Recent Experiments on Hypersonic Combustion in an Expansion Tube Test Facility

The NASA LaRC expansion tube was recommissioned by GASL three years ago for the purpose of conducting hypersonic combustion experiments at Mach 17 total enthalpy in clean air in support of the NASP Technology Maturation Program. The first year of operation was essentially a learning period for development of the test techniques required by this new application of an expansion tube. During the past two years a series of test programs have been conducted which produced reassuring correlations of most experimental observations with CFD calculations, several perplexing data sets that seem at odds with prior observations, and some entirely unexpected difficulties in conducting one set of experiments. The latter are particularly relevant to this workshop since they involve reacting shear layers and detonations. We will briefly review the facility operation, test techniques and certain data sets for which corresponding CFD results are available to establish the basic capabilities and limitations of the facility and confidence in the data. In addition, these data will be used to illustrate some of the fundamental differences between subsonic, supersonic and hypersonic combustion. The focus of the remainder of the discussion will be on the reacting shear layer data and the detonation data. The challenges and opportunities which data from this type of test facility provide for mathematical and/or computational modeling of hypersonic combustion phenomena will hopefully be self-evident. However, we will also indicate a need for more detailed modeling of the facility itself to fully describe the test conditions under which the data is obtained.