Experimental Investigation of Vortex Shedding in Superfluid $^4$He

TL;DR

This study experimentally investigates vortex shedding from an airfoil in superfluid helium, revealing that vortex behavior differs from theoretical predictions due to viscous and three-dimensional effects, with no significant difference between He I and He II.

Contribution

It provides the first detailed experimental analysis of vortex shedding in superfluid helium at an angle of attack of 49.1°, comparing behaviors in He I and He II.

Findings

No difference in vortex behavior between He I and He II.

Vortex trajectories deviate from theoretical models, moving faster and exhibiting unexpected deviations.

Viscous and 3D effects influence vortex dynamics in superfluid helium.

Abstract

During this internship, the starting vortex and its shedding from the trailing edge of an airfoil moving at constant acceleration in $^4$He has been studied. The airfoil has an angle of attack of 49.1{\deg} and corresponds to the NACA 0012, in contrast to most of the simulations using an angle of attack of 90{\deg} with a flat plate. An optical access combined with force and torque sensors enabled the study of this phenomenon. Particles are added to the fluid andfrom their position and velocity we obtained an estimate of the vorticity field. A tracking algorithm could then detect and track the vortex. From this tracking, we found no difference in the behaviour of the vortices in HeI and HeII. Furthermore, the trajectories do not correspond to the theoretical expectations, exhibiting straight trajectories until the vortex is independant of the airfoil, when a deviation in the trajectory happens. The vortex also moves faster than predicted. The differences are attributed to viscous and 3D effects.