Thermal softening of metallic shaped-charge jets formed by the collapse of shaped-charge liners in the presence of a magnetic field

This paper presents an analysis of the possibility of increasing the ultimate stretching and penetration capability of metallic shaped-charge jets in the presence of an axial magnetic field in the shaped-charge liner due to heating and thermal softening of the jet material as a result of a sharp increase in the magnetic-field induction in the jet formation region upon liner collapse. This process is studied by numerical simulation in a quasi-two-dimensional formulation taking into account the inertial stretching of the conductive rigid-plastic rod in the presence of a longitudinal magnetic field in it.     

On the problem of controlling the efficiency of action of shaped-charge jets

It is suggested that noncontact action of a magnetic field on shaped-charge jet elements be used to decrease the penetration depth. A decrease in the depth is attained. A physicomathematical model for the process is constructed that allows one to optimize performance of devices used to realize the action of an external magnetic field. Lykov Academic Scientific Complex “Institute of Heat and Mass Exchange,” Minsk 220072. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 39, No. 3, pp. 36–43, May–June, 1998.     

Use of magnetocumulative generators in experiments on current disruption of shaped-charge jets

Results of experiments on disruption of shaped-charge jets by a pulsed current are reported. An industrially produced helical-coaxial magnetocumulative K-80 generator with transformer energy output was used as a source of energy. The operation of the generator in the experiments performed and the effect of the current-pulse parameters on jet disruption and depth of penetration of a shaped-charge jet into a target are discussed. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 39, No. 3, pp. 30–35, May–June, 1998.     

Behavior of metallic shaped-charge jets with passage of a pulsed electric current through them

The paper reports results of experimental and numerical studies of the disruption of metallic shaped-charge jets by passage of a pulsed electric current through them. Experimental results are presented in the form of x-ray photographs of shaped-charge jets with and without a current and tables of penetration depths in targets. Numerical simulation of the disruption of shaped-charge jets with a current is performed for three possible mechanisms of disruption (development ofMHD instability of shaped-charge jets, volume fracture, and simultaneous development ofMHD instability and volume fracture). Numerical and experimental results are compared. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 41, No. 3, pp. 19–25, May–June, 2000.     

Regularities of the stretching and plastic failure of metal shaped-charge jets

The results of physicomathematical modeling obtained within the framework of continuum mechanics by numerical solution of the two-dimensional axisymmetric nonstationary problem of the dynamic deformation of a compressed elastoplastic bar of variable section are presented. Dependences of the quantitative characteristics of stretching and breakup of a shaped-charge jet (the coefficients of ultimate and inertial elongation and the number of individual elements formed in breakup) on the jet parameters and the jet material properties are revealed by calculations. The calculated dependences are compared with experimental data for plastically failing jets of copper and niobium, and the character of the dependences is explained from the physical viewpoint. Bauman Moscow State Technical University, Moscow 107005. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 40, No. 4, pp. 25–35, July–August, 1999.     

On the possibility of reducing the penetration capability of shaped-charge jets in a magnetic field

The possibility of reducing the penetration capability of shaped charges by producing a magnetic field ahead of the target with flux lines parallel to the charge axis is considered. The problem is studied on the basis of results of experiments in which a magnetic field was produced in a shaped-charge liner before firing, resulting in a sharp reduction or elimination of penetration. The variation of the magnetic induction in the shaped-charge liner moving in the magnetic field is calculated using the model of two conducting coaxial cylindrical shells corresponding to the charge case and liner and assuming constant induction-current density over the shell thickness. A longitudinal magnetic field is specified on the surface of the outer shell as a function of the spatial distribution of the field ahead of the target and the charge velocity. The magnetic-field intensity that can provide a considerable reduction in the penetration capability of shaped charges of various diameters is estimated. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 3, pp. 112–120, May–June, 2007.     

