Numerical solution of strong radiation gasdynamic interactions in a hydrogen-seedant mixture

The absorption of laser energy in a flowing gas is analyzed by means of a two-dimensional numerical model. Gas properties for equilibrium hydrogen seeded with a trace amount of cesium are used to provide lowtemperature absorption. Radiation loss from the gas is ignored. The incoming 10.6 jtm beam has a Gaussian intensity profile and converges to a focus inside the nozzle. The conditions calculated correspond to fairly high subsonic Mach numbers where relatively low temperature rises are encountered. Parametric studies of laser power variations, gas velocity changes, inlet temperature changes, and pressure level changes are presented. In addition, two different focal lengths are used. The results show that increasing the pressure, the laser power, or the inlet temperature causes the absorption region to move forward in the nozzle, while decreasing the gas velocity causes the peak temperature to increase. However, both the peak temperature and the location of the absorption region are dependent upon a complex balance between many competing factors. The results suggest that stable flowfields are produced even when substantial fractions of the heat is absorbed aft of the focal point. In studying the effects of pressure or gas velocity changes, it is noted that the laser power should be normalized by the mass flow. Finally, the hotter temperatures on the centerline cause preferential absorption, so that an initially Gaussian intensity profile can reach zero intensity on the centerline while substantial power remains in the outer portion of the beam.