Chemiluminescent radiation from the far wake of hypersonic spheres.

Abstract

Radiation from the far wake of hypersonic spheres launched from a light-gas gun was measured with filtered photomultiplier radiometers. Projectile velocities ranged between 14,700 and 22,000 fps, with test section pressures of 30 to 220 torr. In all cases, the spectral distribution of the far-wake radiation was found to be consistent with the chemiluminescent recombination reaction NO + O —> N(>2 + hv. Further, various features in the radiative wake profile (intensity per unit wake length vs distance behind the body) were found to be correlated with the appearance of wake turbulence in schlieren photographs. The experiments indicate that the NO2 chemiluminescence is coupled to both the wake fluid dynamics and wake chemistry, and it is suggested that the NO2 chemiluminescence measurement represents an excellent observable with which hypersonic wake theories may be compared. The possibility of scaling the chemiluminescent results to larger bodies is briefly considered, and it would appear that all the quantitative features of NO2 wake radiation cannot be scaled because of important nonbinary processes occurring in the far wake.