Effect of the friction of a thrown piston on the internal ballistics of a one-stage unit

The present article gives a method for the direct measurement of the friction force of cylindrical samples strongly compressed along the axis at the wall of the bore of a gun with a small velocity of the motion, modelling the behavior of a piston in a ballistic unit. As an example, the article gives the results of measurements with a polymer material, i.e., caprolon. On the basis of an experimental investigation, a new friction model is constructed, which is used for the solution of the problem of the internal ballistics of a single stage powder unit with a piston made of caprolon. The laws of similarity of the processes under consideration are investigated. It is established that the value of the maximal pressure of the powder gases and velocity of the piston depend essentially on the value of the friction coefficient.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 76–83, May–June, 1978.     

A ballistic compressor-based experiment for the visualization of liquid propellant jet combustion above 100 MPa

 This paper describes the components and operation of an experimental setup for the visualization of liquid propellant (LP) jet combustion at pressures above 100 MPa. The apparatus consists of an in-line ballistic compressor and LP injector. The ballistic compressor, based on a modified 76 mm gun, provides high-pressure (ca. 55 MPa) clear hot gas for the jet ignition. A piston (projectile) is fired toward a test chamber beyond the barrel’s end, and its rebound is arrested in a transition section that seals the test chamber to the barrel. The LP jet is injected once the piston is restrained, and combustion of the jet further elevates the pressure. At a preset pressure, a disc in the piston ruptures and the combustion gas vents sonically into the barrel. If a monopropellant is used, the jet injection-combustion process then resembles liquid rocket combustion but at very high pressures (ca. 140 MPa). This paper discusses the ballistics of the compression and compares experimental results to those predicted by a numerical model of the apparatus. Experimentally, a pressure of 70 MPa was achieved upon a 12.5 volumetric compression factor by firing a 10 kg piston into 1.04 MPa argon using a charge of 75 g of small-grain M1 propellant. Received: 16 December 1996/Accepted: 15 July 1997     

考虑活塞回复的侧向后喷武器两相流数值模拟

为研究活塞回复运动对火药燃气流动的影响,基于两相流理论对活塞控制侧向后喷武器的发射过程进行了数值模拟研究。考虑控制侧向后喷通道开闭的活塞-弹簧系统的往复运动,建立了结合膛内气固两相流、活塞腔内流固耦合和侧向排气管内气体瞬态流动的武器发射过程数学模型,并将数值模拟结果与相关文献进行了比较验证。得到了该武器发射过程中膛内流场分布与稀疏波传播特性,并与普通武器的膛内流场进行了对比分析。进一步研究了活塞回复运动对火药燃气流动和减后坐效率的影响。结果表明:相对于不考虑活塞的回复运动,在弹丸初速都降低1.52%的情况下,因为活塞回复关闭后喷通道,其减后坐效率由38.86%下降到32.88%,说明在此类武器研究中,不可忽视活塞回复运动。     

Motion of a piston under the influence of gas pressure in the presence of an initial temperature gradient

A study is made of the motion of a piston without initial velocity under the influence of gas pressure. Under the assumption that the temperature gradient is constant and fairly small, expressions are obtained for the distributions of the gas-dynamic parameters in the disturbed region between the piston and the leading edge of the sound wave propagating through the gas at rest.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 177–180, March–April, 1984.     

Experimental investigation of high-speed fluid friction

The experimental investigation of the laws of friction at high relative speeds involves difficulties associated with ensuring that the experimental apparatus provides a sufficiently long slide path. In this paper an automated experimental apparatus is described. This makes it possible to study in a compact fashion the laws of fluid friction at speeds of approximately 150 m/sec under widely variable load and external pressure. The experimental relations for the friction moment coefficient for water in the laminar and turbulent regimes are compared with calculations made by the integral relations method of boundary layer theory. The results of series of experimental and theoretical studies of high-speed friction against ice in the developed fusion layer regime are presented. Questions of the effectiveness of using polymer additives to reduce friction at high speeds are considered. The experimental method described can be used to investigate friction problems involving pastes, emulsions, and other rheologically complex continuous media, in which under conditions of high velocity gradients (strain rates) qualitatively new effects are to be expected.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 3, pp. 74–82, May–June, 1994.     

