Numerical Simulation of Air Flow in the State of Thermal and Chemical Nonequilibrium behind a Shock Wave Front

We used the model of a five-component air mixture flow behind the front of a one-dimensional shock wave to compute the flow parameters for shock front temperatures of up to 7000 K, taking into account the variable composition, translational and vibrational temperatures and pressure in the relaxation zone. Vibrational level population in oxygen and nitrogen obeys the Boltzmann distribution with one common vibrational temperature. We consider the effect that temperature nonequilibrium has on the chemical reaction rate by introducing a nonequilibrium factor to the reaction rate constant, said factor depending on the vibrational and translational temperatures. We compared our calculation results for dissociation behind the shock front to the published data concerning temperature nonequilibrium in a pure oxygen flow behind a shock wave front for two different intensities of the latter. The comparison shows a good agreement between the vibrational temperature, experimental data and calculations based on the experimental values of vibrational temperature and molality. We computed the parameters of thermodynamically nonequilibrium dissociation in the air behind the shock wave front, comparing them to those of equilibrium dissociation and calculation results previously published by others. The study demonstrates that the molality values computed converge gradually with those found in published data as the distance from the shock front increases. We list the reasons for the discrepancy between our calculation results and previously published data

Effects of geometric similarity ratio on the disturbance amplitude of shock-wave front in viscosity measurement

Geometric similarity ratio is one of the important factors that affects the disturbance amplitude of shock-wave front in viscosity measurement. In this paper, the Euler difference scheme of two-dimensional (2D) equations of viscous fluid mechanics is used to simulate the disturbance amplitude damping curves under different geometric similarity ratios, and the corresponding numerical solutions are shown. The samples of aluminum shocked to 80 GPa are taken as an example. The simulation results show that the initial conditions, material viscosity, wavelength, and sample geometric similarity ratio affect the evolution of the shock front sine wave disturbance. For flyer-impact flow field, the phase shift increases from 0 to a certain value with the viscosity coefficient for sample with wavelength [Formula: see text] mm and geometric similarity ratio [Formula: see text], 0.1. So, the geometric similarity method can be used to measure the viscosity of material. But it is found that the phase shift is sensitive to the geometric similarity ratio, which should be considered in Zaidel’s equation. So, some flyer-impact experiments will be carried out to determine the simulation results, and find the quantity relation of phase shift and viscosity of material in the future investigation.

Methods of simulating the front of the air shock wave for calculating the industrial structure

Introduction. The paper considers existing methods of simulating a wide front of an air shock wave for solving problems of shock wave interaction with an installation using gas-dynamic methods. When solving the problem of the air shock wave interaction with an installation in a dynamic setting, it was revealed that, when simulating a wide front of a distant explosion using point explosions, it is possible to obtain an underestimated time of the shock wave action. This results in a downward bias of loads to the installation. Thus, the loads obtained in this case do not correspond to the loads for which it is necessary to carry out the calculation of industrial installations protected from shock waves in accordance with domestic and international regulatory documents. To eliminate this drawback, another approach is proposed. It consists in setting the load on the computational region in the form of a pressure graph with specified parameters of overpressure and exposure time. Materials and methods. The interaction of the shock wave front with the installation is carried out using numerical simulation in a nonlinear dynamic setting using gas-dynamic methods in the LS-DYNA software package. Results. The following analyses were conducted in the scope of the study: an analysis of existing methods of forming the wide shock wave front of the distant explosion and an analysis of the parameters of the shock wave during the formation of the wide shock wave front of the distant explosion by setting the pressure graph with the specified parameters of the overpressure and the exposure time. Conclusions. The result of the analysis of methods for numerical simulation of the interaction of the air shock wave wide front with the installation showed that simulation of the explosion source in the form of volume elements and simulation of the shock wave using the CONWEP function of the LS-DYNA software package have disadvantages. These disadvantages do not allow obtaining the main parameters of the shock wave for the further use. A method for modeling the wide shock wave front is given by setting a pressure graph at the boundary of the computational region with the required overpressure parameters and exposure time.

Explosion of the boundary layer upon entry of spacecraft into dense layers of the Earth's atmosphere

Introduction/purpose: A supersonic flow around a sphere with a radius of 1m at altitudes of 80 to 40 km was analysed. Methods: The descent trajectory at the first cosmic velocity, similar to that of the Soyuz spacecraft with a duralumin structure without thermal protection, was taken into consideration. Results: For the gas between the shock wave front and the surface of the descending spacecraft, data were obtained on the increase in density, pressure, and temperature behind the shock wave front as well as the shift of the shock wave from the surface of the descending spacecraft. The effective temperature of the shock-heated gas reaches its maximum value of 7340 K at an altitude of 60 km. At altitudes of 80 and 40 km, the effective temperature is 7000 K and 6400 K, respectively. Based on the obtained data on the thermodynamic state of the gas behind the shock wave every 10 km, calculations were made of energy fluxes to the surface of the spacecraft for convective and radiative heat transfer, as well as for the impact of electrons produced due to ionization of negative ions. Radiative heat transfer has proven to be the most significant. The burning mechanism of negative ions of triatomic molecules of aluminium with the formation of AlO molecules was determined, and data on pressure rise in the boundary layer on the spacecraft surface were obtained. At all considered altitudes, the pressure rises instantly: to 1.06*1010 Pa at an altitude of 80 km, 5.3*10 Pa at an altitude of 60 km, and reaches the maximum value of 5.5*1010 Pa and an altitude of 40 km. A pressure of 109 to 1010 Pa arises during explosion of various explosives. The energy flux reaches the spacecraft surface between explosions. At the moment of explosion, shock waves develop in the atmosphere surrounding the surface of the descending spacecraft, and compressive waves develop in the entire structure of the spacecraft. The descending spacecraft cracks, and its entire structure breaks down into parts. The area of interaction increases sharply, and each subsequent explosion has a greater intensity and size. As a result, the last most intense explosion occurs at an altitude of approx. 40 km, after which individual fragments of the spacecraft fall to Earth. Conclusion: The exploration of space with flight to other planets is possible only after a thorough study of explosive processes taking place on the surface of the spacecraft descending on other planets, and especially on Earth.