A technique for the Monte Carlo simulation of the radiation in the carbon dioxide and nitrogen dissociation products in a shock wave is described: the rates of chemical reactions, as well as the excitation of electronic, vibration, and rotation levels of atoms and molecules of CO, CN, O2, and C2. A comparison of the results of numerical simulation and the experimental data obtained on shock tubes of the Institute of Mechanics of Moscow State University is presented.

An analytical model for calculating the radiation intensity in shock-heated air is constructed, taking into account the absorption of radiation as it passes across the shock wave along the observation beam of the measuring systems of experimental installations. Using the model, an assessment is made of the effect of absorption on the broadening of spectral lines, as well as on the radiation intensity of high-temperature air in the vacuum-ultraviolet and visible spectral regions.

Flight safety during the motion of a descent spacecraft in the Earth’s atmosphere primarily depends on the reliability of the heat-protective layer on its surface. Such layers typically consist of ablative carbon-based composite materials. This study of the ablation phenomenon is carried out from the point of view of the mechanical spallation of carbon microparticles from the graphite surface at a strong shock wave reflection from it. During the experiments, the emission of ablation products from the graphite surface behind the reflected shock wave was recorded including time profiles of the radiation and the time-integrated emission spectrum in the visible/infrared spectral range. Analysis of the obtained experimental data and theoretical estimations allow one to conclude that the main mechanism of the graphite surface ablation under the action of a strong shock wave is the mechanical spallation of carbon microparticles from the surface of the sample.

A series of experiments are conducted with the use of a shock tube at the Institute of Mechanics, Moscow State University to determine radiation absorption spectra in shock-heated oxygen in the wavelength range of 213–260 nm at a gas pressure of 1 Torr and shock wave velocities ranging from 3.4 to 4.5 km/s. Based on a comparison of the experimental data with the results of calculations using a spectral-kinetic model, the effect of bound–bound and bound–unbound transitions in the Schumann–Runge system on the absorption properties of oxygen is analyzed.

The self-ignition of a propylene–oxygen–argon stoichiometric mixture with a volumetric argon content of 95 C_2^ (λ = 553 nm) are analyzed. The ignition delay times τign are measured in the temperature range T = 1200–2460 K and pressures p = 4.5–25 atm. The data obtained are compared with the results of other authors.

Results of spectroscopic measurements of the equilibrium electron concentration behind a strong shock wave in argon at a shock-wave velocity of 4.2 km/s and a pressure ahead of the wave front of 5 Torr and in O2, N2, and air in the velocity range from 8.3 to 11.3 km/s at an initial pressure of 0.25 Torr are presented. The measurement method was based on an analysis of broadening of the hydrogen-atom Hβ line of the Balmer series in the spectrum of the integral radiation density of the studied gas to which a small amount of H2 was added ( 1

A series of probe measurements of low-temperature plasma parameters ahead of the front of the incident shock wave was carried out using a double-diaphragm shock tube DDST-M of the Institute of Mechanics of Moscow State University. Such investigations are needed for determining the electron concentration in front of the shock wave. This characteristic is important for the safety of the spacecraft flight since it's directly affects to communication problems during the descent and is necessary for adequate description of kinetic processes behind the shock wave. Nitrogen, oxygen, air, and argon were used as working gases. The results obtained make it possible to describe the processes of the photoelectric effect and photoionization of gas particles due to the hard radiation of a shock-heated medium, to evaluate the effect of these processes on the change in the probe potential, and to measure the electron concentration. The probe measurements were synchronized with the registration of the light flux, which was carried out using an avalanche photodiode and a 9-frame video camera located at the end of the shock tube. Data from the camera and piezoelectric sensors record the dynamics of the opening of the diaphragm, as well as the process of formation of a shock wave in the gas under study.

A model for the numerical study of radiation behind the front of a strong shock wave in a CO2-N2 gas mixture is proposed. The model is based on the direct statistical simulation Monte Carlo method and takes into account the physicochemical properties of atoms and molecules, translational-rotational and translational-vibrational energy transfer, kinetics of chemical reactions, excitation of electronic levels of atoms and molecules, as well as the processes of radiative energy transfer. A series of calculations of the spectral characteristics of a shock-heated mixture has been carried out. The results obtained are compared with the available experimental data.

