arXiv subjects

A. Bershadskii

Publications and source records attributed to A. Bershadskii.

At least 37 records · Page 2Linked to original sources

arXiv2021

MHD dynamo in swirling turbulence: from deterministic to helical distributed chaos

Using results of laboratory experiments, direct numerical simulations, geomagnetic and solar observations, it is shown that high moments of helicity distribution can dominate power spectra of the magnetic field generated by the magnetohydrodynamic (MHD) dynamo in swirling turbulence even for the cases with zero global helicity. The notion of helical distributed chaos has been used for this purpose.

physics.flu-dyn↗

arXiv2021

Helical distributed chaos in rotating turbulence and convection (with applications to geomagnetic dynamo)

The role of the moments of helicity distribution in rotating turbulence has been studied using the notion of helical distributed chaos. Results of the direct numerical simulations, laboratory experiments and geophysical observations have been used in this investigation. It is shown, in particular, that even for the cases when the global helicity is equal to zero at least even moments are usually non-zero (due to the appearance of the local spatial regions with strong negative and positive helicity) and can play a significant role in the rotating turbulence as adiabatic invariants. Rotating buoyancy driven thermal convection (Rayleigh-Bénard and Rayleigh-Taylor, the former also for the magnetohydrodynamics) is also studied, and applications of this approach to the convection zone of massive stars and to the geomagnetic dynamo have been discussed in this context.

physics.flu-dyn↗

arXiv2021

Cross-helicity and transition from magnetohydrodynamics to kinetics in space plasmas

Cross-helicity dominated distributed chaos (CHDC) for magnetohydrodynamic (large-scale) and kinetic (small-scale) ranges of space plasmas has been studied using results of direct numerical simulations and of measurements made in the Earth's magnetosheath and in free solar wind by the instruments onboard of the Magnetospheric Multiscale Mission and CLUSTER spacecrafts. Existence of two generic types of transition from the magnetohydrodynamic (MHD) to kinetic range has been shown: 1) from the Kolmogorov-like (scaling) MHD turbulence to the kinetic CHDC and 2) from the magnetohydrodynamic CHDC to the kinetic CHDC. Results of measurements in the magnetosheath of some other planets: Saturn (Cassini observations), Jupiter (Galileo observations), and Mercury (Messenger observations), have been briefly discussed in this contest.

physics.space-ph↗

arXiv2021

Helicity, low-dimensional distributed chaos and scaling in MHD turbulence

It is shown that the second-order moment of helicity distribution (the Levich-Tsinober invariant of inviscid hydrodynamics) can be preserved as an adiabatic invariant in magnetohydrodynamics. The distributed chaos approach and inertial range phenomenology have been developed for the magnetohydrodynamic processes dominated by this adiabatic invariant, and some consequences of the theoretical consideration have been compared with results of direct numerical simulations and measurements in the solar wind. Helical scaling in interstellar MHD turbulence has been also briefly discussed in this context.

physics.flu-dyn↗

arXiv2021

Passive scalar tracers in chaotic and turbulent atmosphere

The notion of helical distributed chaos has been used for the description of the spatio-temporal dynamics of the passive scalar tracers from the atmospheric surface layer up to the mesosphere (at different stability conditions and different latitudes). Point, linear and distributed sources and sinks with different types of artificial and natural trace-gases (ozone, carbon dioxide, etc.), and aerosols have been studied. Related properties of the solar radiation transmittance in the cloudy atmosphere have been also briefly discussed as well as analogous properties of the tracers in Jupiter's atmosphere.

physics.ao-ph↗

arXiv2021

Chaos and turbulence in clouds

Spatial buoyancy-helical distributed chaos (turbulence) in the cumulus, stratiform, stratocumulus, cirrus and cirrus mammatus clouds have been studied using results of direct numerical simulations and measurements in cloudy atmosphere. It is shown that in the considered cases the moments of helicity distribution dominate the kinetic energy spectra both in the middle of the clouds and in the cloud-top regions.

