451,153 research outputs found
Kolmogorov Spectrum of Quantum Turbulence
There is a growing interest in the relation between classical turbulence and
quantum turbulence. Classical turbulence arises from complicated dynamics of
eddies in a classical fluid. In contrast, quantum turbulence consists of a
tangle of stable topological defects called quantized vortices, and thus
quantum turbulence provides a simpler prototype of turbulence than classical
turbulence. In this paper, we investigate the dynamics and statistics of
quantized vortices in quantum turbulence by numerically solving a modified
Gross-Pitaevskii equation. First, to make decaying turbulence, we introduce a
dissipation term that works only at scales below the healing length. Second, to
obtain steady turbulence through the balance between injection and decay, we
add energy injection at large scales. The energy spectrum is quantitatively
consistent with the Kolmogorov law in both decaying and steady turbulence.
Consequently, this is the first study that confirms the inertial range of
quantum turbulence.Comment: 14pages, 24 figures and 1 table. Appeared in Journal of the Physical
Society of Japan, Vol.74, No.12, p.3248-325
Study of the atmospheric turbulence in free space optical communications
Abstract-In this paper the effect of atmospheric turbulence on free space optical (FSO) communications is investigated experimentally by designing a turbulence simulation chamber. The distributions of bits â0 â and â1 â levels are measured with and without turbulence. The bit error rate (BER) is then obtained from the distributions. The temperature gradient within the channel is less than 6 °C resulting in turbulence of log irradiance variance of 0.002. The received average signal is measured and used to characterise the simulated turbulence strength. We then evaluated the BER with turbulence and found that from an error free link in the absence of turbulence, the BER increased significantly to about 10-4 due to the turbulence effect. I
A stability condition for turbulence model: From EMMS model to EMMS-based turbulence model
The closure problem of turbulence is still a challenging issue in turbulence
modeling. In this work, a stability condition is used to close turbulence.
Specifically, we regard single-phase flow as a mixture of turbulent and
non-turbulent fluids, separating the structure of turbulence. Subsequently,
according to the picture of the turbulent eddy cascade, the energy contained in
turbulent flow is decomposed into different parts and then quantified. A
turbulence stability condition, similar to the principle of the
energy-minimization multi-scale (EMMS) model for gas-solid systems, is
formulated to close the dynamic constraint equations of turbulence, allowing
the heterogeneous structural parameters of turbulence to be optimized. We call
this model the `EMMS-based turbulence model', and use it to construct the
corresponding turbulent viscosity coefficient. To validate the EMMS-based
turbulence model, it is used to simulate two classical benchmark problems,
lid-driven cavity flow and turbulent flow with forced convection in an empty
room. The numerical results show that the EMMS-based turbulence model improves
the accuracy of turbulence modeling due to it considers the principle of
compromise in competition between viscosity and inertia.Comment: 26 pages, 13 figures, 2 table
Recent Developments in Understanding Two-dimensional Turbulence and the Nastrom-Gage Spectrum
Two-dimensional turbulence appears to be a more formidable problem than
three-dimensional turbulence despite the numerical advantage of working with
one less dimension. In the present paper we review recent numerical
investigations of the phenomenology of two-dimensional turbulence as well as
recent theoretical breakthroughs by various leading researchers. We also review
efforts to reconcile the observed energy spectrum of the atmosphere (the
spectrum) with the predictions of two-dimensional turbulence and
quasi-geostrophic turbulence.Comment: Invited review; accepted by J. Low Temp. Phys.; Proceedings for
Warwick Turbulence Symposium Workshop on Universal features in turbulence:
from quantum to cosmological scales, 200
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