Experimentální a numerické studium kvantové turbulence v He II

Varga, Emil

Superfluid 4 He (He II) is a quantum liquid whose flow is strongly affected by quantum mechanical effects. This thesis presents experimental and numerical studies of turbulent flows in He II - quantum turbulence. Experimentally, quan- tum turbulence is investigated in thermal counterflow, pure superflow and coflow using second sound attenuation, precision local thermometry and by visualisa- tion of helium excimer molecules. The steady state and decay of the vortex line density in pure superflow and counterflow is studied and the universal quasi clas- sical decay is characterised by measurements of the effective kinematic viscosity. General dynamical behaviour is studied in detail in unsteady thermal counter- flow, with various theoretical models tested. A new model where the mean tangle curvature is dependent on the vortex line density is proposed. Temperature de- pendence and enhancement of intermittency in quasi-classical flow in the wake of a moving grid is found using visualisation. Numerically, the interaction of the tangle of quantized vortices with solid tracers is investigated, where a back reaction of the seeding particles on the tangle is identified and its relevance to visualisation experiments is discussed. Additionally, an interesting and as-yet overlooked spherical counterflow is...

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