Rotational relaxation of N2 behind a strong shock wave

Abstract

Using an existing expression for the state-to-state rotational transition rate coefficients, which is derived from the experimental data taken at temperatures equal to or below 1500 K, the master equation for rotational states is integrated with time for N2. The postshock temperature considered is from 400 to 128,000 K. From the numerical solutions of the master equation, the effective collision numbers and characteristic relaxation times are determined. The results show that the effective collision number varies from about 4 at 400 K to about 700 at 128,000 K. The product of the rotational relaxation time and pressure is determined to be 2.47 × 10 -14T1.692 atm s. The calculated rotational relaxation time is larger than the vibrational relaxation time at temperatures above 12,000 K, but is believed to be only hypothetical there because vibration-rotation coupling will pull the temperatures of these two modes together. The present model approximately reproduces the rotational temperature values measured in a shock tube by Sharma and Gillespie and by Fujita et al. up to a postshock temperature of 90,000 K.