Comparative analysis of internal energy excitation and dissociation of nitrogen predicted by independently developed ab initio potential energy surfaces

In this article we present a comparative atomic level study analyzing the vibrational excitation and dissociation of molecular nitrogen due to ${\mathrm{N}}_2{(}^1{\mathrm{\Sigma }}_g{}^{+})+\text{N}{(}^4{S}_u)$ and ${\mathrm{N}}_2{(}^1{\mathrm{\Sigma }}_g{}^{+})+{\mathrm{N}}_2{(}^1{\mathrm{\Sigma }}_g{}^{+})$ interactions governed by independently developed potential energy surfaces at the University of Minnesota and NASA Ames Research Center. Vibrational excitation was studied for ${\mathrm{N}}_2+{\mathrm{N}}_2$ interactions from $T=10000$ to $25000$ K and for ${\mathrm{N}}_2+\text{N}$ from $T=5000$ to $30000$ K. Nonequilibrium dissociation is studied from $T=10000$ to $30000$ K under the quasi-steady-state condition for ${\mathrm{N}}_2+{\mathrm{N}}_2$ and ${\mathrm{N}}_2+\text{N}$ interactions. Finally, an inviscid Mach 20 dissociating nitrogen flow over a cylinder with a Knudsen number of 0.015 is carried out to study the impact of molecular interactions predicted by independently developed potential energy surfaces on a canonical hypersonic flow.

Figure 1

Example of isothermal relaxation in a box and formation of the QSS for the full nitrogen system (both ${\mathrm{N}}_2+{\mathrm{N}}_2$ and ${\mathrm{N}}_2+\mathrm{N}$ interactions allowed) using the NASA Ames PESs [11, 12].

Figure 2

Characteristics of the QSS at $T=30000$ K, at (a) Vibrational Energy Distribution in QSS, (b) Rotational Energy Distribution in QSS and (c) QSS for various initial internal energy states of the gas.

Figure 3

Characteristic vibrational excitation times for ${\mathrm{N}}_2+{\mathrm{N}}_2$ and ${\mathrm{N}}_2+\mathrm{N}$ interactions.

Figure 4

(a) Dissociation rate coefficients in QSS given by DMS and (b) comparison of DMS-based dissociation rate coefficients and experimental and equilibrium data.

Figure 5

QSS vibrational distribution functions for 0D systems where only ${\mathrm{N}}_2+\mathrm{N}$ or only ${\mathrm{N}}_2+{\mathrm{N}}_2$ interactions are allowed, at (a) $30000$ K, (b) $20000$ K, and (c) $10000$ K.

Figure 6

Composition and temperature history comparison of simulations including both ${\mathrm{N}}_2+\mathrm{N}$ and ${\mathrm{N}}_2+{\mathrm{N}}_2$ interactions using the NASA PESs and the UMN PES, at (a) $T_t=30000$ K, (b) $T_t=20000$ K, and (c) $T_t=10000$ K.

Figure 7

Vibrational energy distribution of ${\mathrm{N}}_2$ molecules in QSS for simulation including both ${\mathrm{N}}_2+\mathrm{N}$ and ${\mathrm{N}}_2+{\mathrm{N}}_2$ interactions, at (a) $T_t=30000$ K, (b) $T_t=20000$ K, and (c) $T_t=10000$ K.

Figure 8

Temperatures and composition of the Mach 20 flow field: (a) translational temperature, (b) rotational temperature, (c) vibrational temperature, and (d) mass fraction of atomic nitrogen..

Figure 9

Temperatures and composition along streamlines shown: (a) temperatures and (b) atomic nitrogen mass fraction and partial density.

Figure 10

(a) Temperature and composition and (b) vibrational distribution functions along stagnation streamline.

Figure 11

(a) Temperature and composition and (b) vibrational distribution functions along the flank of the cylinder.

Figure 12

(a) Temperature and composition and (b) vibrational distribution functions along the aft of the cylinder.