Characterization of the NASA Langley Arc Heated Scramjet Test Facility using NO PLIF

Abstract

The nitric oxide planar laser-induced fluorescence (NO PLIF) imaging was used to characterize the air flow of the NASA Langley Arc Heated Scramjet Test Facility (AHSTF) configured with a Mach 6 nozzle. The arc raises the enthalpy of the test gas in AHSTF, producing nitric oxide. Nitric oxide persists as the temperature drops through the nozzle into the test section. NO PLIF was used to qualitatively visualize the flowfield at different experimental conditions, measure the temperature of the gas flow exiting the facility nozzle, and visualize the wave structure downstream of the nozzle at different operating conditions. Uniformity and repeatability of the nozzle flow were assessed. Expansion and compression waves on the free-jet shear layer as the nozzle flow expands into the test section were visualized. The main purpose of these experiments was to assess the uniformity of the NO in the freestream gas for planned experiments, in which NO PLIF will be used for qualitative fuel-mole-fraction sensitive imaging. The shot-to-shot fluctuations in the PLIF signal, caused by variations in the overall laser intensity as well as NO concentration and temperature variations in the flow was 20-25% of the mean signal, as determined by taking the standard deviation of a set of images obtained at constant conditions and dividing by the mean. The fluctuations within individual images, caused by laser sheet spatial variations as well as NO concentration and temperature variations in the flow, were about 28% of the mean in images, determined by taking standard deviation within individual images, dividing by the mean in the same image and averaged over the set of images. Applying an averaged laser sheet intensity correction reduced the within-image intensity fluctuations to about 10% suggesting that the NO concentration is uniform to within 10%. There was no significant difference in flow uniformity between the low and high enthalpy settings. While not strictly quantitative, the temperature maps show qualitative agreement with the computations of the flow.

Comparisons Between NO PLIF Imaging and CFD Simulations of Mixing Flowfields for High-Speed Fuel Injectors

“…Prior to conducting mixing tests, earlier experiments were conducted in the AHSTF with the laser sheet configured to interrogate the flow at the exit of the Mach 6 facility nozzle. 18 These tests confirmed that NO exists in sufficient concentration (i.e., to produce enough fluorescence to detect) and sufficient spatial uniformity for images obtained from the mixing flowfield to be interpreted properly (i.e., concentration of NO proportional to concentration of air). The initial set of mixing tests of the injectors described above has been conducted using only NO PLIF imaging and no intrusive measurements.…”

“…Figures [16][17][18][19][20] show the comparisons between the time-averaged PLIF images and the corresponding computationally derived PLIF, termed CFI, obtained for different fuel injectors and using different sets of LIF transition lines. Figure 16 shows the time-averaged streamwise images obtained along the centerline of the strut injector block and cutting through the middle injector.…”

“…The same cameras, excitation schemes, etc., were used in other past experiments. 18,19 The fluorescence was imaged onto a gated, intensified charge-coupled device (CCD) (Princeton Instruments PIMAX-II R ), and represented using 16-bits of resolution. A single Nikon R UV lens with a focal length of 105 mm and f/4.5 aperture was used.…”

The Versatility of HVOF Burner Rig Testing for Ceramic Matrix Composite Evaluation

“…Adequate testing for these types of conditions is a challenge in and of itself. Current test facilities [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] consist of combustion, arc-plasma, laser or combinations thereof to generate the temperatures, velocities and/or environments of interest (Table 1). Most of these rigs can effectively evaluate two or, at most, three of the above conditions.…”

“…Related to this is the need for diagnostic techniques to measure thermal gradients and local strain as well as health-monitoring techniques to assess the progressive damage that occurs during the test. [3] Jet fuel combustion 0.1 1550 AFIT HVOF [4] Combustion 1 2500 HYMETS [5][6][7] Arc-plasma 5 2480 NASA Combustion Scramjet * [8] Combustion Scramjet 6 1400 NASA Arc-Heated Scramjet * [9][10][11] Arc-heated Scramjet 8 2600 GHIBLI [12] Arc-plasma 10 9700 SCIROCCO * [13][14][15][16] Arc-plasma 12 9700 Pprime MAATRE * [17] Burner Rig 1 1600 VKI Plasmatron * [18] and other plasma [19][20][21] Induction-Plasma 1 11,700 DRL HEG* [22,23] Free-Piston Shock Tunnel 10 1176 * Capable of large specimen size (>250 mm).…”