Computational study of vibrationally relaxing gas past blunt body in hypersonic flows

Numerical simulations are presented of a steady-state, hypersonic Row over a two-dimensional cylinder of 1 m radius under conditions where the relaxat ion of the vibrational modes is significant. A Mach 6.5 nitrogen flow was s imulated at freestream pressures of 50, 250, and 500 Pa, with a freestream translational temperature of 300 K. Two different freestream vibrational te mperatures, 300 K (causing vibrational heating) and 4000 K (causing vibrati onal cooling) were considered to study the effects on the flowfield. An upw ind-difference numerical scheme was used to solve the inviscid Euler equati ons coupled to the vibrational kinetic models of diatomic nitrogen, assumed as an anharmonic oscillator of 40 quantum levels using two sets of reactio n rates. Comparison with previously reported computations showed a maximum variation of 10% in translational and first-level vibrational temperature a long the surface due to differences in numerical schemes and grid densities ; variation caused hy the two different reaction rate sets was less than 2% . The vibrational cooling case showed a 10% higher shock-standoff distance than the vibrational heating case. The population distribution for the cool ing Ease was non-Boltzmann due to nonresonant energy exchanges in the posts hock region, greater in the shoulder region than in the stagnation region. An increase in freestream pressure for the cooling case increased the shock -standoff distance and non-Boltzmann behavior in the postshock region and n ear the surface. There was, however, a larger equilibrium region in between , in the stagnation region.