EXPERIMENTAL INVESTIGATION OF SUPERSONIC FREE-VORTEX FLOW WITH LARGE ASYMMETRY FOR AERODYNAMIC LASER WINDOWS

A free-vortex supersonic nozzle with large asymmetry and minimum lengt h was developed for aerodynamic laser windows. The validity of the noz zle contour was confirmed by a comparison between the density distribu tion obtained from a Mach-Zehnder interferogram at the nozzle exit and that from an isentropic calculation. The pressure characteristics of the laser window strongly depended on the diffuser geometry and its co nfiguration. By optimization of the flowfield, the pressure ratio of t he laser window was increased to 50. This value is almost 3 times larg er than that of a conventional laser window. It was found that the opt ical quality of the laser window was determined mostly by the shear fl ow instability on the atmospheric side of. the supersonic jet. Based o n pressure measurements, a scaling of pressure recovery of the diffuse r is discussed so as to exhaust the jet to the atmosphere.