Backreaction of Tracer Particles on Vortex Tangle in Helium II Counterflow

We report computer simulations of the interaction of seeding particles with quantized vortices and with the normal fluid flow in thermal counterflow of superfluid He. We show that if the number of particles is too large, the vortex tangle is significantly affected, posing problems in the interpretation of visualization experiments. The main effects are an increase in vortex line density and a change in polarization of the vortex tangle, caused by the action of the Stokes drag of the viscous normal fluid on the trapped particles. We argue that in the case of large particle number, typically used for the particle image velocimetry technique, the tangle properties might become significantly changed. On the contrary, the particle tracking velocimetry technique that uses smaller particle concentration should not be appreciably affected.