某成型装药射流的数值模拟与射流转化率

应用LS-DYNA及示踪点处理技术,对某一球锥罩成型装药结构的射流形成过程及射流侵彻靶板过程进行了研究,获得了有效射流沿其运动方向的速度分布、头部速度、侵彻孔几何描述等多项评估射流微元性能的重要参数。计算结果表明,对于普通强度钢质目标靶,在射流侵彻靶板过程中,常规小锥角药型罩产生的有效射流为2000m/s以上的射流段,杆式射流的临界侵彻速度值为1400m/s,从而进一步得到其射流转化率为29.65%。     

线性聚能装药切割岩石的数值模拟

运用改进的MOCL程序,数值模拟了线性聚能装药金属射流的形成以及射流侵彻岩石的全过程,得到了锥角为60°的聚能装药结构爆轰产物膨胀、药型罩变形、射流形成过程及锥角为60°和90°时的射流速度梯变分布。不同时刻射流的分布显示,在拉伸过程中,锥角为60°的聚能射流速度变小,速度梯度较大,头部速度为4500m·s-1;锥角为90°的聚能射流,头部速度为3500m·s-1速度梯度较小,与实际物理过程相一致。结果表明,模拟结果基本符合聚能射流的物理现象和规律,说明采用的物理模型和数值算法是合理的。     

线性聚能装药切割钢靶的数值模拟

基于非线性3D模拟软件ANSYS／LS—DYNA和LS—REPOST,用ALE算法模拟线性聚能装药射流形成以及射流对某均质钢靶切割侵彻的过程。在模拟过程中考虑到射流、空气和钢靶的流固耦合问题,故计算模型基本合理。经过计算,得到了线性聚能装药爆轰波的传播过程、射流形成过程以及钢靶切割过程的3D模拟结果,用LS—REPOST软件也得到了射流头部压力、速度和加速度变化曲线。将数值模拟和计算结果进行对比,结果令人满意、可信,3D数值模拟较以前的2D模拟更形象逼真,显示了ALE算法解决此类问题的优越性。     

间隔靶对射流侵彻能力影响极限的实验研究

利用实验方法对间隔靶影响射流侵彻能力的极限值进行了确定。通过实验，获得间隔靶间隔值与射流侵彻深度的关系曲线，得出间隔靶对射流侵彻能力的降低极限为5．5％左右，即当间隔靶间隔值为最不利于射流侵彻的间隔值时，每个间隙使射流的侵彻能力下降5．5％左右。通过对实验现象的观察，发现射流在间隔靶之间的飞溅是降低射流侵彻能力的一个主要因素。     

一种喇叭-锥角结合药型罩形成射流的数值模拟

为了提高锥角药型罩装药结构的侵彻能力,通过改变其顶部锥角为喇叭形研发了一种新型喇叭-锥角结合药型罩。采用模拟软件ANSYS/LS-DYNA对喇叭-锥角结合药型罩、平顶药型罩、锥角药型罩在爆轰波作用下射流的形成以及对45号钢板的侵彻过程进行数值模拟,并对3种药型罩形成的射流参数如头部速度、射流断裂时间等以及对45号钢板的侵彻性能进行了对比。结果表明,在装药口径为80mm、装药高度为100mm的圆柱和圆锥结合型装药结构的条件下,喇叭-锥角结合药型罩形成的射流头部速度为7 690m/s,比锥角药型罩形成的射流提高约9.54%,对45号钢板的侵彻深度提高约19.82%;比平顶药型罩形成的射流头部速度提高约6.36%,对45号钢板的侵彻深度提高约12.25%。     

一种新型M形顶部结构药型罩的设计及形成射流的侵彻能力分析

在锥角药型罩结构基础上通过改变其顶部结构设计了一种新型M形顶部结构药型罩,并分析了其射流头部的形成机理;采用有限元软件ANSYS/LS-dyna对在爆轰波作用下M形顶部结构药型罩射流的形成过程,以及对45号钢板的侵彻过程进行了数值模拟,并与锥角药型罩、平顶药型罩形成射流的头尾部速度、拉伸长度、杵体大小以及对45号钢板的侵彻能力进行了对比。结果表明,M形顶部结构药型罩的M形顶部结构在爆轰波作用下经二次汇聚形成了射流头部,相同装药条件下,其形成射流的头部速度相比锥角药型罩形成射流的头部速度提高约9.10%,比平顶药型罩形成的射流头部速度提高约5.56%;其侵彻深度比锥角药型罩提高约10.4%,比平顶药型罩提高约7.28%。     

