Search results for "superfluid helium"
showing 10 items of 46 documents
Vortex density waves and high-frequency second sound in superfluid turbulence hydrodynamics
2010
In this paper we show that a recent hydrodynamical model of superfluid turbulence describes vortex density waves and their effects on the speed of high-frequency second sound. In this frequency regime, the vortex dynamics is not purely diffusive, as for low frequencies, but exhibits ondulatory features, whose influence on the second sound is here explored.
On the existence of higher waves in a layer of superfluid helium
1973
The two implicit equations that contain the dispersion laws of waves propagating in a He II layer of variable thickness are formally investigated for solutions that go beyond those associated with the layer modifications of first and second sound: A series of symmetric and antisymmetric layer modes are found to exist by calculating the distribution of roots of the dispersion equations in the complex wave number plane as a function of layer thickness and angular frequency. All these modes turn out to be strongly attenuated and can be regarded as layer modifications of the viscous wave. Phase velocities, attenuation coefficients, and velocity profiles of some of them are calculated numericall…
Turbulent Superfluid Profiles and Vortex Density Waves in a Counterflow Channel
2012
In this paper we study the two-dimensional profiles of the superfluid component velocity and the quantized vortex-points density in a counterflow channel where the influence of the walls cannot be neglected. The numerical results obtained show the presence of vortex density waves in the channel, as shown in a recent paper by means of the one-fluid model.
Waves Propagation in Turbulent Superfluid Helium in Presence of Combined Rotation and Counterflow
2010
A complete study of the propagation of waves (namely longitudinal density and temperature waves, longitudinal and transversal velocity waves and heat waves) in turbulent superfluid helium is made in three situations: a rotating frame, a thermal counterflow, and the simultaneous combination of thermal counterflow and rotation. Our analysis aims to obtain as much as possible information on the tangle of quantized vortices from the wave speed and attenuation factor of these different waves, depending on their relative direction of propagation with respect to the rotation vector.
Longitudinal counterflow in turbulent liquid helium: velocity profile of the normal component
2013
In this paper, the velocity profile of the normal component in the stationary flow of turbulent superfluid helium inside a cylindrical channel is determined, making use of a one-fluid model with internal variables derived from Extended Thermodynamics. In the hypothesis of null barycentric velocity of the fluid (the so-called counterflow situation) it is seen that, in the presence of a sufficiently high vortex length density, the velocity profile of the normal component becomes very flat in the central region of the channel. Thus, a central flat profile of the normal fluid does not necessarily imply that the flow of the normal component is turbulent.
Waves on a vortex filament: exact solutions of dynamical equations
2014
In this paper we take into account the dynamical equations of a vortex filament in superfluid helium at finite temperature (1 K < T < 2.17 K) and at very low temperature, which is called Biot-Savart law. The last equation is also valid for a vortex tube in a frictionless, unbounded and incompressible fluid. Both the equations are approximated by the Local Induction Approximation (LIA) and Fukumoto's approximation. The obtained equations are then considered in the extrinsic frame of reference, where exact solutions (Kelvin waves) are shown. These waves are then compared one to each other in terms of their dispersion relations in the frictionless case. The same equations are then investigated…
CONDENSATE FRACTION IN THE DYNAMIC STRUCTURE FUNCTION OF BOSE FLUIDS
2007
We present results on the behavior of the dynamic structure function in the short wave length limit using the equation of motion method. The one-body continuity equation defines the self-energy, which becomes a functional of the fluctuating two-body correlation function. We evaluate the self-energy in this limit and show that sum rules up to the second moment, which requires the self-energy in the short wave length limit and zero frequency to be proportional to the kinetic energy per particle, are exactly satisfied. We compare our results with the impulse approximation and calculate the condensate fraction. An analytic expression for the momentum distribution is also derived.
A monofluid flow mathematical model of liquid helium II based on extended non-equilibrium thermodynamics
1994
The present work is a generalization of a previous analysis which aims at a single-fluid description of the macroscopic behaviour of helium II. A single-fluid model of helium II, with a wider range of temperatures and pressures than the one previously described, is formulated here using the extended thermodynamics of a non-ideal fluid in the absence of dissipation. The model here formulated includes, according to experimental data, the propagation of the two sounds typical of superfluid helium, a relationship between the stress deviator and the square of heat flux and an explanation of the fountain effect.
Non-classical Velocity Statistics in Counterflow Quantum Turbulence
2014
In this work we analyse the statistical distribution of turbulent superfluid velocity components in a He II counterflow channel, via two-dimensional numerical simulations pre- sented in past studies. The Probability Density Functions (PDFs) of the superfluid velocity components are investigated at lengthscales smaller than the average intervortex spacing, for varying vortex densities and different wall-normal distances. The results obtained con- firm the non-classical signature of quantum turbulence already observed in past numerical studies.
Waves Propagation in Superfluid Helium in Presence of Combined Rotation and Counterflow
2008
Using the linear macroscopic mono-fluid model of liquid helium II, in which the fundamental fields are the density ?, the velocity v, the temperature T and heat flux q and taking into account the expression of an additional pressure tensor P(w), introduced to describe phenomena linked to vortices, a complete study of wave propagation is made in the complex situation involving thermal counterflow in a rotating cylinder.