Plane nonstationary gas flow with a strong discontinuity

The problem of plane, nonstationary gas motion under the effect of a piston in the shape of a dihedral angle moving at constant velocity in the gas is considered. In contrast to one-dimensional motion under the effect of a flat piston, a curvilinear shockwave originates here, and the flow becomes nonisentropic and vortical. This problem is examined herein in a linear formulation when the angle of the piston breakpoint is assumed small. The linear problem reduces to an inhomogeneous Riemann—Hilbert problem whose solution is found explicitly. The problem under consideration adjoins a circle of problems associated with shockwave diffraction and reflection studied by Lighthill [1], Smyrl [2], Ter-Minassiants [3], etc.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 3, pp. 45–50, May–June, 1971.The author is grateful to L. V. Ovsyannikov for interest in the research and useful comments.     

Approximate solution to nonself-similar problem of motion of a piston after an impact

An approximate solution is obtained to the problem of the motion of a piston after an impact and under the influence of gas pressure under the assumption that the parameter = u_o/a _o, where u_o is the initial velocity of the piston anda _o is the velocity of sound in the gas at rest, is small. Functions that determine the law of motion of the piston and the shock wave, and also the gas flow in the disturbed region are found explicitly to terms of order ³ Translated from Izvestiya Akadeinii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 167–171, November–December, 1982.     

Motion of a piston in a cylindrical tunnel with allowance for the additional mass of the gas

We propose to derive relations for the motion of a piston, taking into account the variation of its mass due to the additional mass of the gas entrained by the motion of the piston. We show that the gas entrained by the piston has an appreciable effect on the acceleration of the piston and the acceleration length, with the piston attaining a velocity close to the limiting value.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 167–169, September–October, 1971.     

Unsteady-state flow of a gas in a channel,resulting from the motion of a piston,with magnetohydrodynamic offtake of energy and luminescence of the gas

The present paper discusses the one-dimensional unsteady-state flow of a gas resulting from the motion of a piston in the presence of weak perturbing factors, with which the investigation of the perturbed (with respect to the usual self-similar conditions) motion reduces to the solution of ordinary differential equations, is indicated. The distributions of the parameters of the gas between the piston and the shock wave are found. The conditions under which there is acceleration or slowing down of the shock front are clarified. As an example, this paper considers the unsteady-state motion of a conducting gas in a channel with solid electrodes under conditions where electrical energy is generated, and the flow of a gas taking radiation into account, under the assumption of optical transparency of the medium. The theory developed is used to solve the problem of the motion of a thin wedge with a high supersonic velocity in an external axial magnetic field, taking account of the luminescence of the layer of heated gas between the wedge and the shock wave.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 17–25, September–October, 1970.     

Instability of a spherical gas bubble in a variable-pressure field

Only a few studies, of which we mention [1–5], have been addressed to the problem of the stability of the accelerated motion of a spherical interface of two fluids. In the present paper we consider the problem of the stability of radial motion of the spherical boundary of a gas bubble in an incompressible inviscid liquid under the action of variable external pressure. Surface tension is not taken into account. We study the possibility of the existence of stable motions for broad classes of time dependence of the external pressure, namely for monotonic and periodic dependences. It is shown that stability is possible only for infinitely large bubble radii or for very specific assumptions concerning the initial conditions and the pressure-time dependence law.     

