Measuring Nitric Oxide Freestream Velocity Using a Quantum Cascade Laser at CUBRC

velocity measurements. This work reports on freestream velocity measurements for a number of flows for velocities from 2,060 m/s to 5,350 m/s. The measured velocity was compared to facility calculations that are based on the measured shock speed in the driven tube and measured reservoir conditions. The calculations agree with the velocity measurements up to 10 MJ/kg. At higher enthalpies the calculations under predict the actual velocity of the flow. However, the velocity measurement provides a new capability to operate the tunnel in non-tailored mode to obtain velocities greater than 5,300 m/s for at least 2 milliseconds of steady flow. Under most circumstances the LENS I and LENS II shock tunnels produce fully-duplicated conditions for various flight trajectories in the upper atmosphere. At high enthalpy some of the dissociated products are frozen during the expansion into the test section, so non equilibrium chemistry models have been developed to predict the Nitric Oxide (NO) concentration in the free stream gas. Since the presence of this contaminant in the flow changes the nature of the test gas, however slightly, computational fluid dynamic (CFD) calculations are used to compensate for these effects 2 . The actual concentration of the gas must be known. Also it is very desirable to measure the free stream velocity since it is a direct measure of the gas kinetic energy and thus connected to the total enthalpy of the flow, a basic operating parameter of the facility. At CUBRC we have constructed a continuous wave Quantum