Internal streamwise action of saw-tooth sound waves on turbulent jets

The results of an experimental investigation of the acoustic field produced by turbulent subsonic jets under internal acoustic excitation are presented. It is shown that under the action of saw-tooth finite-amplitude waves the turbulent jets can radiate Mach waves into the ambient medium due to compact acoustic disturbances traveling along the jet at a velocity greater than the speed of sound in the surrounding space.Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 5, 2004, pp. 153–158. Original Russian Text Copyright © 2004 by Pimshtein.     

Effect of energy dissipation on the shaped-charge flow regime

Convergence of a viscous shaped-charge liner to the symmetry axis is described. It is shown that energy dissipation has a significant effect on the process considered. Convergence at small angles can lead to a strong phase explosion of the metastable liquid of the inner, strongly heated, layers of the liner, which is comparable toTNT explosion. An increase in the angle of convergence results in a weak phase “explosion,” which leads to different behavior of shaped-charge jets for different types of linear material. Lavrent'ev Institute of Hydrodynamics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 41, No. 4, pp. 3–11, July–August, 2000.     

Use of an equation describing the transport of the energy of turbulent pulsations to calculate two-phase jets

A finite-difference calculation of an axisymmetric two-phase jet is made on the basis of a turbulence model and an equation describing the transport of the energy of the turbulent pulsations of the carrier phase. The influence of the particles of the disperse phase on the energy of the turbulent pulsations is taken into account.     

Effect of initial heating of the jet-forming layer of shaped-charge liners on the ultimate elongation of jet elements

The functional dependence of the coefficient of ultimate elongation on the temperature of initial heating of the jet-forming layer of shaped-charge liners is obtained. It is established that heating of the shaped-charge liner material before initiation increases the ultimate elongation and, hence, the effectiveness of penetration of plastically fractured, high-gradient, shaped-charge jets.     

Experiments on the formation of a recirculation zone in swirling coaxial jets

 The near flow field of coaxial air jets, with swirl in the outer one, was studied using flow visualization and hot-wire anemometry. The flow is sensitive to both the swirl number and the mass flow ratio between the outer and inner jets. A necessary condition for the formation of an internal recirculation zone (IRZ) is that the swirl number must exceed a minimum value which depends on the mass flow ratio. Spectral analysis of the velocity fluctuations indicates that the formation of an IRZ in the present flow does not appear to be related to the growth of convective flow instabilities. Analysis of the flow visualization and X-wire data indicates that the vorticity dynamics model for vortex breakdown proposed by Brown and Lopez [J Fluid Mech (1990) 222: 553] provides a plausible mechanism for the formation of an IRZ in this flow. Received: 14 June 1999/Accepted: 7 December 1999     

Influence of the initial conditions on axisymmetric jets in a parallel flow

An experimental investigation was made of the initial-section flow of axisymmetric helium, air, and freon-12 jets in a parallel air flow for two different velocity profiles at the nozzle exit near the boundary of the jet. In one case, the velocity profile was determined by boundary layers on the nozzle walls; in the other case, it was produced artificially by means of a honeycomb of tubes of variable length. Measurements were made of the profiles of the mean and the pulsation velocity and the temperature. The flow was also photographed. The investigations showed that, depending on the initial conditions, the intensity of mixing of the jets in the initial section at Reynolds numbers Re 10⁴ (calculated using the jet diameter) can change from the level determined by molecular diffusion to the level characteristic of developed turbulent flow. The flow structure in the annular mixing layer also depends strongly on the initial conditions. The observed ordered structures in the mixing layer are related to a section of development of perturbations near the nozzle. The ordered structures are strongly influenced by the effect on the jet of acoustic vibrations from an external source. When the initial velocity profile is produced by the honeycomb, the transition to developed turbulence may be due to the development of long-wavelength perturbations or to the development of small-scale turbulence generated by the flow over the end of the honeycomb.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 18–24, July–August, 1980.We thank V. M. levlev and K. I. Artamonov for assistance and for discussing the work.