The aim of this training period is the experimental study of the transition to turbulence in a superfluid He boundary layer (below 2.17K) at the surface of an oscillating plate. Superfluid helium is often described a mixture of two independent components: the normal component is viscous and governed by the standard Navier-Stokes equation while the superfluid component is inviscid.
The way those two components interact to form a boundary layer is poorly documented. In particular, below a critical Reynolds number (often associated to a velocity in the literature), it is expected that only the normal component is influenced by the presence of the moving plate. It is one of the hypothesis we shall address during the training period.

Full description of the subject The aim of this training period is the experimental study of the transition to turbulence in a superfluid He (below 2.17K) boundary layer at the surface of an oscillating plate. Superfluid helium is often described a mixture of two independent components: the normal component is viscous and governed by the standard Navier-Stokes equation while the superfluid component is inviscid.
The way those two components interact to form a boundary layer is poorly documented. In particular, below a critical Reynolds number (often associated to a velocity in the literature), it is expected that only the normal component is influenced by the presence of the moving plate. It is one of the hypothesis we shall address during the training period.

The work shall be divided into 3 parts:
- First the student will have to improve the experimental apparatus, introducing a frictionless guiding system for the oscillating plate, the current system with solid-solid friction (item 3 in the figure below) being replaced by permanent magnets plus superconductors. He should also install the visualization system. All these components are already available at lab.
- Then the student will perform measurements, based on "second sound acoustics" and visualization of the surrounding flow. Second sound attenuation measurement is a powerful way to detect the appearance of turbulence. The vorticity in a superfluid boundary layer can be detected thanks to the attenuation of the temperature waves (aka second sound) it will provoke. Those waves, superfluid specific, are the manifestation of the propagation of heat. Furthermore, visualization should help to detect any parasitic large scale flow induced by the oscillating plate. Then, once the turbulent state is reached, visualization should provide insight on its spatial development.
- Finally the student is expected to process the experimental data using a high level programming language (Matlab/Octave or Python). This is a very important task of the training period.

Required skills:
Fluid dynamics, Computer programming, Basics in electronics.

Keywords:
Boundary layer, Superfluid He, Second sound, Visualization.

Contact:
Diribarne Pantxo
Phone: +33 4 38 78 69 79