Oxygen atoms' effect on vibrational relaxation of nitrogen in blunt-body flows

Numerical simulations are presented of the steady-state airflow over a hemi sphere cylinder of 1-m radius having hypersonic Mach numbers, where vibrati onal relaxation is the dominant mechanism and the dissociation of oxygen is small. A Mach 6.5 Row was analyzed at freestream pressure of 50 Pa with a nonequilibrium freestream translational temperature of 300 K and vibrationa l temperature of 4000 K; a Mach 1.5 flow was also studied to delineate effe cts of vibration-translation (V-T) energy losses due to N-2-O collisions, T he effects on the vibrational population distribution, temperature, and pre ssure in the flowfield were studied for various media: pure nitrogen and ai r mixtures of 0.0001, 0.1, and 1% oxygen atoms, Code validation was perform ed with previously reported computational results and experimental data for equilibrium Row in freestream, but nonequilibrium in the shock layer, An u pwind difference numerical scheme was used to solve the inviscid Euler equa tions coupled to a vibrational kinetics model of N-2, assumed as an anharmo nic oscillator of 40 quantum levels. The shock-standoff distance comparison with experimental data for a Mach 7.7 and 8.6 airflow past a blunt body sh owed good agreement. For the Mach 1.5 flow at nonequilibrium freestream con ditions, the high efficiency of the V-T rates of N-2-O collisions introduce s additional heating in the shock layer for 0.1% and higher atomic oxygen, thus increasing the shock-standoff distance; for the Mach 6.5 flow, a 0.1% atomic oxygen in air decreases the translational temperature in air compare d to that of pure nitrogen in the stagnation region.