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A numerical study of underexpanded axisymmetric supersonic free jet issuing from supersonic nozzles having semi divergence angle of 0 deg and 7.5 deg at the nozzle exit was made using TVD finite difference scheme. The effect of nozzle exit angle on Mach disc position and Mach disc diameter was investigated numerically, and numerical results have been compared with schlieren observation. Favorable agreement was obtained between numerical results and schlieren pictures.

During measurements of atomic hydrogen in a silane plasma using two-photon-excited laser-induced fluorescence, laser-induced dissociation of the gas was observed. This was investigated until conditions for the input laser fluence were determined where the effect was negligible. A measurement of the atomic hydrogen distribution was then performed within the limits of these conditions.

Fluctuations of flow parameters in a jet are generated in the shear layer of the jet boundary as the backpressure is increased. To investigate fluctuations, it is desirable to perform experiments with nonintrusive diagnostic methods. In the present experiments, the laser-induced fluorescence method was used to measure the fluctuations of a low-density axisymmetric argon jet with high spatial and temporal resolution. With this technique, the critical Reynolds number above which fluctuations were generated in the shear layer was obtained, and the fluctuation distribution of the fluorescence intensity in the jet was also clarified.

Electron density and electrical conductivity are among the most important parameters governing performance of an MHD power generator. The far-infrared laser has offered a powerful diagnostic tool for measuring these quantities. However, clarifying the effects of the neutral gases and the laser beam refraction will improve accuracy. In the present paper, the variable-wavelength far-infrared laser was used to address these effects. In electron density measurement with a Michelson interferometer, the definite fringe shift due to neutral gases in the flame was detected, and the effects of neutral gases, especially the rotational absorption of water vapor, were quantitatively clarified. A method involving integrating beam intensity profiles is also suggested to account for the beam refraction effect of the conductivity measurements. The electron density and conductivity measured with corrections for these effects agree very well with theoretical calculations.

A thermally assisted laser‐induced fluorescence (LIF) detection system is developed to measure two‐dimensional spatial profiles of number density of alkali atoms seeded in an open‐cycle MHD generator, especially in the boundary layer on channel electrodes. The spatial resolution of this system is evaluated to be 1.3 mm. To assess the system, the LIF intensity from Na atoms used as a seed tracer is measured in a laminar air‐acetylene flame. The detected spatial profiles of the intensity show good agreement with those of the number density of sodium atoms measured by the spectral line absorption method. The LIF intensity near the surface of a cooled metal piece placed in the acetylene flame is also measured with this system as a preliminary experiment for applying it to the boundary layer on MHD channel electrodes.

An MHD generator as a commercially viable electrical source could offer a very efficient utilization of fossil fuel resources because of its high overall generation efficiencies. Investigations in recent years have confirmed this expectation, but there are many problems which are not yet resolved in regard to the gas dynamic characteristics of the MHD generators. The purpose of the present paper is to report the results of experimental studies of the steady supersonic flow in a Faraday-type MHD generator. The plasma for an MHD generator was produced using a shock tunnel. The color schlieren method was employed to observe the supersonic flow in a channel. The experimental results show clearly oblique shock waves and Prandtl-Meyer fans from electrode edges, and it is shown that, with an increase in the Lorentz force, the flow Mach number in a channel decreases and the shock changes its shape from an X type to a λ one.

Density profiles of potassium (K) were measured experimentally in a boundary layer on a cooled metal flat plate, and the K density was found to be higher than the estimated value without chemical reactions. Results of the boundary layer simulation with reactions and transport of chemical species showed that this enrichment of the K density was caused when the chemical species densities largely deviated from their thermochemical equilibrium values. The simulation also showed that this phenomenon might appear in a viscous sublayer in a turbulent boundary layer of an actual MHD power generation channel.

The electron velocity distribution function is the key parameter for understanding chemical kinetics in plasmas of discharge-pumped excimer lasers. Local and unambiguous determination of the parameter is presently only possible by the Thomson scattering, and this letter describes the first observation of the Thomson scattering signals from ruby laser light from an excimer laser. The results revealed otherwise inaccessible structure of the electron temperature, such as an increase of the temperature when the buffer gas was changed from helium to neon.