Laser Absorption Spectroscopy Measurements of Air Mass Flow Rate in a Model Scramjet Isolator via Ambient CO 2

This manuscript describes the application of a two-color mid-infrared laser absorption spectroscopy (LAS) diagnostic providing measurements of air temperature, pressure, velocity, and mass flow rate at 300 kHz via ambient CO2. The diagnostic was applied in the isolator of a model scramjet within the University of Virginia Supersonic Combustion Facility (UVASCF). The measurements were achieved by scanning the wavelength of two interband cascade lasers (ICLs) across multiple absorption lines ofCO2 near 2375 and 2384 cm−1. The use of mid-infrared wavelengths provides large absorption signals in air despite the relatively small concentration of CO2. The mass flow rate measurements in the UVASCF isolator agree reasonably well with theoretical predictions over a range of plenum temperatures and pressures, and demonstrate the characterization of internal scramjet flows via flight-capable optical hardware. This is notable compared to our prior measurements acquired behind incident shock waves in a shock tube due to the presence of relatively thick boundary layers (≈1/3 of path length) in the scramjet isolator.