超高性能混凝土梯度材料抗超高速侵彻性能数值模拟EI北大核心CSCD

制备了以不同超高性能混凝土(UHPC)为基础的功能梯度混凝土(FGC)靶,研究了提高混凝土材料抵抗超高速射流的方法,开展了功能梯度混凝土防护工程材料抗超高速侵彻性能实验及数值模拟。通过射流侵彻试验,采集靶体的损伤分布、子弹破碎程度、侵彻破坏深度和破坏形态等各个方面的实验数据,进而分析功能梯度混凝土靶体的抗超高速侵彻性能;采用ANSYS/AUTODYN建立有限元计算模型,并与射流毁伤实验数据对照,验证了模型正确性;利用AUTODYN软件预测了射流和超高速弹体侵彻耦合破坏的结果。结果表明:功能梯度混凝土靶板能够有效阻挡超高速射流侵彻,侵彻深度为241 mm;通过数值模拟对射流形成以及侵彻靶板过程进行了分析并验证其有效性,误差为3.7%。     

药型罩切分方式对射流形成影响的数值模拟

为了研究药型罩切分方式对其形成射流性能的影响,利用数值模拟软件ANSYS/LS-DYNA对横向切分和纵向切分的药型罩以及未切分药型罩在爆轰波作用下形成射流的过程以及对45号板的侵彻能力进行了数值模拟,比较了不同切分方式的药型罩在爆轰波作用下形成射流的形状、头尾部速度、拉伸长度和抗拉伸性能及其对45号钢板的侵彻能力。结果表明,在相同装药条件下,横向切分药型罩相比纵向切分药型罩的头部速度提高约220m/s,且抗拉伸性能更好,对45号钢板的侵彻深度提高约3.26cm;横向切分药型罩相比未切分药型罩的头部速度提高约360m/s,对45号钢板的侵彻能力提高约5.62cm。     

炸高对乳化炸药聚能射流侵彻深度的影响

利用半球型药型罩,对乳化炸药进行聚能装药,讨论了炸高对乳化炸药聚能射流侵彻深度的影响,通过聚能射流侵彻铝板的深度来表征对乳化炸药的侵彻能力,并从机理上进行了分析和讨论,得出在本实验条件下聚能射流的最佳炸高为9 cm左右,这对认识乳化炸药的聚能作用效应具有一定的实际意义。     

起爆方式对线性聚能装药射流形成的影响

以工程中常用的柔性切割器为研究对象,在不考虑端部效应的前提下,对3种起爆方式下线性聚能装药射流的形成过程进行了理论分析和数值模拟。结果表明,不同起爆方式下射流头部速度以端部面起爆最大,线起爆次之,端部点起爆在端面附近处形成的最低,但在距端面一定距离处,射流头部速度又能增大到与端部面起爆的速度相近。在射流内部,端部面起爆形成的射流在内部各点处的速度都是3种起爆方式中最大的,而端部点起爆时,则是随着距起爆点距离的增加由处处小于线起爆的射流速度分布转变到与端部面起爆相同的射流速度分布。在此基础上进一步提出3种起爆方式下线性聚能装药切割目标的数值模拟方法。     

Penetration Cutoff Velocities of Shaped Charge Jets

The maximum depth of penetration, P_max, of a shaped charge jet can theoretically be calculated from 5 quantities for the purely continuous, or for the initially continuous and then particulated, or for the fully particulated penetrating jet. These quantities are the distance Z₀ of the target plate from the virtual origin, the value of γ (i.e. the square root of the ratio of target to jet density), the jet tip velocity v_j,0 the efficient residual velocity v_j,min, and the particulation time t_p. Instead of calculating the individual values of v_j,min for the individual depths of penetration P_exp at various standoff distances, this quantity can quite simply be read from the standoff diagram by means of the penetration cutoff lines- a so-called Standoff/Cutoff-diagram -, using the experimentally determined depth of penetration P_exp. The penetration cutoff lines are lines which start at the virtual origin and which represent the ideal increment in depth of penetration per jet velocity interval in the standoff diagram, the abscissas of this line corresponding to the jet tip velocities. The methods are demonstrated and explained, using the results of three firings with one type of shaped charge as an example. The shots were made at 6, 12, and 24 calibers standoff distance, and the cratering history was also determined in these trials.     

