Abstract
Numerical simulation of propagation mechanisms of gaseous detonations in the inhomogeneous medium is studied by using the reactive Euler equations coupled with a two-step chemical reaction model. The inhomogeneity is generated by placing artificial temperature perturbations with different wavelengths and amplitudes. The motivation is to investigate the effect of artificial perturbations on the evolution or amplification of cellular instability. The results show that, without artificial perturbations, a planar ZND detonation can evolve into a fully-developed cellular detonation after a distance because of the amplification of the cellular instability. With the artificial perturbations evolved in, at the early stage, the artificial perturbations control the transverse wave spacing by suppressing the amplification of the cellular instability. However, after a steady-state, the cellular instability starts to amplify itself again and eventually transits to a fully-developed cellular detonation. It is demonstrated that the presence of the artificial perturbations delays the formation of the cellular detonation, and the increase of instability factor can slow down this delay. It is also found that, if the wavelength of the artificial perturbations is close to the transverse wave spacing of the cellular detonation in the homogeneous medium, synchronization of these two factors occurs, and hence a cellular detonation with extremely regular cell pattern is immediately formed. The temperature discontinuity causes the front to be more turbulent with the presence of weak triple-wave structure locally besides the natural transverse waves. The artificial perturbations can increase the intrinsic instability, and hence changes the propagation mechanism of the detonation front. In contrast, large artificial perturbations could prohibit the propagation but reduce cellular instability. It is concluded that the competition of artificial perturbations with intrinsic detonation instability dominates the evolution of cellular structures of the detonation front.
Highlights
Gaseous detonation can be used as an efficient propulsion method to serve the design of detonation engines, or it can appear in an industrial explosion accident seriously
As the weak perturbations amplified itself at a rate controlled by the instability factor, a balance will eventually be obtained with the presence of transverse waves with a constant spacing
The results show that, without artificial perturbations, a planar ZND detonation can evolve into a fully developed cellular detonation after a distance because of the amplification of cellular instability on its front
Summary
Gaseous detonation (explosive) can be used as an efficient propulsion method to serve the design of detonation engines, or it can appear in an industrial explosion accident seriously. The wavefront of the detonation wave is twisted, traditionally accompanied by Mach reflection of the detonation wave This gradient distribution model is closer to the real situation, it is not conducive to establishing a steady-state propagation mechanism in non-uniform media. Detonation initiation in inhomogeneous medium has been extensively studied following the temperature gradient ignition theory proposed by Zel’dovich [18] These studies mainly focus on the critical conditions for detonation initiation [19,20], propagation mode [21,22,23], and the effect of the reaction model [24,25,26]. The effects of wavelength and amplitude of the perturbations on the detonation development regime were examined
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