Yg. Ju et A. Sasoh, NUMERICAL STUDY OF DETONATION INITIATION BY A SUPERSONIC SPHERE, Transactions of the Japan Society for Aeronautical and Space Sciences, 40(127), 1997, pp. 19-29
Conditions of detonation initiation induced by a supersonic sphere in
a stoichiometric hydrogen/oxygen mixture with 70% argon dilution, are
investigated numerically. The physical model includes a detailed full
chemistry and is solved using an LU-SGS TVD scheme. Transition of the
two extremes, shock induced combustion and detonation, are examined ov
er pressures ranging between 0.2 bar and 10 bar. For shock induced com
bustion regime, the present study exhibits a clear process of coupling
and decoupling between shock wave and combustion wave. For detonation
regime, numerical results yield a propagation velocity of shock wave
within 2% of the theoretical CJ velocity. It is shown that detonation
initiation velocity of the projectile decreases with the increase in p
ressure of the mixture. Moreover, it is found that there is a minimum
initiation velocity on the low pressure side, corresponding to the sec
ond explosion limit of hydrogen/oxygen mixture. Furthermore, autoignit
ion times calculated by two different chemical kinetics also show the
existence of the minimum ignition time. The present analysis exhibits
effects of finite rate chemistry and unsteady process on detonation in
itiation, which is not included in an existing theory. Numerical predi
ctions show a qualitative agreement with experiments, in particular, a
t low pressures.