Investigation of certain techniques for stabilizing detonationwaves in a supersonic flow

The salient features of detonation wave propagation in a supersonic flow of a stoichiometric hydrogen-air mixture in plane channels of both constant and variable cross-section are numerically investigated for the purpose of determining the conditions ensuring stabilized detonation. The propagation of a detonation wave formed in a variable-cross-section channel is studied. For different inflow Mach numbers the geometric parameters of a channel providing the detonation combustion stabilization are determined. An investigation of detonation wave stabilization in a supersonic flow of a combustible gas mixture in a plane channel with parallel walls using additional weak discharges is continued. The effects of the flow Mach number, the additional discharge energy, and the discharge location on detonation wave stabilization are studied.     

Distinctive features of galloping detonation in a supersonic combustible-mixture flow under an inert gas layer

The problem of detonation initiation in a supersonic flow of a stoichiometric propane-air mixture occupying partially or completely the cross-section of a plane channel is considered. The initiation in the flow is produced by a step or a wall completely cutting off the flow. The study is conducted within the framework of one-stage combustion kinetics. A numerical method based on the Godunov scheme is employed. The critical conditions for detonation formation are determined in terms of the oncoming flow velocity. A previously unknown mechanism of detonation propagation is found; it is related with the presence of the combustible mixture in the wall layer under an inert gas layer. It is due to the formation of a complicated wave structure of the flow characterized by the penetration of a shock wave formed in the inert gas layer into a combustible mixture layer ahead of the detonation wave with the result that the latter layer is heated and ignited. The process as a whole is periodic in nature, as distinct from the conventional cellular detonation in a homogeneous fluid. Many problems arise in connection with the use of detonation in engines and other power plants. The most important among them are detonation excitation and stabilization in combustion chambers. The detonation initiation within a layer under conditions of unbounded space and a fluid at rest was experimentally investigated in [1]. In the case of a combustion chamber bounded in the transverse direction, some new effects accompanying the detonation might be expected.     

Detonation attenuation by foams and wire meshes lining the walls

In the present study systematic photographic investigations were performed of detonation interactions with foams and wire meshes lining the channel walls. An initial cellular detonation wave was propagating along a damping section (acoustic absorbing walls) which removed the transverse waves associated with its cellular structure. In some cases the wave had failed and a fast deflagration wave (a shock followed by a decoupled flame) was obtained and propagated at about half the C-J detonation speed. The events were studied photographically using a high speed framing camera and smoked foils.     

Generation and stabilization of detonation in a plane elbowed channel

The problem of detonation initiation in a supersonic flow of a stoichiometric propane-air mixture in a plane elbowed channel of constant width is considered. In the bend zone the channel walls are made in the shape of circles of given radii, whose lengths are determined by the given angle of the channel turn. An investigation is performed within the framework of the single-stage combustion kinetics using a numerical method based on the Godunov scheme and included in an original program complex, or a “virtual experimental setup”, developed for performing multiparameter calculations and flow visualization. The critical conditions of detonation generation are determined as functions of the oncoming flow velocity, the channel turn angle and width, and the radii of curvature of the walls.     

Stability of gas mixture flow with a stabilized detonation wave in a plane channel with a constriction

The stability of a flow with a stabilized detonation wave is studied within the framework of a detailed kinetic mechanism of the chemical interaction. The flow is due to the initiation of detonation combustion of a stoichiometric hydrogen-air mixture that enters into a plane channel with a constriction at a supersonic velocity greater than that of the self-sustained detonation propagation. The flow under consideration is numerically investigated using the software package developed by the authors. It is established that the flow formed in the channel, whose geometric parameters ensure the detonation stabilization in the case of the inflow Mach number M₀ = 5.2, is stable against strong disturbances of a certain type. The effect of an increase in the inflow Mach number and the dustiness of the combustible gas mixture entering into the channel on the stabilization of detonation combustion in the flow is investigated.     

Cellular detonations in bidispersed gas-particle mixtures

Formation of cellular detonation in bi-fractional stoichiometric mixtures of aluminum particles and oxygen is investigated numerically. The detonation cell size depends on the particle diameters and relative concentration of the fractions. Certain degeneration of cellular detonation is obtained when compared to the monodisperse mixtures. It is characterized by maximal pressure decrease, transverse wave relaxation and detonation front rectification. Complete degeneration of cellular detonations and stable propagation of a plane detonation front is found in some bi-fractional mixtures. The numerical results are confirmed by acoustic analysis of the detonation structures. This paper is based on work that was presented at the 21st International Colloquium on the Dynamics of Explosions and Reactive Systems, Poitiers, France, July 23–27, 2007.     