physics.ao-ph↗

arXiv2020

Chaotic and turbulent temperature fluctuations in atmospheric free convection

It is shown, using results of direct numerical simulations, laboratory experiments, measurements in the atmospheric boundary layer, satellite infrared radiances data, the planetary-scale surface-air and tropospheric data, that the temperature fluctuations in atmospheric free convection can be well described by the spatio-temporal distributed chaos approach based on the Bolgiano-Obukhov phenomenology. A possibility of analogous consideration of the atmospheric dynamics on other planets (Mars, Jupiter and Saturn) has been briefly discussed using the data obtained with the Phoenix lander and the infrared observations.

physics.ao-ph↗

arXiv2020

Dissipative invariants in MHD turbulence

Role of the dissipative invariants in isotropic homogeneous MHD turbulence has been studied using the distributed chaos approach and results of direct numerical simulations. Effects of weak imposed mean magnetic field and magnetic fields in undisturbed solar photosphere are also briefly discussed in this context.

physics.flu-dyn↗

arXiv2020

Helical velocity fluctuations and large-scale circulation in turbulent thermal convection

It is shown that helicity dynamics dominates spectral distribution of the velocity fluctuations in turbulent thermal convection at moderate and large values of the Rayleigh number (distributed chaos and scaling respectively). The large-scale circulation (wind) in the turbulent Rayleigh-Bénard convection is especially sensitive to the helicity dynamics and its chaotic reversals can be associated with the reversals of the mean helicity sign (the ergodic restoration of the reflectional symmetry in a long run). Results of the laboratory experiments and measurements in the free atmospheric convection have been used in order to support the theoretical considerations based on the adiabatic invariance of the second order moment of the helicity distribution. The geomagnetic field dipole variability and reversals have been also discussed in this context and good agreement with results of numerical simulations and observational data has been established.

physics.flu-dyn↗

arXiv2020

Strong chaotic fluctuations of laser beams propagating through temperature inhomogeneities in the atmosphere

The atmospheric temperature inhomogeneities are the main cause of the index of refraction variations resulting in strong fluctuations of intensity of the laser beams propagating through the atmosphere. It is shown that the Kolmogorov-Bolgiano-Obukhov phenomenology of the thermal (buoyancy driven) convection can effectively describe this process in the frames of the distributed chaos approach. Results of the direct numerical simulations and measurements in the urban atmosphere (based on the laser beams with the wavelengths of 532nm and 690nm) have been used in order to support the theoretical considerations.

physics.ao-ph↗

arXiv2019

Multiplicity of chaotic and turbulent regimes in Rayleigh-Bénard convection

Multiple chaotic and turbulent regimes in Rayleigh-Bénard convection have been studied and classified from the onset of deterministic chaos to the fully developed turbulence using the distributed chaos approach supported by results of laboratory experiments and numerical simulations. It is shown that the regimes can replace each other depending on value of the Rayleigh number and location in the convection cell (in the bulk of the flow or in the boundary layers). The inertial-buoyancy and helicity based invariants play crucial role in the formation of the regimes. Transition from the classical to ultimate state has been also discussed in this context.

physics.flu-dyn↗

arXiv2019

Cross-helicity and extended inertial range in MHD turbulence

An extended inertial range dominated by the cross-helicity effects has been studied for forced (statistically steady) and for freely decaying magnetohydrodynamic MHD turbulence (with and without imposed/mean magnetic field) using the spatio-temporal distributed chaos approach. Good agreement with results of direct numerical simulations, laboratory measurements in MHD wind (plasma) tunnel, measurements in the Earth's magnetosheath and in the solar wind has been established. A spontaneous breaking of local reflection (mirror) symmetry has been briefly discussed for the MHD turbulence with zero average cross-helicity.

