Direct measurement of the energy dissipated by quantum turbulence

• Published in: Nature physics Vol. 7; no. 6; pp. 473 - 476
• Main Authors: Bradley, D. I., Fisher, S. N., Guénault, A. M., Haley, R. P., Pickett, G. R., Potts, D., Tsepelin, V.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01-06-2011; Nature Publishing Group
• Subjects: Atomic; Classical and Continuum Physics; Complex Systems; Condensed Matter Physics; Decay; Enthalpy; Fluid dynamics; Fluid flow; Fluids; letter; Mathematical and Computational Physics; Molecular; Navier-Stokes equations; Optical and Plasma Physics; Physics; Physics and Astronomy; Quantum theory; Quantum turbulence; Theoretical; Thermal energy; Turbulence; Turbulence models; Turbulent flow
• ISSN: 1745-2473; 1745-2481
• DOI: 10.1038/nphys1963

It is difficult to measure the turbulent energy in a classical system as the turbulence contributes only a small kinetic energy compared with the enthalpy of the system. A quantum system, however, such as liquid helium at absolute zero, has zero enthalpy. Added vorticity therefore accounts for the total energy, thus allowing the turbulent energy to be measured directly
The lack of a general solution to the governing Navier–Stokes equations means that there is no fundamental theory of turbulence. In the simpler case of pure quantum turbulence, the tangle of identical singly quantized vortices in superfluids at
T
∼0 may provide a deeper understanding of turbulence in general. The well-known Kolmogorov theory
1
predicts the energy distribution of turbulence and how it decays. In normal systems the turbulent energy is generally only a small perturbation on the total thermal energy of the supporting medium. In quantum turbulence, however, the energy is accessible. A stationary condensate is necessarily in its ground state with zero enthalpy. Thus quantum turbulence accounts for the entire free energy of the superfluid and there are no other contributions. Here, we exploit this property to make the first direct measurement of the energy released by freely decaying quantum turbulence. Our results are consistent with a Kolmogorov energy spectrum with an inferred Kolmogorov constant remarkably similar to those of classical fluids.