Energy addition and thermalization issues in a radiatively-driven hypersonic wind tunnel
1995 by Prinmton University. Published by the American Institute of Aeronautics and Astronautics Inc. We present some of the fundamental spectroscopic and dynamic issues relevant to radiative coupling of large amounts of energy into supersonic flow. The work is motivated by the Radiatively-Driven Hypersonic Wind Tunnel (RDHWT) concept, which has been suggested as a possible path to future hypersonic ground test facilities. The RDHWT relies on ultrahigh plenum pressure, followed by downstream radiative energy addition to achieve high Mach number. In particular, we focus on issues of molecular absorption and collisional thermalization in high pressure air at moderate (1,0003,000 K) temperatures. Quantitative models arc developed to predict infrared absorption properties of high-pressure air, including spectral line mixing and collision-induced absorption bands. These models are found to agree well with available experimental data. Microwave absorption spectra, including oxygen resonant absorption at 60 GHz, collision-induced absorption, and absoiption by free electrons are described, and a simple quantitative model is developed. The key pathways for vibrational relaxation of infrared energy are identified, potential rate-controlling processes are revealed, and a simple, single vibrational temperature model is developed.