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A cold flow-field study of a rapid expansion, Mach 4.73, two-dimensional multiple nozzle array has been carried out in the hypersonic wind Tunnel. The nozzles are of the type used in a gas dynamic laser where the quality of the downstream flow field is important. The report examines the uniformity of the flow field in such a multiple nozzle array. Tests were conducted at supply conditions of 45 psia and 540 deg R. Pitot pressure, static pressure, and total temperature were measured along the axial, vertical, and horizontal centerlines within the nozzle and 21 nozzle exit heights downstream. Shadowgraph pictures provided qualitative flow field observations. The shock structure consisted of sidewall shocks, nozzle trailing edge shocks, and nozzle throat shocks. Viscous phenomena consisted of the boundary layers on the sidewalls and contoured walls, as well as the turbulent wakes caused by the trailing edges of the center nozzle blades. Mach number, static temperature, static density, and velocity profiles are presented. This flowfield information is useful to the prediction of the degradation of beam quality resulting from the non-homogeneity of a gas-dynamic-laser flowfield.
Numerical solutions for CO2-N2 gasdynamic laser gain and maximum available power are used to examine the influence of nozzle throat radius of curvature and throat height on laser performance. Conventional gasdynamic laser nozzles incorporate minimum length supersonic contours with sharp throats in order to obtain rapid vibrational freezing of the gas. The study considers the effect of complete rounding of the throat (on both the subsonic and supersonic sides), up to a radius of cruvature equal to three throat heights. Such rounding allows easier manufacture and alignment of the nozzles, and should result in improved flow quality. The present results show a 15-percent reduction in laser gain and maximum available power due to complete rounding of the throat. (Author).
It is well established that population inversions between the (001) and (100) vibrational energy levels of CO2 can be created by rapid expansions of CO2-N2-H2O or He mixtures through supersonic nozzles. New experimental results are presented for such inversions. These experiments were conducted in both the 3-Megawatt Arc Tunnel and the 12.7 cm Shock Tunnel at the Naval Ordnance Laboratory. The results support previously published theoretical predictions obtained with a numerical, time-dependent, nonequilibrium nozzle flow analysis employing a simplified vibrational kinetic model. This theory is also compared with experimental data obtained by other investigators. (Author).
Interferometric studies have been performed in the test section of the Naval Ordnance Laboratory (NOL) 127 mm shock tunnel under conditions that closely simulate the flow in a gas dynamic laser (GDL) cavity. A Mach-Zehnder interferometer has been used to determine the density distribution in two nozzle configurations. In a two-dimensional fast-expanding nozzle, time-resolved interferograms were obtained at 200 microsecond intervals. For a multiple nozzle module interferograms were obtained in two mutually perpendicular directions. The experimental setup is described and the results are discussed. (Author).