The use of planar laser-induced fluorescence (PLIF) of nitric oxide (NO) was inves-tigated for use in visualizing wake flowfields downstream of rapid prototyping models in a hypersonic wind tunnel. The re-entry models for use in this study were fabricated using a stereo-lithography apparatus. These models were produced in one day or less, which is a significant time savings compared with the manufacture of ceramic or metal models. The models were tested in the NASA Langley Research Center 31-Inch Mach 10 Air Tunnel. Pure NO was either seeded through tubes plumbed into the model or via a tube attached to the strut holding the model, which provided localized addition of NO into the model's wake through a porous metal cylinder attached to the end of the tube. Various entry capsule model types and configurations and NO-seeding methods were used, including a new streamwise visualization method based on PLIF. Virtual diagnostics interface technology, developed at NASA Langley Research Center, was used to visualize the datasets in post-processing. The use of calibration ‘dotcards’ was investigated to correct for camera perspective and lens distortions in the PLIF images.

Reentry models for use in hypersonic wind tunnel tests were fabricated using a stereolithography apparatus. These models were produced in one day or less, which is a significant time savings compared to the manufacture of ceramic or metal models. The models were tested in the NASA Langley Research Center 31-Inch Mach 10 Air Tunnel. Most of the models did not survive repeated tests in the tunnel, and several failure modes of the models were identified. Planar laser-induced fluorescence (PLIF) of nitric oxide (NO) was used to visualize the flowfields in the wakes of these models. Pure NO was either seeded through tubes plumbed into the model or via a tube attached to the strut holding the model, which provided localized addition of NO into the model's wake through a porous metal cylinder attached to the end of the tube. Models included several 2-inch diameter Inflatable Reentry Vehicle Experiment (IRVE) models and 5-inch diameter Crew Exploration Vehicle (CEV) models. Various configurations were studied including different sting placements relative to the models, different model orientations and attachment angles, and different NO seeding methods. The angle of attack of the models was also varied and the location of the laser sheet was scanned to provide three-dimensional flowfield information. Virtual Diagnostics Interface technology, developed at NASA Langley, was used to visualize the data sets in post processing. The use of calibration "dotcards" was investigated to correct for camera perspective and lens distortions in the PLIF images. Lessons learned and recommendations for future experiments are discussed.

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Planar laser-induced fluorescence was used to visualize the reaction-control system jet flow emanating from the aft body of an Apollo-geometry capsule test article in NASA Langley Research Center's 31 in. Mach 10 Tunnel. The reaction-control system jet was oriented normal to the aft surface of the model and had a nominal Mach number of 2.94. The composition of the jet gas by mass was 95% nitrogen (N 2 ) and 5% nitric oxide (NO). The reaction-control system jet flow rate varied between 0 and 0.5 standard liters per minute, and the angle of attack and tunnel stagnation pressure were also varied. Planar laser-induced fluorescence was used to excite the NO molecules for flow visualization. These flow visualization images were processed to determine the trajectory and to quantify the flapping of the reaction-control system jet. The jet flapping, measured by the standard deviation of the jet centerline position, was as large as 0.9 mm, whereas the jet was 1.5-4 mm in diameter (full width at half-maximum). Schlieren flow visualization images were obtained for comparison with the planar laser-induced fluorescence. Surface pressures were also measured and presented. Virtual diagnostics interface technology, developed at NASA Langley Research Center, was used to superimpose and visualize the data sets. The measurements demonstrate some of the capabilities of the planar laser-induced fluorescence method and provide a test case for computational fluid dynamics validation. Nomenclature C p = pressure coefficient P o = tunnel stagnation pressure P 1 = freestream static pressure q 1 = dynamic pressure