Temperature Measurements by Laser-Induced Fluorescence Spectroscopy in Nonequilibrium High-Enthalpy Flow

Abstract

The e owe eld generated by the high-enthalpy arcjet facility L2K, simulating the stagnation conditions during shuttlereentry and mainly used for testing thermal protection materials, is investigated by using the laser-induced e uorescence (LIF)diagnostictechnique.FortheoperationconditionsoftheL2KfacilityofDLR,thee owconditions are dominated by nonequilibrium effects. In particular, translational and rotational temperatures are assumed to beinequilibrium,butlargedifferencesbetweenrotational,vibrational,and electronictemperatureoccur.Spatially resolved LIF is used to determine rotational and translational temperature of NO molecules and O atoms in the freestream and behind a bow shock upstream of a blunt body. The e ow is modeled numerically using a quasione-dimensional code and a full Navier ‐Stokes two-dimensional axisymmetric code. Good agreement is achieved between the experimental and numerical data in the freestream. The data are also compared with the coherent Stokes anti-Raman scattering measurements performed previously at the same e ow conditions in the same facility on the N2 molecules. Differences caused by the nonequilibrium aspects, in the freestream and across the shock layer, of N2, NO, and O components are evident, and the physical interpretation is discussed.