High speed gas flows in explosions of cavitated explosives

A possibility of attaining steady flow of detonation products with specific energy much larger than the specific chemical energy of explosive is demonstrated in the case when a cylindrical charge of explosive is fitted with an evacuated cavity. Simple estimates and results of numerical analysis of the process are presented. Steady process may be considered to occur under the following assumptions: (1) effects arising due to jet interaction with cavity walls are negligible; (2) the detonation process is steady. In the case of limited explosive lengths these assumptions have been shown to be correct.When the cavity is filled with gas or liquid, a variety of steady and non-steady flow regimes is possible, depending on the density of the filling medium. One well-known case is that of flow with irregular reflection of shock waves at the cavity axis accompanied with the formation of Mach intersections. Another interesting flow regime is observed to occur in the case of low density filling medium (liquid hydrogen, for example). In this case the filling medium is driven by a “detonation piston” at constant velocity, equal to the velocity of detonation, forming a uniform growing column of hot shock-compressed matter, specific energy of which exceeds by one order of magnitude the specific energy of the explosive. Obviously, the walls of the vessel containing hydrogen must be able to withstand radial loads for a sufficiently long time (20 μ sec).The relative merits of these methods in comparison to others in high speed gas-dynamics is discussed.     

Cylindrical heterogeneous detonation waves

Further experimental studies of blast wave initiated cylindrical heterogeneous (liquid fuel drops, gas oxidizer) detonation waves are described. A pie-shaped shock tube, used for these studies, was altered in certain ways so as to improve the modeling of cylindrical waves. These modifications, along with some operational aspects, are briefly discussed. The breech of the facility, where the blast wave is generated by an explosive, became distorted with usage. Results are presented which show that lower detonation velocities are realized with the damaged breech (other conditions being the same). A photographic and pressure switch wave time of arrival study was made to ascertain the wave shape. Photographs are shown which show that the waves, blast as well as detonation, are close to cylindrical. However, in some cases there is appreciable distortion of the wave front by debris ahead of the wave. Presumably this debris comes from the blasting cap used to ignite the condensed explosive. A series of experiments was conducted using kerosene drops of 388 μm diameter dispersed in air through use of a large number of hypodermic needles. Radial fuel void regions were established by cutting off the fuel flow to a number of needles. Preliminary results relating to the effect of the size of the cloud gap on detonation velocity, quenching, and the initiator energy levels required for detonation are discussed.     

Initiation of spherical detonation in hydrocarbon/air mixtures

Spherical detonations have been initiated by solid explosive (Tetryl) charges in well-mixed stoicheiometric air mixtures with each of the hydrocarbons, ethane, propane, n-butane, isobutane and ethylene at atmospheric pressure. Prior to initiation, the gases were contained in plastic bags; total gas volume and available path length were up to 1.6 m³ and 2 m, respectively. The detonations were shown to be self-sustained by continuous measurement of detonation velocity using X-band microwave interferometry. Measured detonation velocities were in all cases close to calculated C-J values.In a few experiments close to the limits of detonability, velocity and blast pressure/time records indicated that the propagating wave system is sometimes irregular. The irregularity that occurs just after initiation is characterised by a reaction front velocity very much lower than the constant detonation velocity, but subsequently attaining the latter by an acceleration process. These observations indicate the existence of a dissociated phase in which shock and reaction fronts may no longer be coupled.Because similar experimental conditions were used throughout, it was possible to establish the relative susceptibilities of the various fuel gases to detonation. Comparison is made with the Zeldovich criterion and a detonation kernel theory of Lee.     

Shock waves in water foams

Propagation of shock waves in tubes filled with water foams is studied using pressure gauges. Low amplitude shock waves consist of a precursor which propagates at a velocity slightly less than the acoustic velocity in the gas, and of a main compression wave which propagates slower than the precursor. Stronger shock waves have a single front. Maximum pressure rise in the incident and reflected shock waves cannot be calculated using one-dimensional conservation equations at the shock front. It is suggested that the flow of the liquid in foam cells has to be taken into account in order to predict the behavior of shock waves in foams. The nature of the gas which fills the cells is shown to have a strong effect on the quenching of blast waves in foams.     

