GALCIT Home Page
| Fluids Seminar Page |
Graduate Aeronautical Laboratories
Caltech
Abstract-
The problem of a self-sustaining detonation wave diffracting from
confinement into an unconfined space through an abrupt area change is
primarily a competition between the geometric scale of the confinement
and the reaction scale of the detonation. Previous investigations have
shown that this expansion associated with a detonation transitioning
from planar to spherical geometry can result in two possible outcomes
depending upon the combustible mixture composition, initial
thermodynamic state, and confining geometry. The subcritical case is
characterized by the rate of expansion exceeding the energy release
rate. As the chemical reactions are quenched, the shock wave decouples
from the reaction zone and rapidly decays. The energy release rate
dominates the expansion rate in the supercritical case, maintaining the
coupling between the shock and reaction zone which permits successful
transition across the area change. A critical diffraction model has
been developed in the present research effort from which the initial
conditions separating the subcritical and supercritical cases can be
analytically determined. Chemical equilibrium calculations and
detonation simulations with validated detailed reaction mechanisms
provide the model input parameters. Experiments over a wide range of
initial conditions with single and multi-sequence shadowgraphy and
digital chemiluminescence imaging support the model derivation and
numerical calculations. Good agreement has been obtained between the
critical diffraction model and experimental results.
|
GALCIT Home Page
|
|