A technique for determining relaxation times by free-flight tests of low-fineness-ratio cones; with experimental results for air at equilibrium temperatures up to 3440 K
National Aeronautics and Space Administration, 1960 - Science - 55 pages
This report describes a technique which combines theory and experiments for determining relaxation times in gases. The technique is based on the measurement of shapes of the bow shock waves of low-fineness-ratio cones fired from high-velocity guns. The theory presented in the report provides a means by which shadowgraph data showing the bow waves can be analyzed so as to furnish effective relaxation times. Relaxation times in air were obtained by this technique and the results have been compared with values estimated from shock tube measurements in pure oxygen and nitrogen. The tests were made at velocities ranging from 4600 to 12,000 feet per second corresponding to equilibrium temperatures from 35900 R (19900 K) to 6200 R (34400 K), under which conditions, at all but the highest temperatures, the effective relaxation times were determined primarily by the relaxation time for oxygen and nitrogen vibrations.
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angle for frozen angle of attack angular coordinate apex appendix APPROXIMATE THEORY assumed blunt bow shock wave bow wave angle bow wave shape constant corresponding curve density ratio displacement thickness effective relaxation equation A20 equilibrium flow equilibrium temperatures experimental results feet per second figure l6 Free-Flight free-stream Mach number frozen and equilibrium frozen flow function gases half angle Hypersonic laminar boundary layer measured models were fired molecular vibration NACA TN nonequilibrium flow oxygen and nitrogen oxygen and pure oxygen dissociation plotted Polar coordinates pressure coefficient pure oxygen radial coordinate ratio of specific reference conical flow relation relaxation time parameter Reynolds number semicone angle shadowgraph data shock tube shock wave angle shock-tube tests SHOCK-WAVE SHAPE shown in figure solid cone angle specific heats supersonic air stream temperature ratio theory Thermodynamic Equilibrium turbulent boundary layer value of uQ values of Tp variations velocity vibration and dissociation vibrational relaxation yaw angle