Gasdynamic Regime Research Articles

Two gasdynamic propagation regimes of a subsonic optical discharge

A method was developed for recording the motion of gas in the region of an optical discharge which is based on observing the transport of specially created optical inhomogeneities by the gas. It was used to confirm the existence of a cold gas ahead of the discharge front and to obtain quantitative data concerning its motion. The conditions were realized for the propagation of an optical discharge plasma completely immersed in a laser beam, the laser radiation being only weakly absorbed in the discharge. A sudden change in the discharge front velocity on reaching the lateral surface of the laser beam indicated that the gasdynamic regime of the propagation of the slow combustion optical discharge had changed.

Investigation of thermal self-action (blooming) of intense beams in homogeneous gas flows

A brief survey is made of the papers devoted to the thermal blooming effect of laser beams in a gas in the presence of relative beam and medium motion. A classification is presented of the gasdynamic regimes of the thermal blooming effect and their qualitative distinction is displayed by using linearized equations. Fundamental attention is paid to regimes in which the gas velocity component transverse to the beam is a of the order of magnitude or greater than the sound speed.

Flow of electrically charged aerosols past bodies

An experimental investigation was made of the flow of electrically charged aerosols with solid or liquid disperse phase past bodies. Air flows with solid particles (sand, iron) and water drops were produced by special apparatus. The regimes in which the disperse particles and the bodies were charged or neutral were studied. A system of dimensionless numbers and their values are indicated for the different gas-dynamic and electric flow regimes. The main features of the flows are explained and the integrated electric characteristics of the bodies determined. The possibility of controlling the flow of a disperse medium by means of electric fields is demonstrated. It is shown that the inductive charging of liquid films near sharp edges of a body has a strong influence on the electric characteristics of the body (when air with water drops flows past it).

Modeling of the gasdynamic regime of an exploding water droplet in a high-power pulsed light field

A gasdynamic approach was used to investigate the problem of the explosion of a small water droplet of a CO2-laser field. The characteristics of the explosion were described as a function of the laser pulse parameters and the size of the droplets. Threshold conditions were determined for the realization of an explosion in the single-phase region. The later stages of the shock waves in air when droplets explode in laser beams were shown to be equivalent. It was shown that the optical transmission through an aqueous aerosol can be exhanced when the explosion of the droplets takes place in the gasdynamic regime.

Laser spectrochemical analysis of aerosols

The process of the diffusive evaporation of solid aerosol particles is studied theoretically and the gasdynamic evaportion regime is described qualitatively. From the expressions obtained for the temperature and density fields of the vapor in the neighborhood of a particle, expressions are derived for the electronic line-emission intensities from substances.

Precursor photo-ionization model for magnetically-driven transverse shock waves

Shock waves produced by magnetic compression are called transverse when the magnetic field contains no component in the direction of the shock wave normal. It is experimentally well known that very strong shocks of this type show classical MHD behaviour in terms of both jump conditions and structure. It is also known that relatively slow transverse shocks can be of an ionizing gasdynamic type with no jump in the imbedded transverse field. Since there are fundamental differences in both the structure and the jump relationships of these two types of shock waves, it is of interest to investigate the transition behaviour in the intermediate shock speed regime. A previously widely accepted model due to Kulikovskii & Lyubimov and Chu assumes no precursor ionization and requires significantly large values of the magnetic Prandtl number, Pm, within the shock structure. That model is shown to be physically inappropriate because experimentally observed transition speeds and corresponding post-shock temperatures imply negligibly small shock Pm values. Also in that model, MHD conditions are approached only asymptotically at large shock speeds. The present precursor ionization model assumes effectively zero Pm values throughout transition and into the low-speed MHD regime. As distinct from the previous theory, this model predicts the attainment of full MHD conditions at and above a well-defined finite shock speed. The assumption of a characteristic post-shock temperature model for the ionization mechanism allows unique jump relations to be formulated independently of other transport mechanisms. Results include computed values of various jump ratios and the electric field as functions of shock speed throughout gasdynamic, transition, and MHD regimes. The solutions form a one-parameter family depending on the relative combination of upstream magnetic field and density (e.g. the Alfvén velocity). Shock structure phase plane trajectories are computed at a number of typical shock speeds throughout transition.

Effect of External Radiation on the Burning Rates of Solid Propellants

A means for improving the performance of a solid fuel pulsed plasma thruster has been described and analyzed. The key to improvement is control over the mass consumed per discharge. Figures 3 and 4 show that the mass consumption can be chosen by adjusting the distance between the two side-fed Teflon fuel bars. For high mass consumption, the thruster operates in the gas-dynamic regime and provides high thrust. At low mass consumption, thruster operation is primarily electromagnetic with high specific impulse. Efficiency increases as the thrust mechanism is predominately in one regime or the other. By using side feed, the performance has been significantly increased over the conventional rear-feed design. Carbonization of the Teflon side walls remains the one stumbling block to the full utilization of this design to flight thrusters. Geometry changes may reduce or eliminate this problem. References