Near-surface CO2 tunable diode laser absorption spectroscopy concentration measurements in the LENS-XX expansion tunnel facility
Weisberger, Joshua Michael
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Measurements of carbon dioxide concentration are made in the LENS-XX expansion tunnel facility at CUBRC to investigate the effects of surface catalysis on vehicles in hypersonic flows. A high-resolution tunable diode laser absorption spectroscopy setup probes the P36e carbon dioxide absorption line of the ν 1 + ν 3 combination band located at 2.7153 μ m (3682.765 cm -1 ). Numerical simulations are computed with DPLR using the specified reaction efficiency surface catalysis model. Absorption measurements adjacent to the surface of a 2 inch diameter, 2.5 inch long aluminum cylinder correlate well with simulations indicating only small amounts of catalytic behavior at the surface. The velocity, density, freestream temperature, specific enthalpy, and stagnation point pitot pressure of the run are 4.6 km/s (M = 7.1), 1.53 g/m 3 , 1328.4 K , 11.75 MJ/kg , and 31.6 kPa , respectively. The simulation of the absorption spectrum is performed using a non-homogeneous line-by-line code utilizing the HITRAN database for spectroscopic parameters. Input data for the line-by-line code is obtained from computational fluid dynamics simulations of both the cylinder and the expansion tunnel facility. Specified reaction efficiency for the mechanism CO + O [arrow right] CO 2 is determined inversely using detailed CFD and comparisons to experimental measurements. The catalysis model specifies a reaction-specific efficiency that determines the fraction of reactants reaching the surface for which a recombination event occurs. Best agreement was found for γco = 0.00025 to 0.0005, indicating that the coupled line-by-line code and CFD approach is useful for assessing near-surface composition using tunable diode laser absorption measurements of hypersonic flows.