Oxygen Atoms' Effect on Vibrational Relaxation of Nitrogen in Blunt-Body Flows

Abstract

Numerical simulations are presented of the steady-state aire ow over a hemisphere cylinder of 1-m radius having hypersonic Mach numbers, where vibrational relaxation is the dominant mechanism and the dissociation of oxygen is small. A Mach 6.5 e ow was analyzed at freestream pressure of 50 Pa with a nonequilibrium freestream translational temperature of 300 K and vibrational temperature of 4000 K; a Mach 1.5 e ow was also studied to delineate effects of vibration ‐translation (V‐T)energy losses due to N 2‐O collisions. The effects on the vibrational population distribution, temperature, and pressure in the e owe eld were studied for various media: pure nitrogen and air mixtures of 0.0001, 0.1, and 1% oxygen atoms. Code validation was performed with previously reported computational results and experimental data for equilibrium e ow in freestream, but nonequilibrium in the shock layer. An upwind difference numerical scheme was used to solve the inviscid Euler equations coupled to a vibrational kineticsmodel ofN 2,assumedasananharmonicoscillatorof40quantum levels. Theshock-standoffdistance comparison with experimental data for a Mach 7.7 and 8.6 aire ow past a blunt body showed good agreement. For the Mach 1.5 e ow at nonequilibrium freestream conditions, the high efe ciency of the V ‐T rates of N2‐O collisions introduces additional heating in the shock layer for 0.1% and higher atomic oxygen, thus increasing the shockstandoff distance; for the Mach 6.5 e ow, a 0.1% atomic oxygen in air decreases the translational temperature in air compared to that of pure nitrogen in the stagnation region.