Understanding the hypersonic flow physics around a high-speed vehicle informs its design: vehicle performance (lift and drag), thermal protection, controls, and structural design. A long run of over 50 years of research in this area is evidence of the difficult but potentially rewarding nature of this work. To date, computational tools used for design (i.e., computational fluid dynamics or “CFD”) can have difficulty predicting flow physics over simple geometries, much less entire vehicles. This is, in part, because there is a dearth of experimental data the computational community can use for validation; adequate measurement methods simply do not exist.

Here, researchers extend a method that enables measurements of velocity profiles in Mach 6 flows. This non-intrusive method is called Krypton Tagging Velocimetry. They use a clever combination of a burst-mode laser and an optical parametric oscillator to create high-intensity, deep-UV laser pulses (212 nm, 6 mJ/pulse, 100 kHz, ~100 pulses) which can excite, via resonantly-enhanced multiphoton ionization (2+1 REMPI), trace amounts of krypton that is seeded into the flow. That is, this setup can illuminate lines in the hypersonic, Mach 6 gas flow to create velocity profiles, much like tracing dye in a water flow to study flow structures.

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