Strong Shock Waves In Air Research Articles

Radiation coupled chemical nonequilibrium normal shock waves

The problem of a normal shock wave in air or other gas with complex chemistry and coupled radiation is considered. Molecular transport properties are neglected and the gas mixture is assumed in translational, rotational, vibrational and electronic equilibrium with the local temperature. Only continuum radiation is included. Solutions are presented for strong shock waves in air, where air is assumed to consist of eleven species, N 2, O 2, O, NO, NO +, N +, O +, N + 2, O + 2, and electrons. When the usual methods of integrating ordinary differential equations are applied to the “stiff” equations of chemical nonequilibrium flow, it is found that the maximum step size is very small. Several methods which promise great improvement have appeared in the literature recently. These methods are shown to be special cases of a whole family of approaches, other members of which are superior in many problems. A proof of convergence is given. Solutions are obtained for the comparatively simple optically thin case, and with absorption of radiation behind the shock front. In the latter, the spectrum is broken into regions where the absorption cross section of each species is assumed only a function of temperature. The approximate solution to the radiative transfer equation is obtained by using the first order half moment equations.

Radiation coupled chemical nonequilibrium normal shock waves

The problem of a normal shock wave in air or other gas with complex chemistry and coupled radiation is considered. Molecular transport properties are neglected and the gas mixture is assumed in translational, rotational, vibrational and electronic equilibrium with the local temperature. Only continuum radiation is included. Solutions are presented for strong shock waves in air, where air is assumed to consist of eleven species, N2, O2, O, NO, NO+, N+, O+, N+2, O+2, and electrons. When the usual methods of integrating ordinary differential equations are applied to the “stiff” equations of chemical nonequilibrium flow, it is found that the maximum step size is very small. Several methods which promise great improvement have appeared in the literature recently. These methods are shown to be special cases of a whole family of approaches, other members of which are superior in many problems. A proof of convergence is given. Solutions are obtained for the comparatively simple optically thin case, and with absorption of radiation behind the shock front. In the latter, the spectrum is broken into regions where the absorption cross section of each species is assumed only a function of temperature. The approximate solution to the radiative transfer equation is obtained by using the first order half moment equations.

Effect of radiation on flow properties behind strong shock waves in air

Effect of radiation on flow properties behind strong shock waves in air

Rate of ionization behind shock waves in air

Knowledge of the ionization rate behind strong shock waves in air is essential not only for problems involving the flight of hypersonic vehicles at high altitudes, but it is also important for many interesting problems in atmospheric and geophysical research (e.g. the meteoric ionization problem). The main difficulty experienced in earlier studies (1) was the extremely fast rate observed at normal air densities, which kept the electron density profile behind strong shock waves beyond the spatial resolution of most ionization detectors that can be used for quantitative measurements. In the present investigation, the above-mentioned difficulty has been removed through the use of a 24 in. diameter, low-density shock tube, which allows experiments to be performed at densities lower than the ordinary shock tube operating density (2) by a factor of 100. By using such a shock tube, together with a microwave reflection probe, the electron density profile behind normal shock waves in air at density corresponding to an altitude of 250,000 ft (initial shock tube pressure, p 1 = 20 μ Hg) and in the velocity range 10,000 < U < 25,000 ft sec has been successfully measured. The preliminary results, which agreed grossly with a theoretical prediction by Lin and Teare, (3) indicated that at satellite velocity ( U ≈ 25,000 ft sec ), the thermal ionization process will be completed at a distance of about 1 cm behind the shock front; while at a velocity of 15,000 ft sec the corresponding distance will be about 10 cm. At other altitudes (up to about 300,000 ft, where atomic oxygen begins to appear in the atmosphere) the corresponding ionization distance may be scaled inversely to the atmospheric density since all the collision processes which govern the initial rise of the electron density profile are binary.

Calculation of Reaction Profiles behind Steady State Shock Waves. II. The Dissociation of Air

A numerical integration procedure has been used to investigate the reaction profile behind strong shock waves in air. The Mach number range from 8 to 15 was covered; the initial temperature was 300°K; and the initial pressures were 1 and 10 mm Hg. The dissociation reactions for O2, N2, and NO were considered along with the ``shuffle'' reactions N+O2⇄NO+O and O+N2⇄NO+N. No ionization reactions were included. Above Ms=10, the calculations show a pronounced transient maximum in the NO concentration. In addition, the rates of change of concentrations at constant volume of all species except O2 change sign under certain conditions. Several additional calculations were made which included an approximate treatment of the effects of a finite rate of vibrational excitation of O2 and N2. These calculations suggest that even at Ms=15, the vibrational excitation reactions have only a limited effect on the reaction profile. A calculation of the reaction profile for air at high pressure diluted with a large excess of inert gas at 3000°K showed that the Zeldovich mechanism approximately describes the production of NO under these conditions even though it fails completely for undiluted air at high temperatures.