Experimental Investigation of Oscillating-Grid Turbulence in Cryogenic Normal/Superfluid Helium 4
| When |
Sep 15, 2023
from 11:00 to 12:00 |
|---|---|
| Where | M7-101 |
| Attendees |
Clément Bret |
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Cooling helium gas to an extremely low temperature results in the formation of liquid helium (He I), the least viscous fluid of all. As the temperature is further lowered, below a critical value, it enters a second liquid phase (He II) which exhibits unexpected properties such as extremely high thermal conductivity or apparent absence of viscosity under certain conditions, leading the scientific community to refer to it as a "superfluid."
In my presentation, I will introduce the two-fluid model, which describes this unusual liquid as a combination of two components: a classical viscous component, referred to as the normal component, and a quantum non-viscous component, referred to as the superfluid component. Then, I will mainly focus on the experimental investigation of a turbulent flow in both He I and He II phases. I will center my discussion around results from the OGRES experiment (Oscillating Grid Experiment in Superfluid), which consists of a pair of oscillating grids that generate a nearly homogeneous, stationary, and isotropic turbulence. I will present preliminary results of 2x2D Particle Tracking Velocimetry (PTV) measurements revealing how turbulence intensity responds to different amplitudes (A_mot) and frequencies (f_mot) of mechanical forcing. Additionally, I will discuss 2nd sound attenuation measurements, which were employed to estimate the mean vorticity of the superfluid component in He II. Finally, I will show how these two independent measurements can be combined to determine the effective viscosity of the probed flow.