Characterization of Martian Atmosphere Flow Fields in LBK by Laser Induced Fluorescence and Emission Spectroscopy

Abstract

Hygh enthalpy non equilibrium flow fields composed of 97% CO2 and 3% N2 were generated in the arc heated facility LBK in Cologne to simulate heat transfer phenomena in Martian atmosphere. Nitrous oxide mole fractions of about 1% are calculated for the high enthalpy non equilibrium flow fields. One optical experimental technique applied for the flow field characterization in the arc heated facility LBK is emission spectroscopy. This easy to apply line of sight technique is used in LBK for the qualitative determination of the gas composition. A technique with excellent spatial resolution is laser induced fluorescence spectroscopy. LIF on NO was applied to determine rotational temperature profiles in the free stream and in the shock layer of a cylindrical model. Details of the experimental setup and the data reduction procedure are presented. The values of the rotational temperature are compared with results from computational fluid dynamic calculations. The two photon LIF technique on CO is developed for the determination of temperatures with excellent spatial resolution in Martian high enthalpy flow fields. Comparative tests using the TPS basic material SiC were performed in the hypersonic high enthalpy flow field of the arc heated facility L2K for Martian and air atmosphere on a stagnation point model. Gas properties in the flow fields were characterized by emission spectra from the shock region in the wavelength range from 200 to 850 nm in air and Martian atmosphere at comparable gas mass flow rate and reservoir pressure levels. Signals due to NO molecules, N- and O-atoms are present in both Martian and earth like atmospheres, while strong signals due to CN, C2 and C appear only in the spectra with CO2/N2 gas composition. Cold wall heat flux rates were probed using a Heat Flux Microsensor (HFM) based on thermopile technique. Completely different cold wall heat flux rates and surface temperature development on a SiC-probe were measured. Different modes of oxygen atom recombination explain the differences between the two atmospheres.