Calculation of hydrogen-air combustion behind detached shock wave for supersonic flow past a sphere

Many of the published theoretical studies of quasi-one-dimensional flows with combustion have been devoted to combustion in a nozzle, wake, or streamtube behind a normal shock wave [1–6].Recently, considerable interest has developed in the study of two-dimensional problems, specifically, the effective combustion of fuel in a supersonic air stream.In connection with experimental studies of the motion of bodies in combustible gas mixtures using ballistic facilities [7–9], the requirement has arisen for computer calculations of two-dimensional supersonic gas flow past bodies in the presence of combustion.In preceding studies [10–12] the present author has solved the steady-state problem under very simple assumptions concerning the structure of the combustion zone in a detonation wave.In the present paper we obtain a numerical solution of the problem of supersonic hydrogen-air flow past a sphere with account for the nonequilibrium nature of eight chemical reactions. The computations encompass only the subsonic and transonic flow regions.The author thanks G. G. Chernyi for valuable comments during discussion of the article.     

Self-similar solution to a problem of axisymmetric motion of gas through a porous medium in the case of a quadratic law of resistance

The results of solution of the self-similar problem of planar flow of gas through a porous medium in the case of a quadratic law of resistance [1] are generalized to the case of axisymmetric motion. The equation in similarity variables for the velocity of isothermal gas flow is reduced to an equation having cylindrical functions as solution. Analytic dependences of the pressure and the gas velocity on the coordinate and time are obtained for a given flow rate of the gas at the coordinate origin and for zero Initial gas pressure in the porous medium.Translated from Izvestlya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza., No. 4, pp. 168–171, July–August, 1982.     

Gas-dynamic calculation of pulsating flow in pipelines

A numerical solution is examined for a system of equations of one-dimensional isothermal flow of a perfect gas in a horizontal pipe with a periodically varying function of the flow rate at the boundary. The numerical solution is compared with the solution of the linearized problem. The results can be used to calculate the pulsating motion of gas in the pipeline systems of piston compressors [1].Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 4, pp. 85–88, July–August, 1972.     

Analytical solutions of one-dimensional problems of gas flow for quadratic resistance law

A study is made of one-dimensional (plane and axisymmetric) problems of the isothermal flow of gas through a porous medium for quadratic resistance law. Self-similar equations for the velocity and pressure of the gas in the porous medium are obtained. Analytical expressions for the pressure and velocity of the gas for constant initial pressure in the medium are obtained. A quadratic dependence of the resistance on the velocity [1,2] is used to describe the motion of the gas in the porous medium at high Reynolds numbers. (Re > 10).Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 73–77, March–April, 1985.     

Turbulent boundary layer with positive pressure gradient on a permeable surface under nonisothermal conditions

It is known that the longitudinal pressure gradient can exert a strong influence on the friction law and the characteristics of a dynamic turbulent boundary layer. The thermal and diffusion boundary layers are more conservative to the effect of the pressure gradient, and, hence, methods of analyzing them are based, in the majority of cases, on the hypothesis of conservativity of the heat- and mass-transfer laws to the longitudinal pressure gradient [1]. This hypothesis is verified by experimental results [2, 3] on heat transfer on an impermeable surface in a turbulent stream with positive pressure gradient under almost isothermal conditions. However, such investigations under nonisothermal conditions are practically nonexistent. An approximate theoretical analysis of the heat transfer in a turbulent boundary layer of a nonisothermal stream with a positive pressure gradient is given in this paper. Experimental results are presented. The experimental investigation was conducted in a burned-out graphite diffuser both with and without injection of an inert gas through the wall.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 43–49, July–August, 1976.     

Instabilities of nonuniform flows of acoustically active media

The analytic methods and results of investigating the acoustic instability of nonuniform steady channel flows are reviewed. The study is based on the system of equations describing the motion of an electrically conducting gas at low magnetic Reynolds numbers [25]. This makes it possible to consider the acoustic effects in plasma and nonconducting gas flows within the framework of a unified approach.Based on paper presented to the fluid mechanics sections of the Seventh Congress on Theoretical and Applied Mechanics, Moscow, August 1991.Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.5, pp. 31–46, September–October, 1992.     