Influence of Drift Velocity and Distance Between Jet Particles on the Penetration Depth of Shaped Charges

The penetration depth of shaped charge jet into target is strongly affected by the stand‐off. The penetration process terminates even when the jet velocity is still high, and the penetration capability of jet particles degrades after jet breakup at a large stand‐off. This work presents an analytical model to describe the radial drift velocity and distance between jet particles, which leads to decreased penetration depth. The results show that jet particles with low drift velocity impact the crater wall easily. Furthermore, the jet particles cannot reach the crater bottom to increase depth because the crater diameter generated by the jet is quite small. Moreover, the distances between jet particles also play an important role in penetration depth under the influences of strain hardening of target, as well as tumbling and dispersion of jet particles. The radial drift velocity and distance between jet particles are investigated by applying the model to non‐precision charge and precision charge penetrations into target at different stand‐offs. The cutoff jet velocity and cutoff penetration velocity also are determined based on the analytical model. With increased stand‐off, the cutoff jet velocity increases, and the cutoff penetration velocity is almost constant. This result is proven by a number of experiments. The stand‐off curves of two charges are also calculated, and results are in good agreement with experiments. The stand‐off curve can be determined with only two or three experiments using the proposed method. Notably, jet particles should have a slow drift velocity and great penetration capability after breakup for suitable shaped charge.     

Calculation of Depth and Crater Diameter for the Supersonic Penetration of Shaped Charge Jet into Concrete

Considering that the sound velocity of concrete is lower than that of metal, this study discusses the effect of stationary shocks and compression during the process of shaped charge jet penetration into concrete when the penetration velocity is greater than sound velocity. The linear relationship between shock velocity and particle velocity is used to describe concrete materials. The state parameters of concrete under shock loading are calculated using Rankine‐Hugoniot jump conditions. Moreover, a combination of these relations with the Bernoulli equation yields a supersonic penetration equation across the shock. A cavity growth equation based on the Szendrei‐Held equation is presented when supersonic penetration occurs. Predictions from the supersonic penetration model are in good agreement with the depth and cavity diameter of experimental results for shaped charge jet penetration into concrete for charge diameters of 60, 142, 200, and 400 mm.     

Turbulent flow study of an isothermal diesel spray injected by a common rail system

The flow characteristics of the intermittent spray of a single-hole diesel nozzle (d_o=0.11 mm) having a 1-spring holder, used in the injection system of heavy-duty diesel engines, were experimentally investigated. The hole belongs to a mini-sac 5-hole nozzle where only on hole is drilled. The mean velocity and turbulent characteristics of the diesel spray injected intermittently by a Common-Rail (CR) system into a pressurized vessel at room temperature were measured by using a 1-D PDPA (phase Doppler particle analyzer). The injection duration was a little stretched out (3 ms) to increase the quasi-steady part of the spray. The axial velocity of the droplets was studied in the main parts of the single-hole nozzle spray, i.e. the leading edge; the central part and the trailing edge. Temporal distributions of the mean axial velocity and its rms were constant in the central spray part, and they showed peaks in the leading edge of the spray. The radial distribution of the normalized axial mean velocity was similar to that of the free gas jet within r/r0.5=1.0−1.5 regardless of time, which is consistent with the theoretical velocity distributions suggested by Hinze. However, in the leading edge near the centreline axis, the normalized axial mean velocity displayed higher values. The turbulence intensity of the axial velocity measured along the radial direction was similar to the free gas jet within r/r0.5=0.5 and higher beyond. However, the turbulence intensity in the leading edge was higher than in the leading edge and the central part within r/r0.5=0.7 where it showed values of the 40–60% of the local mean velocity. The factors of skewness and flatness approached to those of the free gas jet in the central part and the trailing edge. In the leading edge, the flatness factor has presented dispersed values, and the skewness factor was always higher than were those of the two other parts of the spray. The gradient of the half-width exhibited a linear decrease with time since the beginning of the injection to reach the value of 0.106 at the end of the injection. The virtual origin value was within 10–13 mm independently of the injection pressure, and the spray cone angle, determined in comparison to the virtual origin, was close to 30°. The axial decrease of the mean axial velocity showed a great similarity with that of the free gas jet in the central spray part. However, the axial decrease of the rms-velocity was faster than that of the free gas jet.     

