Spatially-resolved, nonintrusive measurements in a nonreacting scramjet combustor using laser-induced iodine fluorescence.

摘要

The theoretical development, calibration, and application of a nonintrusive optical flowfield-diagnostic technique utilizing laser-induced iodine fluorescence (LIIF) is reported. Experimental results from a combination of static cell and gasdynamic studies are used to quantify the thermodynamic scaling of the important collisional phenomena which strongly affect narrow-bandwidth-induced fluorescence of iodine seeded in air. With proper thermodynamic scaling, linecenter fluorescence signal relationships are developed for making measurements of iodine mole fraction, total number density, pressure, and temperature using narrow-bandwidth excitation. Complications in fluorescence signal interpretations arising from high-density broadening of adjacent lines into the linecenter of interest and from departure from the high-density limit are addressed and corrections are developed in order to extend the range of the optical technique. The number density and temperature measurement techniques are combined with velocity measurement into a unified, nonintrusive optical technique for simultaneous measurement of the flow properties in steady, compressible flowfields. A calibration experiment is performed in the known flowfield of an underexpanded jet. Comparison of the measurements with the numerical solution of the flowfield demonstrates the range and accuracy of the optical diagnostic technique. The calibrated technique is then used to characterize the mixing of supersonic streams in a model scramjet combustor. The experimental measurements will be used to quantitatively validate computational fluid dynamic (CFD) codes currently being developed to model the mixing process.