Planar Laser Induced Iodine Fluorescence Investigation of Mach 5 Jet-Jet and Jet-Jet-Surface Interactions

During approach maneuvers with the International Space Station (ISS), an autonomous spacecraft performed an emergency procedure in order to decrease the closing rate as the spacecraft approached the space station. NASA Johnson Space Center had performed Direct Simulation Monte Carlo (DSMC) fluid dynamics simulations in order to certify the maneuver in the vicinity of the ISS. When the spacecraft performed the maneuver however, it resulted in exterior damage to the International Space Station.

Following the flight incident, the University of Virginia's Aerospace Research Laboratory engaged in high speed fluids research in an effort to ascertain the root cause of the differences in the computational model and real-world fluid dynamics observed during the HTV maneuvers. Planar Laser Induced Iodine Fluorescence was utilized as the spectroscopic method with which to qualitatively and quantitatively investigate the complex hypersonic flowfield. Qualitative broadband visualizations were collected to visually classify each flowfield, as well as determine quantitative flowfield geometry measurements. Visualizations were collected for numerous configurations including varying the number of exhausting jets (between two and four exhausting jets), varying the separation between neighboring jets, and for a variety of impingement standoff distances. Along with providing qualitative images of the flowfield interactions, quantitative flowfield density ratios were measured. The quantitative density ratio experiments were conducted for a smaller subset of experimental configurations. The combination of the qualitative images, geometry data, and density ratio data provides significant experimental insight into the complex jet-jet and jet-jet-surface interactions.

Results from the research presented herein led to three major conclusions. First, by increasing the jet spacing the neighboring jet interaction decreased, as expected. Second, the removal of two exhausting jets led to a 5 times smaller mixing percentage, which means mixing was enhanced by the two additional jets. Finally, for both the four jet and two jet flow configurations, the introduction of the impingement surface to the flow yielded an approximately 70% increase in total mixing percentage, which means there was an approximately 70% increase to the neighboring jet interactions. The data collected will be applied directly to the refinement of the NASA DSMC algorithm. The additional refinement of the analysis algorithm will result in changes to spaceflight operating procedures surrounding the approach and docking / capture process with the International Space Station.