Seedless velocimetry of high-enthalpy hypersonic boundary layers by nitric oxide ionization induced flow tagging and imaging at 100 kHz

This Letter describes the first, to the best of our knowledge, demonstration of a velocity measurement by nitric oxide ionization induced flow tagging and imaging (NiiFTI) of a high-enthalpy hypersonic flow utilizing naturally formed nitric oxide. The measurements were conducted in the hypervelocity expansion tunnel (HXT) at Texas A&M University in Mach 8.5 and Mach 10 flows near an ogive test article. The region of interest contained boundary layers (BL) and the hot flow region behind the oblique shock front. The BL profiles were recorded with the velocity ranging between 2516 m/s and 985 m/s measured as close as 0.5 mm to the model surface. Single-shot measurement in the core flow showed an average velocity of 2.5 km/s with a slight decelerating trend. Overall, NiiFTI demonstrated a good performance in high-enthalpy hypersonic flow, extending its usability to reacting environments.