The results of modeling the radiation characteristics of the air behind the front of a strong shock wave, performed using the direct simulation Monte Carlo method, are presented. The model used takes into account various physical and chemical processes occurring in shock-heated air, including the translational-rotational and translational-vibrational energy exchange, kinetics of chemical reactions, and excitation of electronic levels of atoms and molecules, as well as the emission and absorption processes for a discrete spectrum. As a result of the calculations, time-integrated spectrograms of the volumetric radiation power of shock-heated air are obtained in absolute units in the range of shock wave velocities from 7.4 to 10.7 km/s at a gas pressure in front of the shock wave front of 0.25 Torr. The calculation data are compared with the experimental data obtained on a DDST-M double-diaphragm shock tube of the Institute of Mechanics of Moscow State University.

The current state of research on measuring the electron concentration in low-temperature plasma in the vicinity of a strong shock wave, which simulates the conditions of the descend spacecraft entry into the Earth’s atmosphere, is considered. Various physicochemical processes leading to the formation of low-temperature plasma both ahead of the shock wave front and in the shock-heated gas are analyzed. A critical review of various plasma diagnostic methods is made, and their advantages and disadvantages are noted. Numerous experimental data on measuring the electron concentration in various shock-heated gases in various conditions are analyzed.

A series of probe measurements to determine the electron concentration in the gas ahead of a strong shock wave (SW) front are carried out using a modified double-diaphragm shock tube (DDST-M) of the Institute of Mechanics, Moscow State University. At the same time, the light flux from the region of the shock-heated gas is recorded, which makes it possible to calculate the electron concentration behind the SW using the spectroscopic method. The experiments are carried out in air, oxygen, and nitrogen at SW velocities ranging from 8.3 to 11.3 km/s and an initial pressure of 0.25 Torr in the low-pressure chamber (LPC). The dependencies of the electron concentration on the SW velocity and the distance from the observation point to the SW are obtained. The spectroscopic measurements make it possible to determine the dependence of the electron concentration on the composition of the gaseous medium. The obtained data are compared with the experimental data of other authors.

An extended version of the previously developed computational procedure SPECTRUM is presented, which allows us to calculate the radiation characteristics of a shock-heated gas, taking into account the decrease in the radiation intensity in an absorbing medium. The procedure is based on a line-by-line calculation of the emission and absorption spectra of the atoms and molecules that make up the studied gas mixture. When calculating the emission spectra of atoms and molecules, the values of spectroscopic constants are taken from well-known databases. The results of calculating the time-integrated spectral characteristics of shock-heated air are compared with the available experimental data obtained in the ultraviolet, visible, and infrared regions of the spectrum.

The problem of descent spacecrafts safety is closely related to the correct assessment of heat fluxes to their surface. This work is devoted to an experimental study of radiative heat fluxes that play an important role during the entry of a spacecraft into the Earth's atmosphere at superorbital velocity. The radiation properties of high-temperature air were measured in the detonation driven shock tube DDST-M at the gas pressure 0.25 Torr ahead of the shock wave in the shock wave velocity range from 7.7 to 11.4 km/s. The applied registration method fixates the time-integrated distribution of the radiation intensity of the shock heated air passing by the measuring cross section. The measurements were carried out in the spectral range from 190 to 1100 nm. Simultaneously, the evolution of the radiation power at certain wavelengths that are selected using monochromators was recorded. Time spectrograms at certain wave lengths make it possible to determine the effective process time that can be used to recalculate the measured integral radiation intensity to the radiation power that traditionally measures by 3-D spectroscopy method. A new spectral model is presented that performs a line-by-line calculation of the emission and absorption spectra of atoms and molecules. The experimental results are compared with the calculated data obtained using the spectral model, as well as data from other measurements.

Предложена модель для численного исследования излучения за фронтом сильной ударной волны в газовой смеси CO 2 –N 2 . Модель основана на методе прямого статистического моделирования Монте-Карло и учитывает физико-химические свойства атомов и молекул, поступательно-вращательный и поступательно-колебательный обмен энергией, кинетику химических реакций, возбуждение электронных уровней атомов и молекул, а также процессы переноса радиационной энергии. Проведена серия расчетов спектральных характеристик ударно нагретой смеси. Полученные результаты сравниваются с имеющимися экспериментальными данными.

