Post-shock thermochemistry in hypervelocity CO2 and air flow

hypersonic;hypervelocity;high-enthalpy;Mars Science Laboratory;spectroscopy;heat transfer

Sharma, Manu

关键词: hypersonic;    hypervelocity;    high-enthalpy;    Mars Science Laboratory;    spectroscopy;    heat transfer;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/17396/1_Sharma_Manu.pdf?sequence=18&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

This work represents ongoing efforts to study high-enthalpy carbon dioxide flows in anticipation of the upcoming Mars Science Laboratory (MSL) and future missions to the red planet. The work is motivated by observed anomalies between experimental and numerical studies in hypervelocity impulse facilities for high enthalpy carbon dioxide flows. In this work, experiments are conducted in the Hypervelocity Expansion Tube (HET) which, byvirtue of its flow acceleration process, exhibits minimal freestream dissociation in comparison to reflected shock tunnels. This simplifies the comparison with computational result as freestream dissociation and considerable thermochemical excitation can be neglected. Shockshapes of the MSL aeroshell and spherical geometries are compared with numerical simulationsincorporating detailed CO2 thermochemical modeling. The shock stand-off distance has been identified in the past as sensitive to the thermochemical state and as such, is used here as an experimental measurable for comparison with CFD and two different theoreticalmodels. It is seen that models based upon binary scaling assumptions are not applicablefor the low-density, small-scale conditions of the current work. Mars Science Laboratoryshock shapes at zero angle of attack are also in good agreement with available data fromthe LENS X expansion tunnel facility, confi rming results are facility-independent for thesame type of flow acceleration, and indicating that the flow velocity is a suitablefirst-order matching parameter for comparative testing. In an e ffort to address surface chemistry issuesarising from high-enthalpy carbon dioxide ground-test based experiments, spherical stagnationpoint and aeroshell heat transfer distributions are also compared with simulation. Verygood agreement between experiment and CFD is seen for all shock shapes and heat transferdistributions fall within the non-catalytic and super-catalytic solutions.We also examine spatial temperature profiles in the non-equilibrium relaxation region behind a stationary shock wave in a hypervelocity air Mach 7.42 freestream. The normalshock wave is established through a Mach reflection from an opposing wedge arrangement.Schlieren images confirm that the shock con guration is steady and the location is repeatable.Emission spectroscopy is used to identify dissociated species and to make vibrationaltemperature measurements using both the nitric oxide and the hydroxyl radical A-X bandsequences. Temperature measurements are presented at selected locations behind the normalshock. LIFBASE is used as the simulation spectrum software for OH temperature-fitting,however the need to access higher vibrational and rotational levels for NO leads to the useof an in-house developed algorithm. For NO, results demonstrate the contribution of highervibrational and rotational levels to the spectra at the conditions of this study. Very goodagreement is achieved between the experimentally measured NO vibrational temperaturesand calculations performed using an existing state-resolved, three-dimensional forced harmonicoscillator thermochemical model. The measured NO A-X vibrational temperatures are significantly higher than the OH A-X temperatures.