文档介绍：APRIL 1968 TECHNICAL NOTES 765
Rotational Relaxation in Hypersonic
Low-Density Flows
DUVVURI TlRUMALESA*
CETEC Corporation, Mountain View, Calif.
1. Introduction
N recent times e electroth , n beam technique s usei 1 n i d
I measuring the local rotational temperature and gas density
in hypersonic low-density flows of "7 The theory
underlying this measurement is 1) that the ground-state
nitrogen molecule before excitation by beam electrons has a
thermal equilibrium distribution of rotational energy at a
rotational temperature Tr and 2) that the process of excita-
tion of the nitrogen gas by the electron beam and its subse-
quent emission of light due to transitions from upper to lower
rotational levels is related to the initial rotational tempera-
ture and number densities of the nitrogen gas through Muntz
-7 The rotational temperature thus calculated was
always found to be at variance from the translational tem-
perature inferred from other measurements (., impact
pressure). This discrepanc s foun- wa yo occuno t d r fo r Translational Temperature Tt ( K)
flow, s wela 1 s floa l w conditions. e discrepanc2Th "7 e th n yi Fig. 1 Rotational relaxation in freejet expansions-—theory
no-flow experiments is considered to be due to the heating and experiment.
of nitrogen by the electron beam1 or due to the presence of
metastable atoms. r freejeFo 2 t expansions from sonic ori-
fices or in nozzles, this discrepancy is attributed either to where A, w^ are constants. For nitrogen at low tempera-
rotational lag6"8 or to the presence of secondary tures, w% founs nearle i b o dt y
thif o s m Notshoo ai t s e ewi Th that this discrepance b n yca
adequately describe rotationaa y db l relaxation analysis. Rotational relaxation
Under the preceding assumptions, Eqs. (1-4) bined
2. Analysis together and the rotational relaxation Eq. (2) is rewritten as
The analysis will be carrie