physics.flu-dyn↗

arXiv2019

Role of correlation integrals in helical isotropic turbulence

It is shown that the correlation integrals (invariants) play an important, and at certain conditions a dominant, role in helical isotropic homogeneous turbulence both in the inertial and near-dissipation ranges. Results of direct numerical simulations and recent laboratory experiments with multiscale grids have been used for this purpose. A possibility of spontaneous breaking of reflection symmetry has been also briefly discussed in this context.

physics.flu-dyn↗

arXiv2019

Helical distributed chaos in magnetic field of solar wind

Helical distributed chaos in magnetic field has been studied using results of direct numerical simulations (dominated by magnetic helicity), of a laboratory experiment with plasma wind tunnel and of solar wind measurements (dominated by combined magnetic and cross helicity effects). The solar wind measurements, used for the spectral computations, were produced by Helios-1 and Ulysses missions for low and high heliolatitudes respectively and for high solar wind speed at $0.4 < R <4.5$ AU (where $R$ is distance from the Sun).

physics.space-ph↗

arXiv2019

Chaotic and turbulent dispersion of heavy inertial particles

Chaotic and turbulent dispersion of passive heavy inertial particles in homogeneous two-dimensional turbulence with Ekman drag has been studied using notions of the effective diffusivity and distributed chaos. Results of recent direct numerical simulations have been used for this purpose. Effect of the Stokes number value on the applicability of these notions to the dispersion of passive heavy inertial particles has been briefly discussed.

physics.flu-dyn↗

arXiv2019

Eelectrokinetic turbulence and chaos in ionic migration and in microfluidic convection

Turbulence in the ionic migration and in the microfluidic electro-hydrodynamic convection (mixing) under constant and low-frequency external electric field has been studied using distributed chaos approach and notion of effective (turbulent) diffusivity. Results of corresponding laboratory experiments have been also used for this purpose. It is shown that for the migration and convection (mixing) under constant and low-frequency external electric field the turbulent power spectra have stretched exponential form $E(k) \propto \exp-(k/k_β)^{2/3}$. In the case of the microfluidic convection the distributed chaos is tuned to the large-scale coherent structures generated by the low-frequency oscillating external electric field ( $k_β$ is proportional to the forcing frequency).

physics.flu-dyn↗

arXiv2019

Lagrangian chaos and turbulent diffusivity

Passive scalar mixing, produced by Lagrangian chaos generated a) by quasi-periodic (integrable) motion of three quasi-point vortices and b) by chaotic motion of three and six quasi-point vortices, has been studied and compared with turbulent mixing of passive scalar in 2D and 3D steady isotropic homogeneous turbulence and in turbulent wakes behind grid and behind cylinder. Results of numerical and laboratory experiments have been used and effective diffusivity approximation as well as distributed chaos approach have been applied to this problem.

physics.flu-dyn↗

arXiv2019

Chaotic and turbulent mixing of passive scalar

Spatio-temporal deterministic chaos at small Taylor-Reynolds numbers $Re_λ \lesssim 40$ and distributed chaos at turbulent $Re_λ \gtrsim 40$ in passive scalar dynamics have been studied using results of direct numerical simulations of homogeneous incompressible flows (with and without mean gradient of the passive scalar) for $8 \leq Re_λ < 700$ and of a reacting turbulent mixing layer. It is shown that the deterministic chaos in the passive scalar fluctuations at the small $Re_λ$ is characterized by exponential spatial (wavenumber) spectrum: $E(k) \propto \exp-(k/k_c)$, whereas the distributed chaos at turbulent $Re_λ$ is characterized by stretched exponential spectrum $E(k) \propto \exp-(k/k_β)^{3/4}$. The Birkhoff-Saffman invariant related to the momentum conservation and, due to the Noether theorem, to the spatial homogeneity has been used as a theoretical basis for this stretched exponential spectrum. Although the $k_c$ and $k_β$ represent the large-scale structures a relevance of the Batchelor scale $k_{bat}$ has been established as well: the normalized values $k_c/k_{bat}$ and $k_β/k_{bat}$ exhibit universality.

physics.flu-dyn↗