Regions Of Strong Turbulence Research Articles

Study on the Difference in Wavefront Distortion on Beams Caused by Wavelength Differences in the Strong Turbulence Region

Study on the Difference in Wavefront Distortion on Beams Caused by Wavelength Differences in the Strong Turbulence Region

Investigation of a Magnetic Reconnection Event with Extraordinarily High Particle Energization in Magnetotail Turbulence

Magnetic reconnection and plasma turbulence are ubiquitous and key processes in the Universe. These two processes are suggested to be intrinsically related: magnetic reconnection can develop turbulence, and, in turn, turbulence can influence or excite magnetic reconnection. In this study, we report a rare and unique electron diffusion region (EDR) observed by the Magnetospheric Multiscale mission in the Earth’s magnetotail with significantly enhanced energetic particle fluxes. The EDR is in a region of strong turbulence within which the plasma density is dramatically depleted. We present three salient features. (1) Despite the turbulence, the EDR behaves nearly the same as that in 2D quasi-planar reconnection; the observations suggest that magnetic reconnection continues for several minutes. (2) The observed reconnection electric field and inferred energy transport are exceptionally large. However, the aspect ratio of the EDR (one definition of reconnection rate) is fairly typical. Instead, extraordinarily large-amplitude Hall electric fields appear to enable the strong energy transport. (3) We hypothesize that the high-energy transport rate, density depletion, and the strong particle acceleration are related to a near-runaway effect, which is due to the combination of low-plasma-density inflow (from lobes) and possible positive feedback between turbulence and reconnection. The detailed study on this EDR gives insight into the interplay between reconnection and turbulence, and the possible near-runaway effect, which may play an important role in other particle acceleration in astrophysical plasma.

The explosion characteristics of the insulating oil under unconfined conditions and its damage assessment

With the application of ultra-high voltage (UHV) technology, a substantial amount of energy released from an internal arc fault in the transformer leads to the instantaneous decomposition of insulating oil into various flammable gases. This results in a rapid increase in internal pressure, making it highly probable for the transformer casing to rupture. Consequently, the insulating oil and its decomposition products disperse in the air, which in the presence of an ignition source, can trigger an explosive accident. To reveal the explosion characteristics of insulating oil, experiments and simulations are conducted under unconfined conditions. Besides, a quantitative explosion risk assessment is conducted. The results indicate that, at 20 ms, a high temperature and strong turbulence region appears at about 0.9 m from the center of the cloud and 0.7 m in height, and the combustible cloud is initiated near the region. The safety distances for humans free from the hazard of shock waves are 11.79 m, 13.74 m, and 21.63 m with the amount of insulating oil of 10 L, 15 L, and 20 L, respectively, and the safety distances for humans free from the hazard of thermal radiation are 21.2 m, 26.4 m, and 29.2 m respectively.

Secrecy analysis of a free-space laser communication system with a coherent main channel

Physical layer security of a free-space optical (FSO) communication link is investigated for certain eavesdropping scenarios in which the eavesdropper exploits the divergence of the transmitted laser beam, which is subject to atmospheric turbulence, to compromise the security of the transmission link. A solution for physical layer security in which the legitimate receiver is positioned to receive only the coherent component of the transmitted laser beam is proposed. The irradiance fluctuations are modeled with separate distributions for the coherent and non-coherent components of the transmitted beam, corresponding to the main channel and the eavesdropper’s channel, respectively. Complete secrecy analysis of this setup is presented, and closed form expressions of the probability of strictly positive secrecy capacity, average secrecy capacity, and secrecy outage probability are derived. The analytical results are verified by Monte-Carlo simulations. Secrecy performance for worst-case scenarios corresponding to an adversary with powerful resources to capture all of the leaked information is explored. Results are analyzed for different turbulence regimes, and it was found that secure communication is possible even in the region of strong turbulence.

