Conventional wind tunnel flow measurement techniques typically involve the use of intrusive sensor systems, such as Pitot-probes and transducers which come in contact with the flow. Intrusive methods become impractical for high Mach number flows, as such methods can cause considerable disruption to the integrity of flow measurements. Therefore, it is desirable to utilize non-intrusive methods in such experiments, especially as hypersonic flow conditions are achieved. Schlieren and shadowgraph imaging methods have been used successfully for decades as a method of non-intrusive flow visualization. However, these methods become obsolete when the path of light is obstructed, which is a common problem when analyzing concave surfaces and complex geometries.

The goal of this project was to develop a scalable krypton planar laser induced fluorescence flow visualization system for use on curved-surface geometries in sup- port of the hypersonic Boundary Layer Transition (BOLT) program. The system was designed to fit multiple wind-tunnel facilities, including the AEDC Tunnel 9 hypersonic test facility and UMD Ludwieg Tube.

In order to design and test the system, the AEDC Mach 3 Calibration wind tunnel was utilized and Kr-PLIF measurements were taken about a 0.50” spherical model and 2” BOLT model. A wide variety of equipment and methods were assessed for their suitability of this project, including 3 cameras and 7 sheet combinations.

A beam from a single-diode Ti-Sapphire laser was amplified, modulated, and shaped in order to create a thin laser-sheet of 0.25-1.0” width and 0.01”-0.025” thickness, frequency of 1 kHz, and pulse width of 40 fs. The flow was seeded with 5% krypton, and tests were conducted at Mach 3.

The results were compared to Schlieren imaging tests conducted onsite in the same Mach 3 wind tunnel. The Kr-PLIF method was moderately successful in finding regions of relatively high flow density, such as boundary layers and leading edges at an angle-of-attack. Additionally, Kr-PLIF was able to make measurements about the curved region of the BOLT model, which was previously unobservable by Schlieren imaging.