Development of an Onboard Sensor for Flow Field Properties for Hypersonic Vehicles

ABSTRACT: A sensor system will be developed for characterizing instantaneous flow fields around a hypersonic vehicle while in flight. Filtered Rayleigh Scattering (FRS) will be used to obtain spatially and temporally resolved densities in a plane near the body of the vehicle. Scattering from windows and surfaces will be suppressed using a vapor cell"notch"filter. Strategies will be investigated for using the notch filter to measure temperature and pressure as well. A prototype sensor will be constructed for ground testing on a slender cone model in a Mach 4 wind tunnel, a supersonic boundary layer tunnel, and on ionized flow produced in a plasma discharge chamber. The measured density fluctuations and their distributions should enable the optical characterization of flow field, information that is needed towards the development of onboard optical sensors, and for transmitting high-quality communication signals. To gauge the effects of the flow field on the quality of an optical beam, a laser beam will be traversed through it and the wavefront distortions measured using a wavefront sensor. BENEFIT: With renewed interest in hypersonic flight, Expendable Launch Vehicles (ELV) and Reusable Launch Vehicles (RLV) represent the future of space applications. A compact version of the proposed flow diagnostic using FRS would find use aboard hypersonic test vehicles and space vehicles. With private enterprises besides US Air Force and NASA entering the space launch vehicle market, there is a growing need for modular optical instruments that can interrogate flight environment under harsh conditions and thus enable the passage of high-quality communication signals.