Observation of Magnetic Reconnection in a Region of Strong Turbulence

We examine a rare and interesting observation of magnetic reconnection embedded in a large-scale region of strong turbulence in which magnetic field annihilation is energizing ions and electrons. The magnetic reconnection event is in Earth’s magnetotail and is associated with enhanced energetic particle fluxes indicating local particle acceleration. Despite substantial electric and magnetic field fluctuations throughout the surrounding, large-scale region, the ongoing magnetic reconnection has many similar properties to laminar, 2D magnetic reconnection including Hall electric fields, Hall magnetic fields, a thin electron current sheet, and ion and electron jets. Notably, the electron jet emerging from the electron diffusion region (EDR) appears to transport sufficient off-diagonal momentum to infer that off-diagonal electron stress can support the reconnection electric field in the EDR even in a turbulent environment. Although the electron jet appears to be briefly (∼1 s) deflected or possibly interrupted by an electromagnetic disturbance, the reconnection appears to otherwise continue for a long period (∼30 minutes) as evidenced by a persistent ion jet. This particular finding implies that the fundamental electron-scale processes inside of the EDR in turbulent magnetic reconnection are not necessarily distinct from those in laminar magnetic reconnection. These observations provide direct confirmation that magnetic reconnection can not only be responsible for but also can continue in regions of large-scale turbulence. Because the electric and magnetic fields of strong turbulence are linked to particle acceleration, it follows that particle acceleration also can continue as a consequence of turbulent magnetic reconnection.

The effect of aggregation/disaggregation on suspended particulate matter transport in a tidal strait

Predicting net suspended sediment fluxes in coastal regions is important for promoting good water quality, maritime transport and marine industries. Aggregation and disaggregation of suspended particulate matter responding to spatial and temporal variations in turbulence can control particle size and hence settling speed; little is currently known about how this influences the net suspended sediment flux. A tidal strait, in which the flux is confined to be in one of two directions, makes a good site for observing the effect of changes in particle size on the suspended sediment flux. The Menai Strait in North Wales is a narrow tidal strait in which the flow speeds increase to a maximum in the narrowest central region, the Swellies. Observations at sites on either side of the Swellies show that the median size of suspended particles varies with the speed of the tidal current, but also depends on the direction of the flow, with the smallest particles seen when the current is flowing out of the Swellies. The implication (supported by model results) is that the strong currents in the centre of the strait tear up flocs into small pieces which are then carried out towards both ends of the strait by the tide. Averaged over a tidal cycle, there is a net flux of larger particles into the Swellies and a net flux of small particles out. These results are relevant to the formation of isolated turbidity maxima around a region of strong turbulence.

Energetic ions in the Venusian system: Insights from the first Solar Orbiter flyby

The Solar Orbiter flyby of Venus on 27 December 2020 allowed for an opportunity to measure the suprathermal to energetic ions in the Venusian system over a large range of radial distances to better understand the acceleration processes within the system and provide a characterization of galactic cosmic rays near the planet. Bursty suprathermal ion enhancements (up to ∼10 keV) were observed as far as ∼50RVdowntail. These enhancements are likely related to a combination of acceleration mechanisms in regions of strong turbulence, current sheet crossings, and boundary layer crossings, with a possible instance of ion heating due to ion cyclotron waves within the Venusian tail. Upstream of the planet, suprathermal ions are observed that might be related to pick-up acceleration of photoionized exospheric populations as far as 5RVupstream in the solar wind as has been observed before by missions such as Pioneer Venus Orbiter and Venus Express. Near the closest approach of Solar Orbiter, the Galactic cosmic ray (GCR) count rate was observed to decrease by approximately 5 percent, which is consistent with the amount of sky obscured by the planet, suggesting a negligible abundance of GCR albedo particles at over 2RV. Along with modulation of the GCR population very close to Venus, the Solar Orbiter observations show that the Venusian system, even far from the planet, can be an effective accelerator of ions up to ∼30 keV. This paper is part of a series of the first papers from the Solar Orbiter Venus flyby.

Spiral Spectrum of a Laguerre-Gaussian Beam Propagating in Anisotropic Turbulent Plasma

The explicit expression of orbital angular momentum (OAM) spiral spectrum of Laguerre-Gaussian (LG) beam propagating in anisotropic plasma turbulence is derived based on Rytov theory. The relationship between the detection probability of OAM and the crosstalk with the anisotropy parameters, topological charge, radial index, wavelength, beam width, receiving aperture, inner and outer scales are discussed in detail. In order to quantify the effect of plasma turbulence, we compared it with atmospheric turbulence based on restriction function. To optimize OAM detection probability, we also compared the effects of circular aperture method (CAM) with focusing mirror method (FMM) on the propagation characteristics of the spiral spectrum. The results show that even in the strong turbulence region of atmospheric turbulence, the radial dimension of LG beam in plasma turbulence is nearly twice that of atmospheric turbulence and the modes crosstalk has almost reached its upper bound. Besides, by comparing the two optimization methods, we found the ability to reduce crosstalk is related to the choice of beam width and receiving aperture. Therefore, we give a method to optimally select between the CAM and the FMM. We found the corresponding relationship and gave an analytical formula. The FMM has a greater ability to reduce crosstalk than the CAM when the beam width ≥4 cm and the aperture ≥3 cm. We quantified the effect of plasma turbulence and provide a guideline for the selection of beam width and receiving aperture under these two optimization methods. The research results may be helpful in the field of optical communication.

