Advanced model of nitric oxide formation in hypersonic flows

A model for nitric oxide (NO) formation in low-density hypersonic flows is presented. The thermal nonequilibrium reaction rates, reactant energy removal rates, and product energy disposal rates are based on a quasiclassical trajectory analysis of the Zeldovich reactions. At hypersonic flow conditions, the newly obtained reaction rate for the second Zeldovich reaction is approximately an order of magnitude larger than the commonly used rate. The rate of this reaction is a weak function of the reactant internal energy, but it produces vibrationally excited NO molecules that result in an elevated NO vibrational temperature. A flowfield model that includes these effects is proposed, and a computational fluid dynamics method is used to simulate the BSUV1 and BSUV2 flight experiments. The new model generally improves the agreement with the spectrally resolved radiation data; however, it appears that there are additional mechanisms that preferentially remove the highly excited NO molecules.