Direct numerical simulation of superfluid turbulence.
Item
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Title
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Direct numerical simulation of superfluid turbulence.
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Identifier
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AAI3330496
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identifier
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3330496
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Creator
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Morris, Karla.
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Contributor
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Advisers: Joel Koplik | Damian Rouson
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Date
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2008
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Language
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English
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Publisher
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City University of New York.
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Subject
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Physics, Condensed Matter | Physics, Fluid and Plasma | Engineering, Mechanical
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Abstract
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At low temperatures, as quantum effects become increasingly apparent, helium (He4) transforms into a superfluid. The motion of superfluid helium (He II) can be decomposed into two interpenetrating components: (1) an inviscid (superfluid) liquid containing line vortices with quantized circulation and (2) a (normal fluid) gas of elementary thermal excitations. At sufficiently high driving velocities, the motion of He II becomes unstable and transitions to turbulence, commonly termed superfluid turbulence or quantum turbulence. A growing body of empirical evidence suggests that the macroscopic statistical behavior of quantum turbulence closely matches that of classical turbulence despite considerable differences in the physics at the mesoscopic scale of the inter-vortex spacing and the microscopic scale of the vortex core diameters [47,50]. Although a commonly used phenomenology involving quantum-vortex/normal-vortex locking has achieved some success in explaining the macroscopic similarities, current laboratory measurements lack sufficient spatial resolution to verify vortex locking. The work presented here investigates the detailed mechanisms underlying quantum turbulence via direct numerical simulations (DNS) of superfluid vortex interactions with interpenetrating normal fluid turbulence. The driving fluid is the normal component which behaves as a statistically homogeneous isotropic turbulent flow, and both forced and decaying cases are simulated. The data obtained from the simulation is analyzed using wavelet transforms and velocity correlations. The normal fluid calculation employs a Navier-Stokes (NS) solver developed by Rouson and Xu [31] in a manner that facilitates rapid integration of new physics by expressing dynamical equations in forms very closely mirroring their analytical expression. The superfluid calculation employs a vortex filament method originated by Schwarz [39,40,41]. The Navier-Stokes and vortex filament equations are marched in time using a software module developed by Rouson, Morris and Xu [33] which facilitates rapid implementation of time advancement algorithms for coupled multi-physics problems.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
