The fundamental possibility of studying the process of additional generation of turbulence in flows with large particles is demonstrated with a model based on the system of Reynolds-averaged Navier–Stokes (RANS) equations. Calculations of additional generation of turbulence in an ascending air flow with large particles were performed. The calculation results are compared with the available experimental data, taking into account the actual values of the mass concentration of particles.

This paper presents the results of measurements of the solid particle concentration field near a frontal point of a cylindrical body with a flat end. We restore the particle concentration fields based on their image identification obtained by photographic fixation at low shutter speeds. The experiments revealed the effect of increasing the particle concentration near the body surface, which appears more clearly with the increase in the local particle concentration in the oncoming flow. We analyze the mechanisms of the particle concentration increase in the flow around bodies by flows containing particles.

The characteristics of a flow formed behind a large particle moving in a descending turbulent air flow in a duct was measured using the PIV method, which makes it possible to record the instantaneous velocity fields. Data on deformation of the field of the instantaneous air velocity in a turbulent wake behind a large particle are presented and analyzed.

It is shown that a diamagnetic structure (DS) of the slow solar wind (SW), the source of which on the Sun was a chain of streamers, arrived at Earth’s orbit on December 22, 2015. It interacted with Earth’s magnetosphere under conditions when the northward Bz component of the interplanetary magnetic field (IMF) remained for a long time in preceding undisturbed SW. The interaction and a sharp change in the direction of Bz to the south generated an isolated substorm whose duration depends on the duration of interaction with the DS. The substorm began at midday with the passage of the DS into the magnetosphere and spread to the east. All phases of the substorm — growth, expansion, and recovery — were observed for two hours. Variations in the SW and IMF parameters are shown to coincide for the isolated substorm whose energy source was the slow solar wind DS, and a trigger was the abrupt change in the direction of the vertical IMF component from north to south. The coincidence is justified by statistical generalizations of the same parameters in 40 % of cases of long-term observations of individual substorms whose trigger was a change in Bz direction.

Measurement of the fields of particle concentration is one of the main task in research area of the two-phase flows around bodies in 'gas -solid particles' case.The paper considers the reconstruction of the concentration fields of solid particles by identifying their images.An experimental setup scheme for analysis of the structure of downward two-phase flow is presented.The main parameters of the experimental setup are as follows: geometry of the working area, air flow velocity, air flow rate, mass flow rate of particles.An optical monochrome setup for recording fast processes is briefly described.A method for processing experimental images based on the Canny edge detector is proposed.The processing algorithm for the experimental images was tested on glass microspheres used as a dispersed phase.The original image and a size distribution histogram for microstructures are presented.Examples of individual images of microspheres in a flow are considered for data validation.The experimental determination of the particle concentration fields in the downward flow and in the vicinity of the streamlined body are presented.

Показано, что на орбите Земли 22.12.2015 г. взаимодействие диамагнитной структуры (ДС) медленного солнечного ветра с магнитосферой после продолжительной северной ориентации Bz генерирует изолированную суббурю, длительность которой определяется длительностью ДС. Суббуря начинается в околополуденные часы прохождением ДС в магнитосферу и распространяется к востоку. В течение двух часов наблюдаются все фазы суббури – подготовительная, взрывная и восстановительная. Протоны ДС, генерируясь в области источника, достигают орбиты Земли и, взаимодействуя с частицами радиационных поясов, вызывают генерацию колебаний IPDP в околополуденные часы в большом широтном диапазоне.

The study of free non-stationary vortex structures by the PIV method requires the search for the most rational approach to visual data processing.The paper evaluates the qualitative and quantitative characteristics of the velocity fields based on the generator of random synthetic particles.The simplified case of a solid-state rotation with a given velocity is considered as the closest to the vortex motion.

In this work, our discovery for the first time of a two-spiral nonstationary structure of interacting vortex filaments preceding the generation of a wall-free nonstationary air vortex is described.