Best Practices for Comparing Ocean Turbulence Measurements across Spatiotemporal Scales

AbstractThe turbulent energy dissipation rate in the ocean can be measured by using rapidly sampling microstructure shear probes, or by applying a finescale parameterization to coarser-resolution density and/or shear profiles. The two techniques require measurements that are on different spatiotemporal scales and generate dissipation rate estimates that also differ in spatiotemporal scale. Since the distribution of the measured energy dissipation rate is closer to lognormal than normal and fluctuates with the strength of the turbulence, averaging the two approaches on equivalent spatiotemporal scales is critical for accurately comparing the two methods. Here, microstructure data from the 1997 Brazil Basin Tracer Release Experiment (BBTRE) is used to demonstrate that comparing averages of the dissipation rate on different spatiotemporal scales can generate spurious discrepancies of up to a factor of order 10 in regions of strong turbulence and smaller biases of up to a factor of 2 in the presence of weaker turbulence.

Observations of Particle Acceleration in Magnetic Reconnection–driven Turbulence

Abstract The Magnetospheric Multiscale Mission observes, in detail, charged particle heating and substantial nonthermal acceleration in a region of strong turbulence ( , where is the magnetic field) that surrounds a magnetic reconnection X-line. Magnetic reconnection enables magnetic field annihilation in a volume that far exceeds that of the diffusion region. The formidable magnetic field annihilation breaks into strong, intermittent turbulence with magnetic field energy as the driver. The strong, intermittent turbulence appears to generate the necessary conditions for nonthermal acceleration. It creates intense, localized currents ( ) and unusually large-amplitude electric fields ( ). The combination of turbulence-generated and results in a significant net positive mean of , which signifies particle energization. Ion and electron heating rates are such that they experience a fourfold increase from their initial temperature. Importantly, the strong turbulence also generates magnetic holes or depletions in that can trap particles. Trapping considerably increases the dwell time of a subset of particles in the turbulent region, which results in significant nonthermal particle acceleration. The direct observation of strong turbulence that is enabled by magnetic reconnection with nonthermal particle acceleration has far-reaching implications, since turbulence in plasmas is pervasive and may occupy significant volumes of the interstellar medium and intergalactic space. For example, strong turbulence from magnetic field annihilation in the supernova nebulae may dominate large volumes. As such, this observed energization process could plausibly contribute to the supply and development of the cosmic-ray spectrum.

Particle Acceleration in Strong Turbulence in the Earth’s Magnetotail

Abstract In many space, astrophysical, and laboratory plasmas the energy contained in the magnetic field or plasma flow exceeds the thermal energy. Magnetic field ( ) annihilation, often enabled by magnetic reconnection, transfers magnetic energy to particles. Shocks transfer bulk flow energy to particles. If there is a sufficiently large energy transfer, strong turbulence (∣ ∣/∣ B ∣ ∼ 1) develops, which, in turn, can result in nonthermal acceleration. In this article, we investigate acceleration in a finite-sized region of strong turbulence driven by magnetic reconnection with analytical modeling and test-particle simulations. This research is based on detailed observations in the Earth’s magnetotail. We find that the primary transfer of magnetic energy to particle energy is advanced by large-amplitude electric field structures ( ) generated by the strong turbulence. To no surprise, ion energization is dominated by intense DC , near the ion cyclotron frequency (f ci ), and/or variations at scales near the ion gyroradius. Electron energization comes from higher-frequency . The turbulent cascade continuously regenerates near f ci and higher frequencies. Importantly, the turbulence also creates magnetic depletions that can trap particles and considerably increase their dwell time in regions of strong energization, which substantially enhances nonthermal acceleration. Moreover, energization is primarily perpendicular to , so particles have difficulty escaping regions of depleted , which can lead to near runaway acceleration. We discuss how this process may be active in large-scale settings such as supernova shells and may contribute, at least in in part, to the development of the cosmic ray spectrum.