We describe a technique for modeling the excitation of electronic levels, bremsstrahlung, and photoionization in the Monte Carlo method of direct statistical simulation. The simulation results are compared with known experimental and numerical data.

The radiation characteristics of shock-heated argon are measured in the shock-wave velocity range of 4.5 to 7.8 km/s at gas pressures ahead of the shock wave front of 0.25, 1.0, and 5.0 Torr. Time-integrated sweeps of radiation and the time dependences of the radiation intensity of shock-heated argon at the wavelength of 420 nm are obtained in absolute units. The results of direct statistical simulation by the Monte Carlo method of radiation-chemical processes in the argon behind the front of a strong shock wave are presented. The model takes into account the processes of excitation and ionization of an atom by electron impact, emission and absorption for a discrete spectrum, bremsstrahlung, photoionization, and photorecombination, as well as the broadening of atomic lines. The experimental and calculated data are compared.

The problem of flight safety of high-speed aircrafts is primarily related to the reliability of engines, which, in turn, depends on the correct understanding of the processes of ignition and combustion of fuel in the combustion chambers of engines during their design. In this work, a new method for registration the ignition of shock heated gaseous fuels using a thermoelectric detector is proposed. The detector well measures the ignition delay time of fuels in the microsecond range, which is characteristic of detonation processes in the combustion chambers of promising aircraft engines operating on detonation combustion. The efficiency of the detector is demonstrated by the ignition of a propane-air mixture behind a reflected shock wave as an example. During the experiments, the thermoelectric detector showed such properties as the ability to register high heat flux values, low inertia, high signal-to-noise ratio, and high temporal resolution. The data obtained are compared with the measurement data of the ignition delay time by optical and piezoelectric methods obtained in this work, as well as in the studies of other authors.

The results of measuring the integral and temporal spectral characteristics of shock-heated air are presented. The experiments are carried out on a modified two-sections SST-M shock tube of the Institute of Mechanics, Moscow State University in shock wave velocities ranging from 7.8 to 10.7 km/s and initial pressures in the low-pressure chamber of 0.125 and 0.25 Torr. The radiation wavelength range 115–195 nm, corresponding to the vacuum ultraviolet (VUV) spectral region, in which the main contribution to the radiation is made by the atomic lines of nitrogen and oxygen, is studied. The obtained radiation spectrograms are analyzed. The measurement data are compared with the available experimental data of other authors.

С помощью двухдиафрагменной ударной трубы DDST-M Института механики МГУ проведена серия зондовых измерений параметров низкотемпературной плазмы перед фронтом падающей ударной волны. В качестве рабочих газов использовали азот, кислород, воздух и аргон. Полученные результаты позволяют описать процессы фотоэффекта и фотоионизации частиц исследуемого газа за счет жесткого излучения от ударно-нагретой среды и оценить влияние этих процессов на изменение потенциала зонда. Зондовые измерения синхронизированы с регистрацией светового потока, которая осуществлялась с использованием лавинного фотодиода и 9-кадровой видеокамеры К011, расположенных в торце ударной трубы. Данные с камеры и пьезоэлектрические датчики регистрируют динамику открытия диафрагмы, а также процесс формирования ударной волны в исследуемом газе.

The integral and temporal spectral characteristics of shock-heated air in the shock wave velocity range from 7.35 to 10.4 km/s at a pressure p0 = 0.25 Torr before the shock wave front were measured. The experiments were carried out on the DDST-M shock apparatus of the Moscow State University Institute of Mechanics. The radiation wavelength range  = 600-1100 nm, corresponding to the visible and near-infrared spectral regions, in which the main contribution to the radiation is provided by atomic nitrogen and oxygen lines, was investigated. The analysis of the obtained integral in time spectrograms of radiation is performed. The peculiarities of time oscillograms for the most typical atomic lines of the spectrum are highlighted. The measurement data are compared with experimental data of other authors.