We consider aspects of using the method of anemometry on particle images to measure the velocity fields of nonstationary air vortices. To prevent the loss of a cross-pair when a particle passes through a light curtain, a method is proposed for determining the time delay between frames. Methods for measuring the velocity fields of nonstationary air vortices are described taking into account the vertical velocity of particles when the actual velocity is reproduced from the measured horizontal projection in the case of using a two-dimensional (single-chamber) type of anemometry method.

This paper is aimed to demonstrate an opportunity of the generation of nonstationary wall-free fire whirls under laboratory conditions without using mechanical swirling devices and to estimate their integral parameters. A simple experimental facility, making possible the generation of concentrated fire vortex structures by means of combustion of solid fuel (urotropine) arranged symmetrically on a metallic underlying surface, is described. With the use of photography, some novel data on the probability of generation of fire whirls depending on the experimental mode have been obtained.

In this work, for the first time, a double spiral non-stationary structure of interacting helical filaments, preceding the generation of a non-stationary air vortex, was discovered and described.

Using the June 22, 2015 event as an example, we present new data confirming the presence of a precursor of the sudden magnetic impulse caused by a powerful interplanetary shock wave (ISW). The precursor in the form of a train of oscillations (broadband pulse) with a falling frequency in the range 0.25÷11 Hz with a duration of ~20 s, which had a spectral resonance structure, was recorded globally by a network of induc-tion magnetometers at 18:33:27 UT. No significant phase delays of the signals were detected in four fre-quency bands at widely spaced observatories. It is sug-gested that the impulse can be excited in the Earth — ionosphere waveguide by a pulsed electric field which occurs in the ionosphere due to the short-term impact of ISW on the magnetosphere.

In the studies of the data received from DEMETER (orbit altitude above the Earth is about 700 km), we detected for the first time electromagnetic perturbations, which are due to the ionospheric modification by HAARP, a high-power high-frequency transmitter, simultaneously in the extremely low-frequency (ELF, below 1200 Hz) and very low-frequency (VLF, below 20 kHz) ranges. Of the thirteen analyzed flybys of the satellite above the heated area, the ELF/VLF signals were detected in three cases in the daytime (LT = 11–12 h), when the minimum distance between the geomagnetic projections of the satellite and the heated area center on the Earth’s surface did not exceed 31 km. During the nighttime flybys, the ELF/VLF perturbations were not detected. The size of the perturbed region was about 100 km. The amplitude, spectrum, and polarization of the ELF perturbations were analyzed, and their comparison with the characteristics of natural ELF noise above the HAARP transmitter was performed. In particular, it was shown that in the daytime the ELF perturbation amplitude above the heated area can exceed by a factor of 3 to 8 the amplitude of natural ELF noise. The absence of the nighttime records of artificial ELF/VLF perturbations above the heated area can be due to both the lower frequency of the heating signal, at which the heating occurs in the lower ionosphere, and the higher level of natural noise. The spectrum of the VLF signals related to the HAARP transmitter operation had two peaks at frequencies of 8 to 10 kHz and 15 to 18 kHz, which are close to the first and second harmonics of the lower-hybrid resonance in the heated area. The effect of the whistler wave propagation near the lower-hybrid resonance region on the perturbation spectrum recorded in the upper ionosphere for these signals has been demonstrated. In particular, some of the spectrum features can be explained by assuming that the VLF signals propagate in quasiresonance, rather than quasilongitudinal, regime. It is noted that the profile and dynamics of the ELF perturbation frequency spectrum conform to the assumption of their connection with quasistatic small-scale electron-density inhomogeneities occurring in the heated region and having lifetimes of a few seconds or more. The possible mechanisms of the ELF/VLF perturbation formation in the ionospheric plasma above the high-latitude HAARP facility at the DEMETER flyby altitudes are discussed.