Estimation of scintillation and bit error rate performance of sine hollow beam via random phase screen

We study scintillation and bit error rate performance of sine hollow beam in turbulent atmosphere. Since source field expression involves higher order term, we model atmosphere utilizing random phase screen. We show that normal sine hollow beam (a=b) having higher order has the least scintillation index considering point like scintillation. This brings us bit error rate(BER) of this type of beam in turbulent atmosphere is less comparing with Gauss beam when we use point like receiver. BER of anomalous beam (a≠b) having less scintillation index is lower than Gauss beam in strong turbulence region. In terms of aperture averaged scintillation, first order normal sine hollow beam and anomalous beams have less scintillation than Gauss beam.

Spectrum in the Strong Turbulence Region of Gross–Pitaevskii Turbulence

Numerical simulations of the Gross–Pitaevskii equation which describes the dynamics of quantum fluids are performed focusing on scales larger than the healing length. Dissipation and pumping of the mass are applied in high and low wavenumber ranges, respectively, in order to achieve turbulent states. In this setting of dissipation and pumping, it is found that the mass, or the particle number, cascades from low to high wavenumbers and a constant flux of the particle number is observed in the cascading wavenumber range. The spectrum F(k) (k is the wavenumber) of the order parameter field at the turbulent state is analyzed, and it is found that the obtained F(k) is consistent with the form $$\propto k^{-1}[\ln (k/k_0)]^{-1}$$ ( $$k_0$$ is the lower-end wavenumber of the scaling range) which is derived from a closure approximation of the particle-number transfer range of strong turbulence (Yoshida and Arimitsu in J Phys A Math Theor 46(33):335501, 2013).

対向流燃焼を適用したストーカ式焼却炉の低NOx化に関する性能評価

JFE Engineering has developed the advanced stoker-type incineration system “JFE Hyper 21 Stoker System”, which adopts high temperature air combustion technology. With this technology, the incinerator realizes stable combustion in the condition of low excess air ratio, which results in reduction of NOx formation. In this paper, we describe a newly developed stoker-type incinerator which utilizes counter flow combustion in addition to high temperature air combustion technology. Verification experiment was conducted and further reduction of NOx formation was achieved. Experiment and numerical simulation were carried out to consider the reduction mechanism of NOx. Flat combustion region which contributes to stable combustion was observed in both experiment and simulation. Oxygen concentration distribution in the furnace implies that effective two-staged combustion is formed. From the view of fluid analysis, strong turbulence region is formed in the downstream of the furnace. These factors are considered to interact with each other and contribute to suppress the NOx formation.

Scintillation behaviour of vortex beams in strong turbulence region

We study the scintillation behaviour of vectorial vortex beams in strong turbulence region. For this purpose, a list of vortex source beams is prepared. Then their scintillation performances are analysed one by one using the random phase screen approach. The results indicate that there will always be scintillation reductions with increasing values of topological charge, although its effect will diminish as we go towards higher values of the topological charge. The increases in the other specific beam parameters seem to have opposite effect. For the vectorial Hermite Gaussian beam, the use of higher orders will also aid scintillation reductions. It is foreseen that the outcome of this study will be useful for long haul optical communication links.

A frequency domain linearized Navier–Stokes method including acoustic damping by eddy viscosity using RANS

In this paper, a method for including damping of acoustic energy in regions of strong turbulence is derived for a linearized Navier–Stokes method in the frequency domain. The proposed method is validated and analyzed in 2D only, although the formulation is fully presented in 3D. The result is applied in a study of the linear interaction between the acoustic and the hydrodynamic field in a 2D T-junction, subject to grazing flow at Mach 0.1. Part of the acoustic energy at the upstream edge of the junction is shed as harmonically oscillating disturbances, which are conveyed across the shear layer over the junction, where they interact with the acoustic field. As the acoustic waves travel in regions of strong shear, there is a need to include the interaction between the background turbulence and the acoustic field. For this purpose, the oscillation of the background turbulence Reynold׳s stress, due to the acoustic field, is modeled using an eddy Newtonian model assumption. The time averaged flow is first solved for using RANS along with a k-ε turbulence model. The spatially varying turbulent eddy viscosity is then added to the spatially invariant kinematic viscosity in the acoustic set of equations. The response of the 2D T-junction to an incident acoustic field is analyzed via a plane wave scattering matrix model, and the result is compared to experimental data for a T-junction of rectangular ducts. A strong improvement in the agreement between calculation and experimental data is found when the modification proposed in this paper is implemented. Discrepancies remaining are likely due to inaccuracies in the selected turbulence model, which is known to produce large errors e.g. for flows with significant rotation, which the grazing flow across the T-junction certainly is. A natural next step is therefore to test the proposed methodology together with more sophisticated turbulence models.

