Study shows the difference between classical flows and superfluid helium in 3-D counter-flow | 11/15/2012 | Staff
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Credit: Biferale et al.

Researchers at the Weizmann Institute of Science, the University of Rome, CNRS and the University of Helsinki have recently carried out a study investigating the difference between 3-D anisotropic turbulence in classical fluids and that in superfluids, such as helium. Their findings, published in Physical Review Letters (PRL), are supported by both theory and experimental evidence.

Research - Group - Weizmann - Institute - Israel

"The present research was initiated by our group at the Weizmann Institute, Israel, comprised by Victor L'vov, Itamar Procaccia and Anna Pomyalov, who were trying to understand novel experimental observations by the groups of Prof. Wei Guo from Florida State University, Tallahassee and Prof. Ladislav Skrbek from Charles University, in Prague," Itamar Procaccia, one of the researchers who carried out the study, told "Our main objective was to understand an apparent surprising difference in how energy distributes between turbulent eddies of different scales in classical viscous fluids like air and water and superfluids like helium at low temperatures."

All turbulent flows, both in nature and laboratory settings, are anisotropic on energy injection scales, meaning that energy distributes differently between their turbulent eddies. Past studies have shown that the model of homogeneous and isotropic turbulence (HIT) is particularly effective for predicting the statistical properties of turbulence on scales much smaller than stirring scales, yet larger than dissipative scales.

Fluids - Anisotropic - Turbulence - Towards - Isotropy

In classical fluids, 3-D anisotropic turbulence tends towards isotropy and homogeneity with decreasing scales, hence it is eventually possible to apply the HIT model to them. In their study, however, Procaccia and his colleagues demonstrated that the opposite is true for superfluid 4He turbulence in 3-D counter-flow channel geometry, which becomes less isotropic as scales decrease, to the point of becoming almost two-dimensional.

The approach used by them involves a so-called 'two-fluid model' of superfluid helium. This model is based on the early work of Laszlo Tisza...
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