| New, laser-based diagnostic techniques, developed primarily within the combustion community, offer considerable promise for future application in aerodynamic ground test facilities. Two such nonintrusive diagnostic techniques, laser-induced fluorescence and Rayleigh scattering, are under development at Wright Laboratory with the goal of advancing capabilities for determining gasdynamic properties in hypersonic flowfields.; Laser-induced fluorescence temperature measurements were attempted in a static test cell for temperatures below 300 K. Initial tests of the laser-induced fluorescence technique were difficult to perform because of excessive scatter and fluorescence off the walls of the test cell. Optical corrections to eliminate the excess scatter resulted in reduced and unreliable signal levels. Theoretical modifications to the system were examined in an effort to extend the capabilities of the laser-induced fluorescence technique toward measurement of temperatures in the range 50-100 K. Modifications to the system include an expected increase to the laser beam energies and a change in the oxygen rotational energy transition used. According to theoretical analyses performed, these modifications should result in significantly higher fluorescence signals thus enhancing the capabilities of the prototype system.; Development of the Rayleigh scatter measurement system began when the prototype laser-induced fluorescence measurement system was reconfigured and relocated to the Mach 6 High Reynolds Number Facility. However, several adverse effects, such as extraneous scatter off tunnel surfaces and condensation of flow constituents, hinder efforts to obtain accurate Rayleigh scattering measurements. In spite of these difficulties, measurements have been achieved while the Mach 6 test section was pumped to a vacuum, as well as for actual tunnel operation for various stagnation pressures at fixed stagnation temperatures. Stagnation pressures ranged from 0.69 MPa to 6.9 MPa at fixed stagnation temperatures of 511, 556, and 611 K. Rayleigh scatter results show signal levels much higher-than-expected for molecular scattering in the wind tunnel. Scatter measurements have been made in the flowfield of a 8-degree half-angle blunt nose cone with a nose radius of 1.5 cm. Preliminary efforts have been made to correct for the offset, caused by condensation scatter, in the Rayleigh scatter measurements. The corrected Rayleigh scatter measurements have been compared to Computational Fluid Dynamics data. |
