Three-line fluorescence thermometry of optically thick shock-tunnel flow

Two-line fluorescence thermometry measurements based on excitation of the A-X (0, 0) band of nitric oxide were performed in the free-stream flow of a large-scale shock tunnel, the Arnold Engineering Development Center Impulse Facility. Because the flow is optically thick, effects of laser absorption must be taken into account. This can be accomplished by extending the two-line thermometry concept to three lines. We illustrate the three-line technique by combining two-line planar laser-induced fluorescence measurements from separate facility runs. The resulting free-stream temperature T(0) = 468 K ? 65 K is insensitive to assumptions regarding the laser propagation distance through the flow, the vibrational temperature of the flow, and the precise nature of the absorption line shape.