The results of the numerical simulation of a pulse-periodic nanosecond discharge are presented. An axisymmetric high-frequency (5 MHz) electric discharge in a pin-to-pin configuration is considered. Numerical models are used that take into account the chemical kinetics of high-temperature air and plasma chemistry, in which the reaction rates are determined by the magnitude of the reduced electric field. Preliminary results of plasma activation of atmospheric pressure air by a pulse-periodic nanosecond discharge are presented in order to intensify the production of chemically active particles (by the example of atomic oxygen).

We present a numerical model of the main stage of a lightning discharge. Within the framework of the developed model, evolution of parameters of the current channel upon the return stroke (the lightning main stage) is described by the system of equations governing conservation of mass, momentum, total energy, along with the transmission-line equations for determining the electric potential and the total current in each channel cross section. The main characteristics of lightning at the stage of the return stroke detectable experimentally, such as gas heating in the channel to temperatures in the range of 10–40 kK, the fundamental possibility of propagation of the potential-gradient wave at a speed varying from several hundredth to several tenths of the speed of light, and the possibility of the return-stroke wave propagating a relatively long distance without substantial attenuation, are demonstrated numerically. The conclusion that the developed physical and numerical model of the lightning discharge describes physical processes that occur under real conditions qualitatively correctly can be drawn based on the results on simulation of lightning discharges of various intensity.

The results of the numerical simulation of a periodic surface barrier discharge are presented. The purpose of the work is to study the mechanisms of the impact of the discharge on the medium (air at atmospheric pressure) inducing the air motion over the dielectric surface. The numerical simulation was carried out using a computer model that implements the integration of a system of two-dimensional Navier–Stokes equations for the medium on the Twhole, the transport equations of charged particles and the Poisson equation for the electric potential. The particle deposition on the surface of a dielectric, which leads to charging of the dielectric, is considered in addition to volumetric processes (particle ionization, recombination, drift of charged particles in a strong electric field, concentration diffusion). Both force and thermal mechanisms affect the flow field in a periodic barrier discharge of small amplitude. The main effect of the discharge is the generation of a vortex flow, such that a jet with an average velocity of 1–2 m/s is produced along the surface.

Numerical modeling of the dynamics of a discharge initiated by a high-power femtosecond laser pulse in air at atmospheric pressure in pre-breakdown fields was carried out. Calculations were conducted within the framework of a 1D-axisymmetric model that describes the evolution of the radial profiles of the main parameters of the discharge under study. The model includes a system of reaction that determine gas heating and a detailed description of the kinetic processes in a given discharge, as well as a system of gas-dynamic equations to describe the expansions of the heated channel. The results of calculations of the breakdown time of the discharge gap are conсistent with the measurement data over the entire studied range of electric field strengths, E = 9–17 kV/cm. It is shown that one of the key factors determining the evolution of the parameters of a given discharge is the rate of gas heating.

Представлены результаты численного моделирования разряда постоянного тока в высокоскоростном воздушном потоке с использованием газодинамического кода Plasmaero. Моделирование плазмы разряда было выполнено с использованием одножидкостного МГД-приближения и детальной схемы плазмохимических реакций. В расчетах была получена динамика разряда постоянного тока (в том числе, возникновение перепробоя), которая качественно соответствует экспериментальным данным. Была получена и проанализирована концентрация атомарного кислорода в разных частях разряда. В нульмерном расчете получена оценка влияния наработанного атомарного кислорода на горение этилен-воздушной смеси. Было показано, что наработка атомарного кислорода в разряде постоянного тока может значительно уменьшить время индукции, что важно для стимулирования горения в высокоскоростном потоке.

В последние годы ведутся активные исследования электрических разрядов, используемых для воспламенения топливно-воздушной смеси и стабилизации фронта горения [1]. Для продольно-поперечного разряда постоянного тока было установлено, что процесс повторного пробоя происходит при необычно низком напряжении разряда. Этот процесс является лимитирующим фактором длины разряда в сверхзвуковом потоке воздуха. Для описания процесса повторного пробоя было проведено комплексное исследование, включающее эксперимент и численное моделирование в программах FlowVision и PlasmAero [2].

