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.

High power, pulsed microwaves are beamed forward of a model in a Mach 6 flow using an on-board, Ku-band horn. A thin “precursor” plasma is generated just ahead of the bow shock in the low density free stream. Temporal and spatial analysis of the microwave E-field and plasma conductivity in the supersonic flow field indicate that the plasma reflects a large proportion of the microwave power in an individual pulse as soon as the plasma frequency exceeds the wave frequency. Possible methods for more efficient deposition of power in the free stream are discussed which could lead to increased interaction with the shock.

Using a cw tunable laser, absorption measurements were made to determine for the first time the shift and broadening of the ultraviolet transitions of OH induced by collisions with molecular nitrogen and oxygen. Similar measurements were also made for collisions with air and inert gases He, Ne, Ar, and Kr. Both the shift and broadening due to these collisions were found to depend linearly upon pressures in the range from 50 Torr up to 1 atm. The homogeneous linewidth for the P 1(2) transition ofOH in ambient air is determined to be (0.20±0.OO5) em-I. Results with Ar and Kr show contributions not accounted for by the polarizability of the colliding species.

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.

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