Rotational and Vibrational Temperature and Density Measurements by Planar Laser Induced NO-Fluorescence Spectroscopy in a Nonequilibrium High Enthalpy Flow

Abstract

LIF experiments were performed in the flow field of the high enthalpy facility L2K. This arc heated facility, which is mainly used for testing thermal protection materials, offers a wide choice of flow conditions to simulate the stagnation conditions during shuttle re-entry. The flow conditions are dominated by nonequilibrium effects. For the operation conditions of L2K translational and rotational temperatures are assumed to be in equilibrium, but large differences between rotational, vibrational and electronic temperatures occur. Laser induced fluorescence is used to determine rotational and vibrational temperatures and the density of NO in the free stream and behind a bow shock upstream of a blunt body. The flow is modelled numerically using a quasi 1D-code. Good agreement is achieved between the experimental and numerical data in the free stream. The data are also compared with the CARS measurements performed at the same flow conditions in the same facility. Differences in the free stream vibrational temperature of N2 and NO are due to the faster vibrational relaxation of NO-molecules.