Simultaneous Multi-property Planar Laser Diagnostic for Hypersonic Flows

ABSTRACT: An unseeded measurement technique is proposed for simultaneous spatially-resolved measurements of density, temperature, and velocity in hypersonic wind tunnel flows with the future potential for time-resolved measurement capability. A variant of filtered Rayleigh scattering (FRS) will be developed that takes advantage of unique monotonic relationships between molecular vapor cell filter transmissions and flow parameters of interest. The method relies on laser Rayleigh scattering from naturally present nitrogen or air molecules, and therefore requires no seeding of the flow. Thermodynamic properties of the test gas are obtained by measuring the transmission of Rayleigh scattered light through multiple vapor cell filters, which have sharp spectral cut-offs that can be tailored to provide good sensitivity to the properties of interest. A unique set of transmission coefficients, measured from images obtained with a camera, defines a given thermodynamic state, providing a non-intrusive instantaneous measurement. In the Phase I effort, we will demonstrate the technique with instantaneous measurements of density, temperature, and velocity along a line in a supersonic flow, laying the groundwork for later variants that will enable two-dimensional measurements of these quantities in various hypersonic flow fields, e.g., boundary layers, shock-wave/boundary layer interactions, and time-resolved measurements at high acquisition rates.; BENEFIT: The unique capability of filtered Rayleigh scattering (FRS) to measure flow fields, ranging from subsonic to hypersonic, with high spatial resolution is expected to be attractive to a wide range of customers, including U. S. and other governments test facilities, universities, and industrial testing sites. The FRS scheme described in this proposal can simultaneously measure multiple flow properties without the need for flow seeding, and hence represents an excellent diagnostic tool that can benefit vehicle designers and flow modelers. Some attributes of FRS having value to commercial aerospace interests include measurements supporting performance testing of advanced aircraft, rotorcraft, entry spacecraft such as Expendable Launch Vehicles (ELV) and Reusable Launch Vehicles (RLV), and propulsion concepts. Equal measurement capability is not readily available elsewhere in the world, thereby offering U.S. Government laboratories and the U.S. aerospace industry a unique capability for aerodynamic vehicle development. FRS is adaptable to applications in facilities of all sizes including those for full-scale model testing of aircraft and inlet flows, rotorcraft intra-blade and rotor-body wake interactions, vortex-control surface interactions, in-flight flows, propulsion system testing, and rocket test stand plumes. Another attractive feature of the FRS technique is the ability to measure temperature and density in turbulent flames and swirl combustors non-intrusively.