CFD simulation of flow pattern and jet penetration depth in gas-fluidized beds with single and double jets

A simple two-fluid model is validated by comparing single-jet fluidization experiments and numerical predictions. Subsequently, flow pattern and jet penetration depth are explored numerically in the bed with double jets under equal and unequal gas velocities. Glass balltoni with a density of 2550 kg/m³ and a diameter of 275 μm is employed as solid phase. The model used in this study considers the effect of the dispersed solid phase on both gas and particle momentum equations of the inviscid model A (Gidaspow, 1994). Numerical simulations are carried out in the platform of CFX 4.4, a commercial CFD code, together with user-defined FORTRAN subroutines. Both jet penetration depth and jet frequency predicted are in good quantitative agreement with measurements in an incipiently fluidized bed with a single jet. By combining solid volume fraction distribution and particle-phase velocity vector profile, three flow patterns (isolated, merged and transitional jets) are identified in the gas-fluidized bed with double jets, which depend more on the nozzle distance than the jet gas velocity. For the equal jet gas velocity, the jet penetration depth decreases with increasing nozzle distance in the merged-jet and transitional-jet regions, then reaches a minimum value in the transitional-jet region, and finally keeps steady in the isolated-jet region. For the unequal jet gas velocity, the merged jet penetration depth increases with increase in the velocity of one jet as the other jet gas velocity is fixed, whilst the jet penetration depths change a little in the transitional-jet region and remain a constant in the isolated-jet region.     

Effect of thrust on supersonic gas jet penetration in gas-solid fluidized beds

Most of the jet penetration studies in gas-solid fluidized beds are for subsonic gas jets, for which many correlations can be found in the literature. In this work, horizontal supersonic gas jets, produced by convergent-divergent nozzles, have been studied, and the intent was to investigate the relationship between the thrust produced by supersonic nozzles and the jet penetration. Different nozzle geometries were used, with three gases having different characteristics (air, helium and carbon dioxide) and at different pressures. All the experimental runs were performed with silica sand particles with the same particle size distribution, and the fluidization velocity was set at a constant value of 0.09 m/s.Jet penetration was measured with a set of triboelectric probes, and it was found that the correlation proposed by Merry, although originally developed for subsonic gas jets, fits really well the experimental results. It was also confirmed that jet penetration displays a strong correlation with the thrust produced by the convergent-divergent nozzles.A correlation originally proposed by Benjelloun's has been modified and the corrected correlation gives the best predictions for gas jet penetration     

The Natural Spread and Tumbling of the Shaped Charge Jet Segments

The collapse mechanism of the shaped charge jet prevents the formation of a jet, the segments of which move in a straight line with absolute accuracy, even under the assumption that the shaped charge is ideally symmetrical. This is a result of the fact that the jet break-up mechanism already starts at the collapse stage, in which the liner material has a big transversal velocity component. A model for calculating the distribution of the angle by which the jet segments' direction of movement deviates from the shaped charge axis of symmetry (the spread angle) is presented in detail. The tumbling frequency of the segments as a function of their velocity and final length is also predicted by the theory. The predictions made by applying the model to the standard 83.8 mm 42 degrees opening angle B.R.L. precision shaped charge were found to be consistent with the data published in open literature. The comparison of these predictions with the data leads also to the conclusion that the cutoff in the copper jet penetration into steel targets occurs when the jet segments start to hit the walls of the already formed hole instead of reaching its bottom without being disturbed on their way.     

不同形状喷嘴的射流流动与卷吸特性

在不同雷诺数下,基于ANSYS Fluent 6.3软件对圆、椭圆、正方、十字、三角5种形状喷嘴的射流卷吸特性进行数值模拟,分析了轴向射流时均速度分布. 结果表明,三角形喷嘴的射流轴向最大时均速度最大,不同形状喷嘴的射流轴向最大时均速度均随轴向位置增大呈幂函数关系衰减;射流穿透深度与雷诺数和弗劳德准数存在多元线性关系;随轴向位置增大,射流横截面形状由初始段内喷嘴形状逐渐向圆形转化并最终扩展为圆形边界;射流轴线速度半值宽随轴向位置增加呈线性增大趋势,三角形喷嘴的卷吸率是十字形喷嘴的1.92~2.32倍.     

Effect of the strain rate on the tensile strength of a copper shaped-charge jet

The data on the penetration depth of a rotating shaped-charge jet were used to estimate the strength of the material of a copper jet formed from a “low” conical linear with an apex angle of120° under the action of centrifugal forces. The estimates0.07–0.15 GPa obtained are close to the static yield point of deformed copper. The jet strength, which is estimated using the length of the fragments formed upon breakup of a rotation-free jet owing to the axial velocity gradient, attains1–1.5 GPa at a strain rate of ≌2·10⁴ sec⁻¹. Lavrent’ev Institute of Hydrodynamics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 1, pp. 111–118, January–February, 1997.