Search results for "Turbulence"

Effective thermal conductivity of superuid helium: Laminar, turbulent and ballistic regimes

2016

Abstract In this paper we extend previous results on the effective thermal conductivity of liquid helium II in cylindrical channels to rectangular channels with high aspect ratio. The aim is to compare the results in the laminar regime, the turbulent regime and the ballistic regime, all of them obtained within a single mesoscopic formalism of heat transport, with heat flux as an independent variable.

Approches région et bayésienne pour la restauration ďimages dégradées par la turbulence atmosphérique

2001

La turbulence atmospherique perturbe ľobservation a haute resolution. C’est un phenomene etudie depuis longtemps, en astronomie notamment. Le present article porte sur le cas de ľobservation ďun objet situe environ vingt kilometres, la propagation etant horizontale et pres du sol, en infrarouge. Les images a longue pose sont restaurees avec des algorithmes classiques de deconvolution. Les resultats ne sont satisfaisants que pour une faible perturbation. Il est plus avantageux ďexploiter des images courte pose, car elles contiennent plus de hautes frequences spatiales; mais ľobjet observe y fluctue aleatoirement. On travaille donc ici partir ďune sequence de plusieurs dizaines ďimages. Deux …

Effect of the Converging Pipe on the Performance of a Lucid Spherical Rotor

2018

Lucid spherical rotor is a cross-flow rotor developed to be installed within a pipeline. The purpose of installing this type of rotor is to collect excess energy available in gravity-fed water pipelines. In order to enhance the efficiency of the rotor which is installed in a channel, this paper aims to study the performance of Lucid spherical rotor with converging pipe. Numerical investigations were carried out to analyze the effect of the converging pipe on the performance of the rotor. Numerical simulations have been carried out using the unsteady Reynolds-averaged Navier–Stokes equations in conjunction with the realizable $$k-{\varepsilon }$$ turbulence model. The validation of the numer…

Rateless codes mitigation technique in a turbulent indoor Free Space Optics link

2014

Free Space Optics (FSO) links are affected by several impairments and, among them, optical turbulence is the most important factor that can degrade the link quality. Due to the presence of this phenomenon, the signal irradiance detected by the receiver fluctuates, thus causing erasure errors and fading events. In this work, we present an indoor Free Space Optics link, in which several turbulence conditions are generated by using two heating elements. We show that the generated turbulence causes erasure errors and packet losses during the data transmission, and we also compare the statistical distribution of the samples with the theoretical models. Moreover, we demonstrate how the applicatio…

A mathematical description of glitches in neutron stars

2017

In a pulsar, there are gaps and difficulties in our knowledge of glitches, mainly because of the absence of information about the physics of the matter of the star. This has motivated several authors to suggest dynamical models that interpret most of the astronomical data. Many predictions are based on the assumption that the inner part is analogous to the structure of matter of superfluids. Here, we illustrate a new mathematical model, partially inspired by the dynamics of superfluid helium. We obtain two evolution equations for the angular velocities (of the crust and of superfluid), which are supported by another evolution equation for the average vortex line length per unit volume. This…

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.

Incoherent Soliton Turbulence in Nonlocal Nonlinear Media

2011

The long-term behavior of a modulationally unstable nonintegrable system is known to be characterized by the soliton turbulence self-organization process: It is thermodynamically advantageous for the system to generate a large-scale coherent soliton in order to reach the (‘‘most disordered’’) equilibrium state. We show that this universal process of self-organization breaks down in the presence of a highly nonlocal nonlinear response. A wave turbulence approach based on a Vlasov-like kinetic equation reveals the existence of an incoherent soliton turbulence process: It is advantageous for the system to self-organize into a large-scale, spatially localized, incoherent soliton structure.

Optical turbulence measurements and channel modeling of an indoor Free Space Optics link

2014

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.

Prediction of Swirling Flow in a Corrugated Channel

1991

Laminar and turbulent flow in a corrugated channel is simulated using HARWELL-FLOW3D. The channel represents a typical cell within a proposed design for the heat-transfer element of a rotary regenerator. Velocity vectors in planes perpendicular and parallel to the axis of a corrugation are visualised using Harwell’s graphics package, OUTPROC. Both programs were mn on Harwell’s Cray 2. The velocity vector plots show clear evidence of swirl, which is thought to be the mechanism responsible for the high rates of heat transfer in this type of heat-exchanger geometry. The swirl strength is shown to be a function of the channel geometry.