Results are presented of numerical simulations of the diffraction which occurs when a detonation propagating through a hydrogen-oxygen mixture in a tube suddenly comes into contact with a bounding hydrogen-oxygen mixture. These simulations are, in part, validated by experimental observations of this diffraction process. The nature of the diffraction which occurs depends on whether the equivalence ratio of the primary mixture in the tube is equal to or greater than the rquivalence ratio of the secondary bounding mixture. When the equivalence ratios are equal the resultant diffraction is identical to that which occurs when a detonation propagates from a tube into a larger bounding region. When the equivalence ratio of the mixture in the tube is greater than that of the bounding mixture the diffraction results in the formation of an oblique shock-oblique detonation complex in the bounding mixture which is identical to that which will occur in oblique detonations generated by a high speed wedge as, for example, in oblique detonation ram jets. The results of experimental studies of these diffraction processes using a layered detonation tube and a laser framing camera are first described. It has been possible to numerically simulate the unsteady diffractions which occur using the Flux Corrected Transport Algorithm together with a simplified two step model of the governing hydrogen-oxygen kinetics. The results of these simulations are presented.
The simulations reproduced the oblique shock/detonation complex observed when the bounding mixture is leaner than that the mixture in the tube. When both mixtures are stoichiometric a key issue is whether the detonation will be re-ignited as it expands into the larger bounding region. Experiments indicate that the cellular structure of the detonation plays a key role in this process and these results are reproduced by the numerical simulations, and in some cases an almost one on one agreement between simulation and experiment has been obtained.
Based on the work of: Dr. E.S. Oran, The Naval Research Laboratory, Dr. David Jones, Aeronautical and Maritime Research Laboratory, Australia, and Dr. N.A. Tonello, The University of Michigan.