Effect of Initial Disturbance on The Detonation Front Structure of a Narrow Duct

The effect of an initial disturbance on the detonation front structure in a narrow duct is studied by three-dimensional numerical simulation. The numerical method used includes a high resolution fifth-order weighted essentially non-oscillatory scheme for spatial discretization, coupled with a third order total variation diminishing Runge-Kutta time stepping method. Two types of disturbances are used for the initial perturbation. One is a random disturbance which is imposed on the whole area of the detonation front, and the other is a symmetrical disturbance imposed within a band along the diagonal direction on the front. The results show that the two types of disturbances lead to different processes. For the random disturbance, the detonation front evolves into a stable spinning detonation. For the symmetrical diagonal disturbance, the detonation front displays a diagonal pattern at an early stage, but this pattern is unstable. It breaks down after a short while and it finally evolves into a spinning detonation. The spinning detonation structure ultimately formed due to the two types of disturbances is the same. This means that spinning detonation is the most stable mode for the simulated narrow duct. Therefore, in a narrow duct, triggering a spinning detonation can be an effective way to produce a stable detonation as well as to speed up the deflagration to detonation transition process.Comment: 30 pages and 11 figure

Nonlinear relaxation of vibrationally highly excited FREON molecules

We report interferometric studies of nonlinear relaxation processes in vibrationally highly excited CF2Cl2 molecules, present in natural abundance ratio in the three isotropic varieties. The influence of laser frequency and flux, and of the presence of a buffer gas on the time characterizing the relaxation has been established. Our results provide a strong experimental confirmation of the influence that dissociation processes have on the relaxation dynamics. This influence was already clearly established in the case of SF6, with which a comparison is made

Plasma generation in vibrationally nonequilibrium molecular gas flows

Experimental and theoretical studies are made of the associative molecular gas ionization phenomena in N2 and CO under the adiabatic expansion and cooling of a shock-heated gas. It is shown that for a wide range of conditions, the contribution of the associative ionization mechanism substantially exceeds (by several orders of magnitude) the thermal one.L'ionisation associative des molécules N2 et CO en refroidissement adiabatique après chauffage en tube à choc est étudié expérimentalement et théoriquement. On montre que dans un large intervalle de conditions, la contribution des méchanismes d'ionisation associative dépasse considérablement (de plusieurs ordres de grandeur) la contribution thermique