Dynamics of the density of vortex lines and thermal pulses in superfluid helium
Institute of Thermophysics, 1 Lavrentyev A ve, Novosibirsk 630090, Russia
National Research University "Moscow Power Engineering Institute" Krasnokazarmennaya 14, Moscow,
Received March 5, 2019, published online April 24, 2020
Numerically, in the framework of the hydrodynamics of superfluid turbulence, using various equations for the dynamics of the density of vortex lines, we study the propagation of intense rectangular thermal pulses in superfluid helium. It is shown that experimental data are more correctly described when the Vinen equation is applied. Using the Vinen equation to describe the dynamics of the density of vortex lines, we studied the effect of the background density of the vortex tangle on the dynamics of the pulses at different temperatures of the unperturbed fluid. It was established that the high background density of the vortex tangle leads to a significant change in the shape of the pulse and overheating of the liquid. At the same values of the supplied heat flux density to the heater and the background density of the vortex tangle, temperature perturbations decrease with increasing temperature of the unperturbed liquid. This is due to a change in the thermodynamic properties of the fluid and the dynamics of the vortex lines density. As the temperature increases, the density of the vortex tangle increases noticeably slower, and as a result of this the perturbations of the liquid temperature decrease significantly.
Key words: thermal pulses, waves of the second sound, superfluidity, vortex lines, quantum turbulence.