A physical and numerical model of a longitudinal–transverse discharge in a supersonic air flow is presented. The considered model takes into account not only the traditional mechanisms of interaction between the discharge and the flow (convection, diffusion, heat release, thermochemical nonequilibrium), but also the processes of dissociation and ionization in strong reduced electric fields. It is shown that, within the framework of a two-dimensional model of a direct current discharge, the current loop is carried away by the flow until the ionization rate due to a strong reduced electric field in the immediate vicinity of the electrodes provide a sufficient ionization to form an alternative current channel. In this case, a new current loop begins to form, and the old one dies off. The considered process of current reconnection has a periodic character. The current loop lifetime is proportional to the current amplitude.

A relationship has been established between the ignition timing of the region, activated by a high frequency corona discharge, and the autoignition timing of unburned gas in the hybrid HCCI engine in a propane-air mixture. This relationship depends on the equivalence ratio phi: the leaner the mixture, the weaker the dependence. For a richer mixture (phi = 0.7), autoignition is a sequential propagation of autoignition waves in unburned gas, in a leaner mixture (phi = 0.5) spontaneous ignition right away of the entire volume occurs just in front. It has been shown that autoignition event can be controlled by varying the discharge initiation timing, the configuration of discharge region, and the specific energy input into the streamer channel. These parameters are varied in wide range values, but occurrence of autoignition falls into suitable range of ignition angles corresponding to the optimal operating conditions of HCCI engine. It has been revealed that the controlling the onset of autoignition in a very lean mixture is less effective than in a richer one.

Results of numerical simulation using Plasmaero CFD code are presented for direct current (DC) discharge in a high-speed airflow. Modelling of plasma was performed using single-fluid MHD approach and detailed plasma-chemistry. As a result of simulation, the dynamics of DC discharge was obtained which corresponds to dynamics of this object registered during previous experimental study including such effect as the discharge re-breakdown. Concentration of atomic oxygen in different parts of discharge and near them was obtained and analysed. The influence estimation of obtained atomic oxygen concentration on the fuel mixture induction time was performed using zero-dimensional calculation. It was shown that atomic oxygen generation by DC discharge dramatically reduce the ignition delay that could be important for combustion stimulation in a high-speed flow.

Исследования характеристик электрического разряда в условиях высокоскоростного потока получили широкое развитие с начала 1960-х гг. [1] во многом в связи с острой необходимостью поиска новых эффективных технологий в области горения, аэрокосмической промышленности и преобразования энергии. В последнее время протяженный разряд постоянного тока, или дуговой разряд, рассматривается в основном применительно к задачам управления сверхзвуковым потоком [2], а также в работах по плазменно-стимулированному горению [3].

The transformation of various carbonaceous substances into ordered carbon nanostructures is a fundamental process in nanotechnology. Since this structural transformation is a common property of various methods for producing CNTs, understanding the mechanism of this process in the bulk of a plasma jet will be extremely important, since no substrates are used here. We present an experimental and numerical study of the synthesis of CNTs with and without external catalysts for the pyrolysis of soot, acetylene, and ethanol in a DC argon plasma at a pressure of 350 Torr. By combining various physical methods, including simultaneous thermal analysis, diffraction analysis, electron microscopy, and energy dispersive analysis, we will show that the aggregation state of the precursor significantly affects the structural and morphological properties of CNTs. Theoretical calcula-tions under the assumption of local thermodynamic equilibrium made it possible to study the gas phase composition of a plasma flow in which the CNT precursor is nucleated. It was found that during the pyrolysis of soot (C), the condensation temperature of solid carbon is 3672 K, with the hydrogen in precursor (C2H2) it is lower and equals 3353 K, with the addition of oxygen (C2H5OH) its value becomes even < 3141 K. At the lowest condensation temperature, the most thermally stable CNTs are formed.

The aim of the paper is to improve parallel algorithms that obtain higher precision in floating point reduction-type operations while working within the basic floating point type. The compensated parallel variants of summation and dot product operations for floating point vectors are considered (level 1 BLAS operations). The methods are based on the work of Rump, Ogita and Oishi. Parallel implementations in block and pairwise reduction variants are under consideration. Analytical error bounds are obtained for real- and complex-valued vectors that are represented by floating point numbers according to the IEEE 754 (IEC 60559) standard for all variants of parallel algorithms. The algorithms are written in C++ Compute Unified Device Architecture (CUDA) for Graphics Processing Units (GPUs) and their accuracy is tested for different vector sizes and different condition numbers. The suggested compensated variant is compared to the multiple-precision library for GPUs in terms of efficiency. The designed algorithms are tested in Krylov-type matrix-based methods with preconditioners that originate from different challenging computational problems. It is shown that the compensated variant of algorithms allows one to accelerate convergence and obtain more accurate results even when the matrix operations are in base precision.

