High-Signal, Unseeded Molecular Tagging Velocimetry in Hypersonic Nitrogen Flows

ABSTRACT: Velocimetry measurements in large-scale hypersonic test facilities are challenging because intrusive physical probes produce shock waves that disturb the flow field and conventional seeded methods require injection of particles or gas that are unacceptable. Seedless velocimetry techniques, such as Molecular Tagging Velocimetry (MTV) have been very successful in supersonic flows, but are challenging in this particular application because the flow is pure nitrogen, limiting the molecular species available for tagging. We propose to develop a novel MTV technique for seedless velocimetry measurements in high-speed flows, coined N2 MTV. Previous implementations of the MTV technique in nitrogen flows have yielded relatively low signal levels. N2 MTV will have significantly more signal, enabling its use in large-scale hypersonic facilities with multiple, simultaneous measurements. In Phase I, we will demonstrate N2 MTV for the first time in small-scale laboratory flows, and analyze and design a full- scale system to be developed in Phase II. In Phase II, we will develop and demonstrate a full-scale N2 MTV system in a relevant large-scale hypersonic flow facility. Our team is uniquely qualified to perform the proposed research program and includes an experienced program manager, an engineer who trained in MTV methods, and a leading academic expert. BENEFIT: Technology developed under this program will be in the form of a novel, advanced laser diagnostic for velocimetry in high-speed nitrogen flows. This technology will directly benefit researchers working on hypersonics research in large-scale facilities. The technology is generally applicable beyond hypersonic flow testing to any velocimetry application where other MTV approaches are limited, such as low humidity airflows.