高超声速化学平衡流辐射流场数值解

本文用数值方法研究了高超声速大钝头体绕流辐射流场。采用粘性激波层控制方程和平衡化学反应气体模型。辐射部份包括连续辐射和线辐射。采用切平板辐射输运模型解决了空间推进的问题，计算结果表明：辐射传热与飞行器再入飞行速度，高度及头部半径密切相关，在计算的条件下，当再入速度小于７．６公里／秒时，辐射传热的影响可以忽略，当再入速度为１１公里／秒左右时，辐射传热可以与对流传热相比拟。当再入速度更大时，辐射传热远     

Prediction of the consequences of a high-velocity collision between meteoric particles and elements of a titanium alloy protective structure

Calculation-experimental studies of a high-velocity collision between VT1-0 titanium plates and ultrafine- and coarse-grained structures with a steel spherical impactor are illustrated. Fine-grained VT1-0 titanium plate samples have been obtained using the abc pressing method. Ballistic measurements have been performed using a 30-mm smooth-bore ballistic installation at velocities of about 2500 m/s. A high-velocity collision has been calculated in the scope of an elastoplastic model of interacting materials with regard to destruction and a different phase state at velocities reaching 15 km/s. It has been indicated that the mechanical properties of the VT1-0 alloy are improved when proceeding from a coarse-grained structure to an ultrafine- grained structure; however, in this case, the result of shock loading is hardly affected in the considered velocity range. Titanium plates can be used as screens to protect the main structure of the aircraft from a high-velocity collision.     

用拉氏量计和分析技术研究固体推进剂冲击波作用过程

本文建立了适合于研究固体推进剂冲击波作用过程的拉氏量计和分析技术,应用这种技术能清楚地表现固体推进剂内部状态变化过程和化学反应过程。并用这种技术研究了聚硫复合推进剂、丁羟复合推进剂、双基推进剂和改性双基推进剂冲击波转爆轰和爆轰过程。结果表明,复合推进剂与双基和改性双基推进具有明显不同的状态变化过程和化学反应过程。     

Moving of a blunt body through the dense atmosphere under conditions of severe aerodynamic heating and ablation

Consideration is given for radiative-convective heat transfer in the vicinity of stagnation streamline in the bow shock layer of blunt body moving through the dense atmosphere at velocities up to 50 km/sec. It is shown that radiative fluxes on non-ablating body surface are subjected to an approximate similarity relations.The effects of gaseous ablation layer on radiative fluxes reaching the body surface is investigated. The results obtained are used to treat the available data on trajectories and light curves of bright fireballs.The treatment procedure proposed is shown to provide reliable estimates of the major meteorite parameters such as their mass, density and size.     

前向空腔的弓形激波特性研究

在FD-14A激波风洞中Ma=10流场对前向空腔构型开展试验研究,应用高速阴影技术捕捉弓形激波的平均位置及振荡幅值,利用压力传感器测量空腔底部的脉动压力。在现有无空腔钝头体激波脱体距离预测方法的基础上发展了前向空腔构型的激波脱体距离预测方法,结合国外的试验测量结果与Organ-pipe理论,验证了这种方法的有效性和适用性,且该方法对激波脱体距离的预测结果与FD-14A风洞试验结果一致。此外,基于这种方法讨论了空腔振荡频率预测方法存在的争议。最后,研究了Ma=10流场下球锥体-前向空腔构型的脱体激波振荡幅值与平均速度的规律。     

The failure of marginal detonations in expanding channels

Critical conditions for detonation failure due to tube expansion have been observed in marginal detonations propagating in a in. (6.35 × 76.2 mm) channel. In these experiments, a well established marginal detonation propagating in the narrow channel entered a test section in which one of the narrow walls was inclined to the central axis at positive angles which ranged from 10° to 45°. Experiments were performed at pressures ranging from 60 to 200 torr (8 to 26.7 kPa) in stoichiometric hydrogen-oxygen mixtures diluted with 20, 50 and 70% argon. Smoke track records obtained on the surface which is the major dimension of the tube, were used to determine failure, incipient failure or self-sustenance of the entering wave.Because of the narrow tube used in the studies the incident waves were marginal in that their velocity was below the expected CJ (Chapman-Jouguet) value, their transverse wave spacing was larger than one would see in a large tube, and the transverse waves were of greater strength than in an ordinary detonation. All of these indicators of marginal behavior became progressively more pronounced as the pressure dropped from 200 torr (26.7 kPa) to the limit pressure of approximately 58 torr (7.73 kPa).The most interesting result of this experimental investigation is that the theoretical analyses predicted that simple one-dimensional opening of the tube should not show a pressure dependence to failure, while the experiments showed a definite decrease in the opening angle required for failure as initial pressure decreased. This behavior is related to the marginality of the incident waves, which is observed to increase smoothly with decreased pressure. It is postulated that detonation failure in the hydrogen-oxygen system occurs when the shock velocity at the end of the cell drops to about 0.60 of the CJ value due either to marginal behavior or to an expansion of the cross section of the tube.     

