flow generated in the VKS experiment

We report the experimental observation of the alpha-effect. It consists in the generation of a current parallel to a magnetic field B0 applied to a turbulent swirling flow of liquid sodium. At low magnetic Reynolds number, Rm, we show that the magnitude of the alpha-effect increases like Rm2 and that its sign is determined by the flow helicity. It saturates and then decreases at large Rm, primarily because of the expulsion of the applied field B0 from the bulk of the flow. We show how this expulsion is affected by the flow geometry by varying the relative amplitudes of the azimuthal and axial flows.

physics.flu-dyn↗

arXiv2001

Time resolved tracking of a sound scatterer in a turbulent flow: non-stationary signal analysis and applications

It is known that ultrasound techniques yield non-intrusive measurements of hydrodynamic flows. For example, the study of the echoes produced by a large number of particle insonified by pulsed wavetrains has led to a now standard velocimetry technique. In this paper, we propose to extend the method to the continuous tracking of one single particle embedded in a complex flow. This gives a Lagrangian measurement of the fluid motion, which is of importance in mixing and turbulence studies. The method relies on the ability to resolve in time the Doppler shift of the sound scattered by the continuously insonfied particle. For this signal processing problem two classes of approaches are used: time-frequency analysis and parametric high resolution methods. In the first class we consider the spectrogram and reassigned spectrogram, and we apply it to detect the motion of a small bead settling in a fluid at rest. In more non-stationary turbulent flows where methods in the second class are more robust, we have adapted an Approximated Maximum Likelihood technique coupled with a generalized Kalman filter.

physics.flu-dyn↗