External hot surface axisymmetric models for supersonic combustion

An external axisymmetric configuration is introduced for supersonic combustion research in hypersonic wind tunnel flow. In this configuration, high quality data can be generated for validation of computational simulations. The external axisymmetric geometry offers the important advantages of easy optical diagnostic access to the physical fields of interest and a geometry that can be visualised as two dimensional, but is free of non two dimensional edge effects. The application of quantitative OH* measurements in the axisymmetric configuration is introduced in this work. A resistively-heated graphite model with a water cooling system was devised for the axisymmetric arrangement and was commissioned to simulate the hot surface environments typically encountered in hypersonic flight. The model was fueled with pure hydrogen and premixed hydrogen-air mixtures through the fuel delivery system that was constructed for the experimental work. Hot wall temperatures within the range of 1500 to 1800K were achieved during the combustion testing. Several optical techniques were used for the experimental measurements: Two Colour Ratio Pyrometry (TCRP) and Visible near Infrared (VnIR) Spectrometer methods were used for the hot surface temperature measurement; high-speed schlieren was used for the flowfield visualization and an ICCD camera fitted with a narrow-band filter at approximately 310 nm was used for two-dimensional imaging of the OH* chemiluminescence. The TCRP with the wavelength ratio of I(850nm) I(700nm) was used for time-resolved temperature determination of the hot surface. The ICCD camera setup was used to detect and quantify the OH* chemiluminescence. The quantitative chemiluminescence measurements were achieved by using the Abel inversion and a new method which is proposed for the first time in this thesis for the calibration of absolute number density of the radiating OH*. This is a convenient approach when adequate signal magnitudes are emitted from the hot surface radiation and OH* chemiluminescence is acquired through the ICCD device simultaneously during testing. A set of experimental conditions at Mach 2, Mach 4 and Mach 6 flow were examined over a range of total pressure varying from 0.2 MPa to 1.9 MPa and a total temperature of approximately 570K. No evidence of combustion was observed from the ICCD images during the hot surfaces testing at the supersonic and hypersonic conditions. The flow environments produced by the TUSQ facility and the models were evidently not sufficient for ignition. The optical diagnostic techniques developed in this study for external axisymmetric configurations were demonstrated based on combustion results acquired in the nominally quiescent test section environment (without hypersonic flow). These tests indicated that the ignition process was initiated when the background pressure was elevated to about 10 kPa. The combustion flow was reconstructed numerically using a CFD Solver - Eilmer3 with a hydrogen oxidation chemistry model and the addition of a OH* sub-scheme reaction mechanism. The measured peak level of OH* chemiluminescence was over-predicted by the numerical simulation by a factor of about 10. The results of the numerical simulations show that in the supersonic and hypersonic cases, the poor mixing also contributed to suppression of the ignition process