| To study the variations of state parameters and chemically reacting flows of gases with simple molecular structures under different shock conditions,the radiance for time dependence of shock-heated methane as well as argon is measured,thus their shock velocities and temperatures are determined. Then chemically reacting flow fields of them are simulated by means of hydrodynamic theory. In this paper,methane and argon are respectively investigated.Aluminum target chambers filled with gaseous samples are impacted by projectiles (tungsten alloy WggMogNFei) which are accelerated by a two-stage light gas gun. The velocities of projectiles impacting targets are measured by means of a magnet velocity induction system (MAVIS). The radiance signals of gases compressed by shock waves are recorded by an instantaneous six-channel optical pyrometer system,thereof the shock velocities and the temperatures in shocked gases can be gained. Methane (as a typical poly-atomic molecule gas) and argon (as a typical inert gas) are investigated through shock experiments respectively. In each experiment,the unshocked specimen is in the state of normal atmosphere and room temperature.In the experiments with gaseous methane,when the velocities of projectiles are 4.8km/s,4.9km/s and 5.1km/s,the measured shock velocities in methane are 8.4 +0.2 km/s,8.6+0.2km/s and 8.9+0.3km/s,respectively. The radiance signal of every channel rapidly rises to a maximum with time,then slightly falls,which indicates that the thermal radiation of shock-compressed methane is in a thermodynamic non-equilibrium state. Assuming that local thermodynamic equilibrium (LTE) is reached during shock loading,the seeming radiance temperatures of methane gases under shock conditions mentioned above are 4020 + 60K,4180 + 80K and 4390 + 90K,respectively,using the fit of inequable-weight least squares procedure to the data of six channels. By this work,it is found that although shock in gaseous methane is very strong,the temperature in shock downstream is very low,and shock-induced thermal radiation of gaseous methane is in a non-equilibrium process. These data is instructive to the simulation of shock flows for methane.In the experiments with gaseous argon,when the velocities of projectiles are 1.78km/s,2.00km/s and 2.76km/s,the measured shock velocities in argon are 3.86+0.08km/s,4.10+ 0.09km/s and 5.30+ 0.12km/s,respectively. When projectile velocity is 1.78km/s,which is corresponding to the radiation properties of 'optically thin medium',i.e. absorptivity of shocked argon is a very small constant (independent of wavelength). When projectile velocity is 2.00km/s,the radiant intensities of the gas in the shock downstream linearly or exponentially varied with time. These results indicate that the absorptivities of the shocked argon are dependent of different wavelengths and the optical depth of the shocked argon is situated between that of 'optically thin medium' and that of 'optically thick medium'. When projectile velocity is 2.76km/s,the radiant intensities of the gas in the shock downstream exponentially varied with time. The regular pattern of radiance for shocked argon is observedthrough the shock experiments,which gives direct evidence to study the luminous mechanism of gaseous argon under shock compression.Reshocked argon spectra with time resolution at 1.8km/s projectile velocity are measured by means of an optical multi-channel analyzer (OMA). But the signals of single-shocked argon spectra with time resolution are so weak that they cannot be observed. It is further demonstrated that the radiation intensity of single-shocked argon is far smaller than that of black body at the corresponding temperature. Besides,a relatively strong spectral band near 405nm wavelength for re-shocked argon is found,which may be caused by the jumps of bound-free states or of free-free states for atomic argon.For gaseous methane,the one-dimensional multicomponent reacting flow in thermochemical nonequilibrium behind a normal shock wave is computed from an inviscid an... |
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