Sheared stably stratified turbulence and large-scale waves in a lid driven cavity

We investigated experimentally stably stratified turbulent flows in a lid driven cavity with a non-zero vertical mean temperature gradient in order to identify the parameters governing the mean and turbulent flows and to understand their effects on the momentum and heat transfer. We found that the mean velocity patterns (e.g., the form and the sizes of the large-scale circulations) depend strongly on the degree of the temperature stratification. In the case of strong stable stratification, the strong turbulence region is located in the vicinity of the main large-scale circulation. We detected the large-scale nonlinear oscillations in the case of strong stable stratification which can be interpreted as nonlinear internal gravity waves. The ratio of the main energy-containing frequencies of these waves in velocity and temperature fields in the nonlinear stage is about 2. The amplitude of the waves increases in the region of weak turbulence (near the bottom wall of the cavity), whereby the vertical mean temperature gradient increases.

Average capacity for optical wireless communication systems over exponentiated Weibull distribution non-Kolmogorov turbulent channels.

We model the average channel capacity of optical wireless communication systems for cases of weak to strong turbulence channels, using the exponentiation Weibull distribution model. The joint effects of the beam wander and spread, pointing errors, atmospheric attenuation, and the spectral index of non-Kolmogorov turbulence on system performance are included. Our results show that the average capacity decreases steeply as the propagation length L changes from 0 to 200m and decreases slowly down or tends to a stable value as the propagation length L is greater than 200m. In the weak turbulence region, by increasing the detection aperture, we can improve the average channel capacity and the atmospheric visibility as an important issue affecting the average channel capacity. In the strong turbulence region, the increase of the radius of the detection aperture cannot reduce the effects of the atmospheric turbulence on the average channel capacity, and the effect of atmospheric visibility on the channel information capacity can be ignored. The effect of the spectral power exponent on the average channel capacity in the strong turbulence region is higher than weak turbulence region. Irrespective of the details determining the turbulent channel, we can say that pointing errors have a significant effect on the average channel capacity of optical wireless communication systems in turbulence channels.

Melting dynamics of large ice balls in a turbulent swirling flow

We study the melting dynamics of large ice balls in a turbulent von Kármán flow at very high Reynolds number. Using an optical shadowgraphy setup, we record the time evolution of particle sizes. We study the heat transfer as a function of the particle scale Reynolds number \documentclass[12pt]{minimal}\begin{document}$\mbox{\textit {Re}}_{D}$\end{document}ReD for three cases: fixed ice balls melting in a region of strong turbulence with zero mean flow, fixed ice balls melting under the action of a strong mean flow with lower fluctuations, and ice balls freely advected in the whole apparatus. For the fixed particles cases, heat transfer is observed to be much stronger than in laminar flows, the Nusselt number behaving as a power law of the Reynolds number: \documentclass[12pt]{minimal}\begin{document}$\mbox{\textit {Nu}} \propto \mbox{\textit {Re}}_{D}^{0.8}$\end{document}Nu∝ReD0.8. For freely advected ice balls, the turbulent transfer is further enhanced and the Nusselt number is proportional to the Reynolds number \documentclass[12pt]{minimal}\begin{document}$\mbox{\textit {Nu}} \propto \mbox{\textit {Re}}_{D}$\end{document}Nu∝ReD. Furthermore, the surface heat flux is found to be independent of the particles size, leading to an ultimate regime of heat transfer reached when the thermal boundary layer is fully turbulent.

Distribution of turbulent plasma in the galaxy

It is shown that the level of plasma turbulence strongly depends on a direction in the Galaxy. It is obtained that there are nearly three orders of magnitude larger in the directions of the central portions of the Galaxy at low latitudes IbI 10°. In the galactic arms the highest values of level of turbulence are near supernova remnants located in the regions with large electron densities. We show that the typical radius of the strong turbulence region around supernova remnants is ≅ 35 pc. Within this region the level of plasma turbulence is approximately 10 times larger, than on its edges. It is concluded that presence of supernova explosions in the medium with large density is necessary for existence of strong turbulence in interstellar plasma.