The present work investigates the structure of supersonic turbulent deflagration typically observed as precursors to the onset of detonation. These high-speed flames are obtained after detonation interaction with cylindrical obstacles. Two mixtures having the same propensity for local hot spot generation were used, namely stoichiometric hydrogen-oxygen and methane-oxygen. It was shown that the methane mixture sustained turbulent fast flames, while the hydrogen mixture did not. Three visualization techniques, Schlieren, shadowgraph, and direct chemi-luminescence were implemented to record the evolution of the structure following the detonation interaction with the obstacle. Detailed high-speed visualizations of the nearly two-dimensional flow fields permitted the identification of the key mechanism involved. It was found that the shock reflections in methane permitted strong forward jets behind periodically formed Mach shocks on the front of the deflagration. These hot spots in the re-circulation zones of the jets provided local enhancement of the reactivity through mixing, supporting the formation of new generations of new hot spots. The hot spot formation was identified as the prominent difference between the different mixtures. These reactive pockets further sustained the shock reflection processes. As the methane-oxygen fast flame propagates along the channel, the wave front was observed to organize into fewer modes and eventually led to a reflection capable of the transition to detonation. In the hydrogen mixtures, at similar thermo-chemical parameters, self-sustained fast flames were not observed. Following detonation interaction in the hydrogen mixture, reactive reflections were observed. As the wave propagated downstream after a limited number of reactive reflections, the wave developed a planar wave front and decayed as the reaction zone trailed with an ever-increasing distance. It is postulated that the absence of the forward jets did not allow such fast flames to establish. This jetting slip line instability in methane shock reflections was recently found to be correlated with the low value of the isentropic exponent and its control of Mach shock jetting described by Mach & Radulescu. The lack of the forward jetting of the slip line in the hydrogen mixture with the higher value of the isentropic exponent is in agreement with the Mach & Radulescu.

Indiana University-Purdue University Indianapolis (IUPUI) / Testing of a wave-rotor constant-volume combustor (WRCVC) showed the viability of the application of wave rotors as a pressure gain combustor. The aero-thermal design of the WRCVC rig had originally been performed with a time-dependent, one-dimensional model which applies a single-step reaction model for the combustion process of the air-fuel mixture. That numerical model was validated with experimental data with respect of matching the flame propagation speed and the pressure traces inside the passages of the WRCVC. However, the numerical model utilized a single progress variable representing the air-fuel mixture, which assumes that fuel and air are perfectly mixed with a uniform concentration; thus, limiting the validity of the model. In the present work, a two-step reaction model is implemented in the combustion model with four species variables: fuel, oxidant, intermediate and product. This combustion model is developed for a more detailed representation for the combustion process inside the wave rotor. A two-step reaction model presented a more realistic representation for the stratified air-fuel mixture charges in the WRCVC; additionally it shows more realistic modeling for the partial combustion process for rich fuel-air mixtures. The combustion model also accounts for flammability limits to exert flame extinction for non-flammable mixtures. The combustion model applies the eddy-breakup model where the reaction rate is influenced by the turbulence time scale. The experimental data currently available from the initial testing of the WRCVC rig is utilized to calibrate the model to determine the parameters, which are not directly measured and no directly related practice available in the literature. A prediction of the apparent ignition the location inside the passage is estimated by examination of measurements from the on-rotor instrumentations. The incorporation of circumferential leakage (passage-to-passage), and stand-off ignition models in the numerical model, contributed towards a better match between predictions and experimental data. The thesis also includes a comprehensive discussion of the governing equations used in the numerical model. The predictions from the two-step reaction model are validated using experimental data from the WRCVC for deflagrative combustion tests. The predictions matched the experimental data well. The predicted pressure traces are compared with the experimentally measured pressures in the passages. The flame propagation along the passage is also evaluated with ion probes data and the predicted reaction zone.