Intermittency of quantum turbulence with superfluid fractions from 0% to 96%

Abstract

Submitted to Physics of Fluids in 2017International audienceThe intermittency of turbulent superfluid helium is explored systematically in a steady wake flow from 1.28 K up to T > 2.18K using a local anemometer. This temperature range spans relative densities of superfluid from 96% down to 0%, allowing to test numerical predictions of enhancement or depletion of intermittency at intermediate superfluid fractions. Using the so-called extended self-similarity method, scaling exponents of structure functions have been calculated. No evidence of temperature dependence is found on these scaling exponents in the upper part of the inertial cascade, where turbulence is well developed and fully resolved by the probe. This result supports the picture of a profound analogy between classical and quantum turbulence in their inertial range, including the violation of self-similarities associated with inertial-range intermittency

Intermittency enhancement in quantum turbulence in superfluidHe4

“…Let us compare our results with similar experimental data available. The recent Grenoble measurements of Rusaouen et al [13] in the wake of a disk in the two- fluid region of superfluid 4 He found no appreciable temperature dependence in intermittency corrections. The results of the Grenoble experiment and our experiment therefore appear to be controversial.…”

“…Indeed, it has been predicted by Boué et al [10] and Biferale et al [12] that when probed at small scales, intermittency corrections to the scaling of higher-order velocity structure functions in He II quasi-classical turbulence should be enhanced in the temperature range 1.3 T 2.1 K, with a maximum deviation from the Kolmogorov-Obukhov K41 theory for classical turbulence [32] around 1.85 K. Early experiments conducted at low temperatures and close to T λ did not find deviations from the statistics of classical turbulence [9,33,34]. A more recent experiment in a turbulent wake in He II covered a wider range of temperatures but also reported temperature independent intermittency, similar to that in classical flows [13]. It should be noted, however, that the pressure and velocity probes used in these experiments all have sizes much larger than Q and hence are sensitive only for the corresponding part of the turbulent cascade [12,13].…”

Turbulent statistics and intermittency enhancement in coflowing superfluidHe4

“…The experiments [7][8][9] , conducted mostly at low temperatures and close to T λ , did not find deviations from the turbulent statistics of classical flows. A very recent experimental study 12 of turbulence in the wake of a disc was conducted in a wide range of temperatures; it also did not find any temperature dependence of the scaling exponent of the second order structure function. Preliminary results of the ongoing study 13 of turbulence behind a grid indicated a temperature dependence of higher-order structure functions scaling.…”

“…where D α (R) is given by Eq. To test its consistency with the original form, we consider (12) in the inertial interval of scales of the isotropic turbulence without helicity. First, we recall the most general form of J α,βγ in that case 24 :…”

Inviscid diffusion of vorticity in low-temperature superfluid helium

“…Most experimental, theoretical and numerical studies have addressed quantum turbulence in its simplest form: statistically-steady, homogeneous and isotropic. These studies have revealed similarities and differences with respect to ordinary turbulence, in terms of energy spectra [2][3][4], decay [5,6], intermittency [7][8][9] and velocity statistics [10][11][12]. Much less is known about turbulence which is inhomogeneous, in particular turbulence which is initially confined in a small region of space and is free to spread out.…”