Femtosecond laser tagging velocimetry in hypersonic arc-jet airflow

Hypersonic flight and atmospheric re-entry simulations conducted in high-enthalpy ground test facilities aim to recreate the natural conditions of high altitude and thermally demanding flights. The current instrumentation used for measuring flow dynamics parameters and validating computational models lacks the capability for direct, nonintrusive measurements, largely due to its limited applicability in such hostile environments. Here we demonstrate direct and nonintrusive velocimetry measurements in the undisturbed hypersonic air flow and in the air flow near an object’s surface within an arc-heated test facility using Femtosecond Laser Electronic Excitation Tagging (FLEET). Tagging the intrinsic nitrogen molecules in air flow using a femtosecond laser and tracking them over time allowed for direct flow velocity measurements, offering high resolution while preserving the integrity of the flow. Our results pave the way towards the next generation of measurement and testing instrumentation for hypersonic aerothermal test facilities. While the characterization of the flow fields of arc-heated test facilities is complicated by the hostile testing environment, this work demonstrates that reliable flow characterization can be achieved using Femtosecond Laser Electronic Excitation Tagging (FLEET) optical velocimetry diagnostics. Aaron Gieder and colleagues report nonintrusive velocimetry measurements in both undisturbed hypersonic air flow and near an object’s surface within an arc-heated test facility.