Applications of single-beam 100  kHz krypton tagging velocimetry in high-pressure N₂ flows

High-repetition-rate krypton tagging velocimetry (KTV) has recently gained increased attention in high-speed flow diagnostics due to the nontoxic and nonreacting characteristics of krypton. We report the recent progress in developing a single-beam 100 kHz KTV system to characterize transonic/supersonic gaseous flows, focusing on high-pressure nitrogen environments. This technique has potential applications in various aerospace-related operations of nitrogen flows, including large-scale transonic/supersonic wind tunnel facilities and next-generation propulsion systems for space exploration. The performance of the single-beam KTV system is assessed in terms of relevant aspects commonly encountered in large-scale, high-speed wind tunnel facilities, including long focal length, high pressure, low krypton seeding, and wall effects. The effectiveness of the single-beam 100 kHz KTV system was demonstrated by conducting quantitative flow velocity measurements in the shear layers of a supersonic-free jet with high velocity gradients and a transonic boundary flow near a solid wall. The uncertainty of the KTV measurements is estimated to be about 4.0% at the center of the supersonic jet flow based on the standard deviation (i.e., 2σ) of the measurement data, with the corresponding standard error of the mean (i.e., 2σ/N) being 0.7%.