Fluctuating Flowfield Density Measurement Over Wide Mach Number Range

The Army has identified a need for fluctuating flowfield density measurements over a wide range of velocities. We propose to employ a new non-intrusive optical diagnostic technique which is applicable over a Mach number range from subsonic to hypersonic. The method is based on spectially filtered rotational Raman scattering and uses a newly developed ultraviolet solid state laser system, in conjuction with an atomic mercury vapor filter at 254.7 nm. The filter is used yo block elastic and Rayleigh scattering, and transmit rotational Raman scattering. The use of an ultraviolet laser, and atomic vapor filter (as opposed to conventional spectrometer), results in significantly greater sensitivity than that of traditional vibrational Raman scattering. Modeling calculations indicate a potential density accuracy of +/- 1% at mean densities as low as 0.002 amagat. In this effort we propose a detailed study, including laboratory proof-of-concept measurements. An isotopically pure Hg vapor filter will be constructed, and its absorption characteristics determined. The study will employ a new, state-of-the-art, injection-seeded, frequency tripled, pulsed titanium-sapphire laser system. Extension to flow velocity and temperature measurement will also be explored.