Intensification of a detonation wave in the zone of secondary reactions in a two-phase medium

A method is proposed for the numerical calculation of one-dimensional nonsteady-state flows of a mixture of a gas with particles, based on the separation of a system of differential equations for a two-phase medium into two subsystems. The problem is solved concerning the propagation of a plane detonation wave in a mixture of a detonating gas with particles, behind the front of which secondary chemical reactions are taking place between the vapors of the particle material and the detonation products. The velocity profiles of the gas and of the thermodynamic functions behind the detonation wave front are determined, and also the dependence of the detonation velocity on the distance to the point of initiation. The conditions for intensification of the detonation wave are obtained in the zone of secondary reactions.Leningrad. Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 92–96, September–October, 1972.     

Transition of plane overdriven detonation wave to the Chapman-Jouguet regime

The asymptotic laws of behavior for plane, cylindrical, and spherical infinitely thin detonation waves were found in [1, 2] for increasing distance from an igniting source in those cases in which the waves changed into Chapman-Jouguet waves as they decayed. It was shown that the plane overdriven detonation wave approaches the Chapman-Jouguet regime asymptotically, while the transition of the cylindrical or spherical strong detonation wave into the Chapman-Jouguet wave may occur at a finite distance from the initiation source.Similar conclusions are valid for the propagation of stationary steadystate detonation waves which arise with flow of combustible gas mixtures past bodies.However, numerous experiments [3, 4] on firing bodies in a detonating gas show that the overdriven detonation wave which forms ahead of the body decays and decomposes into an ordinary compression shock and a slow combustion front. To establish why the wave does not make the transition to the Chapman-Jouguet regime, in the following we consider the propagation of a plane detonation wave and account for finite chemical reaction rates. We use the very simple two-front model (ordinary shock wave and following flame front). Conditions are found for which transition to the Chapman-Jouguet regime does not occur. We first consider the propagation of an unsteady plane wave and then the steady plane wave. It is found that for all the mixtures used in these experiments transition to the Chapman-Jouguet regime is not possible within the framework of the assumed model.     

周期性非均匀介质中气相爆轰波演变模式研究

气相爆轰波在周期性非均匀介质中的起爆, 稳态传播和失效机制都极为复杂, 很多物理机制尚不明确, 是当前爆轰物理领域研究的热点和难点. 本文使用反应欧拉方程和两步化学反应模型对爆轰波在非均匀介质中的传播机理进行了数值模拟研究, 非均匀性由横向周期性分布的温度扰动体现, 重点分析不同波长、不同幅度的温度扰动对波阵面波系结构的影响. 计算结果表明, ZND爆轰波在温度扰动下向胞格爆轰波的转变主要受制于两种竞争性因素: 一是爆轰波内在的不稳定性; 二是温度扰动的波长和幅度, 前者是内因, 后者是外因. 温度扰动的存在抑制横波的发展, 延迟了ZND爆轰波向胞格爆轰波的演化, 并且内在不稳定性的增加可以减慢这种延迟现象. 这说明, 温度扰动可以在一定的范围内抑制胞格不稳定性的发展, 但是不能够终止这一过程. 温度的不连续性使得爆轰波阵面更为扭曲, 并在横波附近存在较弱的三波点结构, 即温度扰动可增加爆轰波固有的不稳定性, 改变爆轰波阵面的传播机理. 幅值较大的人工温度扰动可抑制爆轰波的传播和爆轰波自身的不稳定性. 爆轰波阵面胞格结构的形成取决于温度扰动与其自身的不稳定性.      

爆轰波在阻尼管道中声吸收的实验研究

实验旨在研究气相爆轰波在阻尼管道 (管壁上衬有吸收材料 )中传播时的衰减现象。先是在光滑管壁的管道中产生稳定的具有胞格结构的爆轰波 ,然后使其通过专门设计的管壁上衬有吸收材料 (金属丝网或不锈钢纤维 )的阻尼段。利用高速摄影、压力传感器和烟迹技术等手段 ,记录和测试了阻尼段对几种混合气体爆轰波的传播速度、爆压及胞格结构产生的影响。实验分别在方管和圆管中进行。发现在某些条件下爆轰波可以被衰减成强爆燃。