A computational model of high-current pulsed arc discharge in air is proposed. This is, in general, a 2D model which takes into account the gas dynamics of the discharge channel, real air thermodynamics in a wide range of pressures and temperatures, the electrodynamics of the discharge including the pinch effect, and radiation. The 1D version of the model is tested and verified on several numerical and experimental works reported recently. It is concluded that low and moderate current discharges are satisfactorily described with the model. The model was then applied to simulate the electric discharge in air for the currents 1–250 kA and characteristic rise times in 13–25 µ s, and the results of the calculations were compared with experimental ones. It was concluded that most characteristics of the discharge are predicted well. Namely, the arc column radius and shock wave position agree well with experimental data for all the current amplitudes and rise times considered. Radial distributions of temperature and electron density also satisfactorily agree with experimental data. It was found that the pinch effect should be considered for currents higher than 100 kA.

A new approach for creating composite nanoparticles with various morphology and electric properties, based on uniform‐sized small boron nitride (h‐BN) nanosheets and graphene flakes, is suggested. For the first time, the structures from h‐BN and graphene flakes synthesized in the helium direct current plasma jet are used to fabricate composite nanoparticles and films using 2D printing technology. A method for preparing a suspension based on these composite particles is developed. The morphology of graphene decoration with small h‐BN flakes depends on the composite content. It includes, for instance, graphene flakes covered with vertically arranged h‐BN flakes, graphene flakes encapsulated with a monolayer of h‐BN flakes. The electric properties of films and printed structures from composite nanoparticles are strongly varied (especially for the printed compositions). However, the graphene content in all cases is higher than the percolation threshold. Some composites demonstrate nonlinear current–voltage characteristics with the switching up to four orders of magnitude. In combination with the cheap printed technologies, the composite material is expected to be a perspective for electronic applications (informative processing, logic elements, tunneling graphene electronics, memristors, etc.).

This work focuses on detailed descriptions of DC discharge properties in supersonic airflow and its applicability in combustion simulations. Due to the complexity of obtaining most of the data in the experiment, our experimental research was supplemented by a numerical simulation. Two packages, i.e., FlowVision (fast commercial CFD for 3D engineering) and Plasmaero (2D scientific code developed in JIHT RAS for MHD tasks), were used for modeling the arc DC discharge in a supersonic flow at Mach (M) = 2. Both will be considered for further use in plasma-assisted combustion modeling, so it is important to validate both codes using experimental data from the model configuration with discharge. Axisymmetric geometries of experiments with two coaxial electrodes located parallel to the flow were chosen to avoid the appearance of the current channel part perpendicular to the flow and the corresponding discharge pulsations. Such geometries allow performing numerical simulations in 2D formulation, making it possible to compare the results obtained in the experiments and calculations. As a result of this work, two-dimensional distributions involving temperature, current density, chemical composition, and other discharge and flow parameters were obtained for arc DC discharges 0.5–7 A in a supersonic flow (Pst = 22 kPa, T = 170 K, V~500 m/s). Good qualitative agreement between experimental and numerical results was achieved. The production of a significant amount of atomic oxygen, which accelerates combustion, was noted.

The electric power generation in on-board MHD generator is considered under conditions of vehicle’s flight in Earth atmosphere. The physical and computational model of on-board MHD power generation is presented. It is shown that electric power of order of 18 – 20 MW (or ∼ 100 W/cm3) can be extracted in ordinary Faraday-type segmented MHD generator. This high level of electric power is achieved at magnetic field about 0.3 – 0.4 tesla and constitutes nearly 9.5% of total enthalpy flux. The main factor limiting the rise of extracted power is a stall of flow due to MHD deceleration.

In this paper we present numerical research of pressure waves influence on the end-gas in HCCI engine with discharge activation. It is shown that there is certain promotion of exothermic chemical reactions by pressure waves. That leads to the slight heating of the end-gas, but mainly the end-gas is heated due to the compression in the process of combustion wave propagation.