Numerical validation and parametric investigation on the cold flow field of a typical cavity-based scramjet combustor

The three-dimensional coupled implicit Reynolds Averaged Navier–Stokes (RANS) equations and the two equation standard k–ε turbulence model has been employed to numerically simulate the cold flow field in a typical cavity-based scramjet combustor. The numerical results show reasonable agreement with the schlieren photograph and the pressure distribution available in the open literature. The pressure distribution after the first pressure rise is under-predicted. There are five shock waves existing in the cold flow field of the referenced combustor. The first and second pressure rises on the upper wall of the combustor are predicted accurately with the medium grid. The other three shock waves occur in the core flow of the combustor. The location of the pressure rise due to these three shock waves could not be predicted accurately due to the presence of recirculation zone downstream of the small step. Further, the effect of length-to-depth ratio of the cavity and the back pressure on the wave structure in the combustor has been investigated. The obtained results show that there is an optimal length-to-depth ratio for the cavity to restrict the movement of the shock wave train in the flow field of the scramjet combustor. The low velocity region in the cavity affects the downstream flow field for low back pressure. The intensity of the shock wave generated at the exit of the isolator depends on the back pressure at the exit of the combustor and this in turn affects the pressure distribution on the upper wall of the combustor.     

点式分离火工冲击源仿真分析及载荷形成机理

应用航天器“振源系统-近场结构”一体化建模和分析方法,对点式分离火工冲击源的工作过程进行完整建模和数值仿真分析,提取星箭分离面的力函数。得到了高压气体和爆轰产物在腔体内往复运动、形成爆压双峰的运动规律以及关键结构件在爆压作用下往复运动与其它结构件撞击实现分离解锁的运动规律。在此基础上分析爆压载荷在分离螺母内部的传递机制,得到了星箭界面载荷由爆压载荷以及传递路径上的结构运动、撞击和材料内部压力衰减共同决定的载荷形成机理。     

H2／O2燃烧的超声速非平衡流动的数值模拟

本文从包含组分方程的完全ＮＳ方程出发，采用ＮＮＤ格式和Ｈ２／Ｏ２燃烧模型，通过求解ＮＳ方程，模拟了具有压缩拐角的二维管道和球头两类激波点火、燃烧流动。计算清楚地给出了流场中的激波，爆震波以及各种物理量的分布，并分析了激波、爆震波及其相互之间的合。在此基础上，讨论了稀释剂添加情况对流场的影响。计算中为了解决耦合方程组的刚性，提高计算的稳定时间步长，对化学生成源项，妥善地采用了隐式处理技术。     

Detonation in two-layer systems

Detonation in heterogeneous systems involving parallel layers of two different substances was investigated. It was assumed that the denser medium can undergo fast chemical reaction without mixing with the other medium, and the detonation propagates along the two layers. The process of initiation is associated with a shock wave advancing through the medium of lesser density. An idealized gasdynamic model of the phenomenon is proposed in order to evaluate detonation parameters of the two-layer system on the basis of the characteristic features of its constituents. As calculation shows, in the absence of mixing between the two layers, the detonation is capable of propagating at a higher velocity than in the case when the constituents forming the layers are mixed.     

超声速气流中液体横向射流的气液相互作用过程数值研究

采用Euler-Lagrange方法对来流马赫数为1.94的超声速气流中液体横向射流的气液相互作用过程进行数值研究。计算给出的射流穿透深度、液滴Sauter平均直径(SMD)及液滴速度分布均与实验吻合较好。仿真结果较详细地揭示液体射流喷雾与气流之间的强烈相互作用过程。受液雾影响,射流前形成较强激波,气流依次经过激波及液雾区域,气流速度存在两次下降过程。计算结果揭示,超声速来流可以与射流的液滴轨迹相交,气流经液雾前沿进入液雾区域后,流向往壁面偏折。本文首次发现并提出,由于气液相互作用诱导形成两组反向反转漩涡对,这对于理解两相混合过程具有重要意义。气液相对滑移速度的分析表明,液滴在穿透自由来流并开始转向时受气流作用最为显著,完成转向后气液相互作用逐渐减弱。     

Detonation engine fed by acetylene–oxygen mixture

The advantages of a constant volume combustion cycle as compared to constant pressure combustion in terms of thermodynamic efficiency has focused the search for advanced propulsion on detonation engines. Detonation of acetylene mixed with oxygen in various proportions is studied using mathematical modeling. Simplified kinetics of acetylene burning includes 11 reactions with 9 components. Deflagration to detonation transition (DDT) is obtained in a cylindrical tube with a section of obstacles modeling a Shchelkin spiral; the DDT takes place in this section for a wide range of initial mixture compositions. A modified ka-omega turbulence model is used to simulate flame acceleration in the Shchelkin spiral section of the system. The results of numerical simulations were compared with experiments, which had been performed in the same size detonation chamber and turbulent spiral ring section, and with theoretical data on the Chapman–Jouguet detonation parameters.     