A series of experiments on modification of the ionosphere by a powerful ground HF transmitter was performed using the EISCAT heating facility in order to generate artificial magnetic pulsations in the frequency range 0.1–3 Hz. In several cases, the ionospheric electric field and the electron density vertical profile were measured with the EISCAT incoherent scatter radar. The measurement of the background values of the ionospheric parameters made it possible to verify the numerical model for generating artificial emissions. The calculated amplitudes of magnetic pulsations correspond to the values measured on the Earth’s surface. However, the model cannot explain the sporadic nature of artificial signals, which indicates that this model is incomplete. Disturbances of the neutral particle density in the upper atmosphere are one of the possible causes explaining a difference between the calculations and the experimental values. The numerical simulation indicated that the amplitude variations caused by such disturbances can be 20%. For artificial emissions whose intensity is comparable with the intensity of artificial noise, variations in the neutral components can result in the disappearance of an artificial signal on the spectrogram.

Experiments on the generation of artificial electromagnetic pulsations constitute an important part of investigations of the magnetosphere-ionosphere system with the use of an active action. The investigation of the generation of magnetic pulsations in the Pc1 frequency range has shown that the response of the ionosphere to heating is detected only in a few experiments. Although the primary perturbed parameter is the electron temperature, the efficiency of the generation of pulsations is determined by the perturbations of the ionospheric conductivity. The magnitude of these hertz perturbations depends complexly on the electron density profile and the parameters of a pump wave. The numerical experiment demonstrates the determining effect of the electron density in the D region on the magnitude of perturbations of the ionospheric conductivity. Under conditions of a low electron density, it is impossible to create a large perturbation of the conductivity in the Pc1 frequency range, although perturbations of the electron temperature can be large in this case. In view of a large number of electrons at altitudes of 70–90 km, which absorb a considerable fraction of the energy of a high-frequency wave, the electron temperature in the E region of the ionosphere cannot be sharply increased, but the amplitude of the variations of the ionospheric conductivity in this case is larger than that for the profiles with a low electron density. In the presence of the developed D region, the efficiency of the modification of the conductivity in the indicated frequency range can be increased by choosing the optimal frequency and polarization of the pump wave. A low efficiency of the experiments on the generation of artificial magnetic pulsations in the Pc1 frequency range is apparently explained by the fact that they were performed in winter in the absence of a well-developed D region of the ionosphere.

During last decade series with the EISCAT Heating Facility were carried out with the purpose of producing artificial magnetic pulsations in the 0.1 - 3 Hz frequency range. For several experiments the EISCAT radar provided measurement of ionospheric electric field and electron density. Numerical model of artificial pulsation excitation has been verified. The predicted amplitude of the pulsation is in accordance with the measured values, however model could not explained sporadic nature of the artificial signals. Variations of neutral spice densities are a possible way to explain this feature. Numerical modelling shows strong dependence of the conductivity modification on neutral density. Experiment on generation of artificial magnetic pulsations in Pc1 frequency range on November 19, 1998 is discussed in the framework of numerical simulation. Clear ionospheric response is observed during the first hour of the heating at 120-km distance by induction magnetometer but the artificial signal at the modulation frequencies disappeared for the next hour of the heating. The main ionosphere parameters do not show significant variations during this experimental run. Disappearance of artificial pulsations may be related with density variations of the neutral components of ionosphere. 1. Experimental results and objectives

On November 19, 1998, time interval 15.30-17.30 UT, an experiment on generation of artificial magnetic pulsations in Pc1 frequency range was carried out. The pump wave was modulated with three frequencies of 1, 2 and 3 Hz; each modulation frequency being used for 5 minutes. The heating wave frequency was 5.423 MHz; for three modulation cycles the pump wave polarisation was Ordinary (o-mode) and then for one cycle it was changed to eXtraordinary (x-mode). Clear ionospheric response is detected during the first hour of the heating at 180-km distance by induction magnetometer. A very interesting feature of the ULF emissions at 1 Hz is seen in the time interval 16.20-16.25 UT: pulsation amplitude is significantly increased, especially in D-component. EISCAT radar electron density and electric field measurements do not exhibit any changes in the ionosphere for this interval. However, natural pulsations of decreasing frequency indicate the resonance frequency of the Ionospheric Alfven Resonator (IAR) before this modulation cycle. It seems to be around 1 Hz and the growth of artificial pulsation intensity observed on the ground may be interpreted in terms of IAR eigenmode excitation.