Abstract
Tangles of a quantized vortex line of initial density L(0)∼6×10^{3} cm^{-2} and a variable amplitude of fluctuations of flow velocity U(0) at the largest length scale are generated in superfluid ^{4}He at T=0.17 K, and their free decay L(t) is measured. If U(0) is small, the excess random component of the vortex line length first decays as L∝t^{-1} until it becomes comparable with the structured component responsible for the classical velocity field, and the decay changes to L∝t^{-3/2}. The latter regime always ultimately prevails, provided the classical description of U holds. A quantitative model of coexisting cascades of quantum and classical energies describes all regimes of the decay.
Highlights
Tangles of a quantized vortex line of initial density Lð0Þ ∼ 6 × 103 cm−2 and a variable amplitude of fluctuations of flow velocity Uð0Þ at the largest length scale are generated in superfluid 4He at T 1⁄4 0.17 K, and their free decay LðtÞ is measured
If Uð0Þ is small, the excess random component of the vortex line length first decays as L ∝ t−1 until it becomes comparable with the structured component responsible for the classical velocity field, and the decay changes to L ∝ t−3=2
Turbulent flow in classical fluids can be described [1] as a superposition of coherent vortices, possessing a large nonequilibrium energy and responsible for the cascade of this energy towards smaller length scales, and a random incoherent flow, which is in equilibrium and dissipates at the smallest scales by viscosity
Summary
Turbulent flow in classical fluids can be described [1] as a superposition of coherent vortices, possessing a large nonequilibrium energy and responsible for the cascade of this energy towards smaller length scales, and a random incoherent flow, which is in equilibrium and dissipates at the smallest scales by viscosity. Tangles of a quantized vortex line of initial density Lð0Þ ∼ 6 × 103 cm−2 and a variable amplitude of fluctuations of flow velocity Uð0Þ at the largest length scale are generated in superfluid 4He at T 1⁄4 0.17 K, and their free decay LðtÞ is measured.
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