Fine structure of interplanetary shock fronts from the data of the BMSW instrument of the PLASMA-F experiment

The paper is concerned with studying the thickness of fronts of 38 interplanetary shocks detected by the BMSW instrument, which is a part of the scientific payload of the SPEKTR-R spacecraft, which was launched into a highly elliptical orbit in 2011. The main parameters of the interplanetary shocks have been calculated as follows: the ratio of thermal pressure to magnetic pressure before the front β, the angle between the shock front normal and the undisturbed magnetic field θ_Bn, the ratio of the shock propagation velocity to the magnetosonic velocity in the undisturbed region M_ms, and the shock front velocity relative to the Earth. It has been shown that the front thickness determined from the plasma parameters approximately matches the front thickness obtained from the magnetic field measurements and lies between 0.5 and 5 proton inertial lengths. In some events, the oscillations have been observed (upstream and downstream of the shock) in plasma parameters and in the magnetic field data. The length has been found to be between 0.5 and 6 proton inertial lengths for the preceding oscillations and between 0.5 and 10 proton inertial lengths for the following oscillations. The average value of the proton inertial length is 62 km.     

弹丸速度对超爆轰冲压加速器性能影响

为研究超爆轰模态冲压加速器的推进性能,采用混合的Roe/HLL（Harten, Lax, Van Leer）格式,结合自适应网格加密技术(AMR )与沉浸边界法(IBM ),数值模拟了弹丸速度高于预混可燃气体C-J爆速的冲压加速器流场,揭示了弹丸速度对流场结构与推力的影响。结果表明当弹丸速度在一定范围时,斜爆轰波可驻定在弹丸肩部或头部,在弹丸尾部形成高压区加速弹丸,并且,斜爆轰波驻定在弹丸头部推力更高,稳定工作的速度范围 更宽 。     

A numerical study of the charge diameter effect on unsteady detonation

A numerical study for the unsteady detonation of an unconfined tetryl charge of small diameter, which is assumed to be homogeneous, was performed by using the two-dimensional Lagrangian hydrodynamic computer code, 2 DL, with the first order Arrhenius equation of reaction rate. Becker-Kistiakowsky-Wilson (BKW) and Kihara-Hikita (KH) equations of state have been applied to the detonation products.In the case of BKW, it is shown that the rarefaction waves propagating inward from the lateral surface make the reaction rate slow and give a curvature to the front. Then after an induction time, a strong initiation occurs in the reaction zone near the lateral surface and higher pressure zone moves to the axis. This higher pressure accelerates the detonation propagation near the lateral surface and the curvature of detonation front is reduced. Then, the reaction at the lateral surface again begins to decay by the rarefaction waves. Such a sequence of process is repeated periodically.The possibility of the occurrence of the strong initiation depends on the pressure and temperature in the shocked zone near the surface. In a small diameter charge, the delayed explosion becomes weaker near the surface, while its frequency increases. No shock interaction occurs because the direction of the particle flow is always divergent.In the case of KH equation of state, the temperature of detonation is higher than that obtained by BKW and the behaviour of instability becomes rather different from the previous result, i.e. in the axis the pressure oscillates repeating the overdriven and underdriven detonation similar with the case of BKW.     

运载火箭贮箱增压消能器性能仿真与结构方案分析

为了更好地认识液体火箭贮箱增压消能器的工作过程,为消能器的结构方案设计提供支撑,针对典型的锥型和直筒型消能器的结构形式建立仿真模型,使用稳态方法仿真得到气体在消能器内的流场分布情况和消能器内部结构对压力损失和减速效果的影响。根据仿真结果给出消能器结构方案并进行试验,通过试验结果验证了仿真结果的准确性。结果表明：锥型和直筒型消能器的第一层节流结构是造成压力损失的主要部件;对于直筒型消能器,数值仿真的压降大小与试验结果的相对误差为6.3%;入口高速气流直接流经第一层节流结构比先经过扩容再流过第一层节流结构造成的压力损失更大;直筒型消能器的出口面积利用率随着均流筛网距离的增加有着先增加后减小的特点;样条曲线样式的导流锥能提高消能器的出口面积利用率。对贮箱增压消能器内部流场的数值仿真可以为消能器结构设计提供重要依据。