Rayleigh and Raman scattering measurements have been performed i n the 20-inch, Mach 6 wind tunnel at the NASA Langley Research C e n t e r. Rayleigh results show signal levels which are much higher than expected f o r molecular scattering in the tunnel, while densities deduced from s p o n t a n e o u s Raman scattering of molecular nitrogen are in good agreement with t h e expected nitrogen densities in the facility. The apparent discrepancy in t h e Rayleigh result is attributed to cluster formation as a result of expansion i n the tunnel. The dependence of the Rayleigh signal on the stagnation p r e s s u r e and temperature is also discussed.

Using a narrow-band, pulsed, ArF excimer laser and a single-intensified CCD camera, planar laser Rayleigh scattering measurements were performed to obtain quantitative density measurements both in a free stream and in a model flow field in the 15-inch, Mach 6 high temperature facility at NASA-Langley. This facility is capable of achieving stagnation temperatures up to 700 K over a range of stagnation pressures from 0.35 to 2.07 MPa. The high temperature capability of this facility eliminates the clustering effect observed in earlier Mach 6 studies, and allows quantitative density measurements in the free stream over a range of stagnation pressures from 0.35 to 1.75 MPa. Model flow field measurements were obtained on a 38.1-mm diameter cylinder. Measurement locations include the free stream, the region behind the bow shock in front of the model, and the region behind the model including the wake. The densities deduced from the Rayleigh scattering measurements in the model flow field are compared with CFD computations. Measurement uncertainties and the detection limit are discussed. Abstract-Using a narrow-band, pulsed, ArF excimer laser and a single-intensified CCD camera, planar laser Rayleigh scattering measurements were performed to obtain quantitative density measurements both in the free stream and in a model flow field. These measurements were conducted in the 15-inch, Mach 6 high temperature facility at NASA Langley Research Center. This facility is capable of achieving stagnation temperatures up to 700 K (800 °F) over a range of stagnation pressures from 0.35 to 2.07 MPa (50 to 300 psia). The high temperature capability of this facility eliminates the clustering effect observed in earlier Mach 6 studies, and allows quantitative density measurements in the free stream over a range of stagnation pressures from 0.35 to 1.75 MPa (50 to 250 psia). Model flow field measurements were obtained on 38.1 mm diameter cylinder. Measurement locations include the free stream, the region behind the bow shock in front of the model, and the region behind the model including the wake. The densities deduced from the Rayleigh scattering measurements in the model flow field are compared with CFD computations. Measurement uncertainties and the detection limit are discussed.

Planar Rayleigh scattering measurements with an argon-fluoride excimer laser are performed to investigate helium mixing into air at supersonic speeds. The capability of the Rayleigh scattering technique for flow visualization of a turbulent environment is demonstrated in a large-scale, Mach-6 facility. The detection limit obtained with the present setup indicates that planar, quantitative measurements of density can be made over a large cross-sectional area (5 cm x 10 cm) of the flow field in the absence of clusters.

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