Expansion Tube Investigation of Shock Stand-Off Distances in High-Enthalpy CO_2 Flow Over Blunt Bodies

摘要

The shock standoff distance in front of a blunt body is sensitive to the thermochemicaludstate of the free stream. Recently, experimental and numerical studiesudhave reported significantly different bow shock profiles in high-enthalpy carbonuddioxide flows, a discrepancy that may result from non-equilibrium processes duringudflow acceleration in ground-based facilities. In this work, an expansion tube is usedudto create a Mach 5.7 carbon dioxide flow, matching the stagnation enthalpy andudthe velocity of previous studies. Images of shock layers are obtained for sphericaludgeometries and a scaled model of the Mars Science Lander. Different sphereuddiameters are used in order to access non-equilibrium and equilibrium stagnationudline shock profiles predicted by theory. Mars Science Lander profiles at zero angleudof attack are in good agreement with available data from the LENS X expansionudtunnel facility, confirming results are facility-independent for the same type of flowudacceleration, and indicating the flow velocity is a suitable first-order matching parameterudfor comparative testing. Heat transfer measurements on the Mars ScienceudLander are also presented for the three different angle of attacks, and the resultsudare consistent with previous studies. Initial results from a proposed organo-metallicudbased emission spectroscopy technique for bow shock layer interrogation are alsoudpresented.