13,931 research outputs found
Anomalous transport in Charney-Hasegawa-Mima flows
Transport properties of particles evolving in a system governed by the
Charney-Hasegawa-Mima equation are investigated. Transport is found to be
anomalous with a non linear evolution of the second moments with time. The
origin of this anomaly is traced back to the presence of chaotic jets within
the flow. All characteristic transport exponents have a similar value around
, which is also the one found for simple point vortex flows in the
literature, indicating some kind of universality. Moreover the law
linking the trapping time exponent within jets to the transport
exponent is confirmed and an accumulation towards zero of the spectrum of
finite time Lyapunov exponent is observed. The localization of a jet is
performed, and its structure is analyzed. It is clearly shown that despite a
regular coarse grained picture of the jet, motion within the jet appears as
chaotic but chaos is bounded on successive small scales.Comment: revised versio
Turbulent Mixing in Transverse Jets
Turbulent mixing is studied in liquid-phase transverse jets.
Jet-fluid concentration fields were measured using laser-induced fluorescence and digital-imaging techniques, for jets in the Reynolds number range 1000 <= Re <= 20,000, at a jet-to-freestream velocity ratio of 10. Analysis of the measured scalar fields indicates that turbulent mixing is Reynolds-number dependent, as manifest in the evolving probability density functions of jet-fluid concentration.
Enhanced homogenization is found with increasing Reynolds number. Turbulent mixing is also seen to be flow dependent, based on differences between jets discharging into a crossflow and jets into a quiescent reservoir. A novel technique for whole-field measurement of scalar increments was used to study the distribution of difference (scalar increments) of the scalar field. These scalar increments are found to tend toward exponential-tailed distributions with decreasing separation distance. Finally, the scalar field is found to be anisotropic, particularly at small length scales. This is seen in power spectra, directional scalar microscales, and directional PDFs of scalar increments. The local anisotropy of the scalar field is explained in terms of the global dynamics and large-scale strain field of the transverse jet
Controlling turbulent drag across electrolytes using electric fields
Reversible in operando control of friction is an unsolved challenge crucial
to industrial tribology. Recent studies show that at low sliding velocities,
this control can be achieved by applying an electric field across electrolyte
lubricants. However, the phenomenology at high sliding velocities is yet
unknown. In this paper, we investigate the hydrodynamic friction across
electrolytes under shear beyond the transition to turbulence. We develop a
novel, highly parallelised, numerical method for solving the coupled
Navier-Stokes Poisson-Nernest-Planck equation. Our results show that turbulent
drag cannot be controlled across dilute electrolyte using static electric
fields alone. The limitations of the Poisson-Nernst-Planck formalism hints at
ways in which turbulent drag could be controlled using electric fields.Comment: Accepted by the Faraday Discussions on Chemical Physics of
Electroactive Material
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