Two-phase couette flow

A study is made of plane laminar Couette flow, in which foreign particles are injected through the upper boundary. The effect of the particles on friction and heat transfer is analyzed on the basis of the equations of two-fluid theory. A two-phase boundary layer on a plate has been considered in [1, 2] with the effect of the particles on the gas flow field neglected. A solution has been obtained in [3] for a laminar boundary layer on a plate with allowance for the dynamic and thermal effects of the particles on the gas parameters. There are also solutions for the case of the impulsive motion of a plate in a two-phase medium [4–6], and local rotation of the particles is taken into account in [5, 6]. The simplest model accounting for the effect of the particles on friction and heat transfer for the general case, when the particles are not in equilibrium with the gas at the outer edge of the boundary layer, is Couette flow. This type of flow with particle injection and a fixed surface has been considered in [7] under the assumptions of constant gas viscosity and the simplest drag and heat-transfer law. A solution for an accelerated Couette flow without particle injection and with a wall has been obtained in [6]. In the present paper fairly general assumptions are used to obtain a numerical solution of the problem of two-phase Couette flow with particle injection, and simple formulas useful for estimating the effect of the particles on friction and heat transfer are also obtained.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 42–46, May–June, 1976.     

Effect of the form of the electrodes on the current distribution in a magnetogasdynamic channel

A solution is given to the plane problem of the flow of a conducting gas across a homogeneous magnetic field in a magnetogasdynamic channel taking account of the Hall effect at small magnetic Reynolds numbers. The channel is formed by two long electrodes, and the cross section of the channel varies slightly and periodically along the gas flow. It is assumed that the electromagnetic forces are small. It is shown that the current distribution in the channel is nonuniform to a consider able degree and that inverse currents can form at the electrodes, with both subsonic and supersonic flows of the conducting gas. Transverse motion of the gas, due to a change in the cross section of the channel, leads to an increase of Joule energy losses. In [1] the current distribution was obtained in a flat channel formed by infinite dielectric walls, with the flow of a steady-state stream of plasma through the channel across a homogeneous magnetic field. With interaction between the flow and the magnetic field, closed current loops develop in the channel.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 26–33, November–December, 1970.     

Acceleration of a gas compressed under conditions of acuteangled geometry

In obtaining high velocities (10–100 km/sec) by methods employing the mechanical motion of compressible media it is customary to use the flow scheme obtained with shaped charges [1–4]. This paper presents the results of a study of an apparatus that can be used to obtain gas jets in the same velocity range but at higher densities by means of a different type of flow.     

The effect of polymer additives on the components of the energy balance of a turbulent flow

On the basis of the experimental data obtained, an analysis is made of the effect of polymer additives directly on the generation of turbulent energy, on the dissipation of the energy of the averaged motion, and on the density of the flux of the kinetic energy of the turbulence. The presence of polymer additives in the turbulent flow significantly changes the relationship between the generation of the turbulent energy and the dissipation of the energy of the averaged motion. Under the action of polymer additives, the density of the flux of kinetic energy decreases over the depth of the channel, which, in turn, brings about a decrease in the influx of energy from the averaged motion to the pulsed motion. The following definitions are adopted below: the x₁ axis of a Cartesian system of coordinates coincides with the horizontal axis of symmetry of the channel and with the direction of the averaged motion of the liquid; the x₂ axis is directed upward; the x₃ axis is perpendicular to the lateral wall of the channel; the origin of coordinates, O, coincides with the lower plane (bottom) of the channel. Further, U₀ is the mean velocity of the flow of liquid in the channel; U_i is the local component of the averaged velocity (i=1, 2, 3); H is the height of the channel; z=2x₂/H; Re is the Reynolds number of the averaged flow;v is the coefficient of kinematic viscosity; u_i is the pulsation component of the velocity (i=1, 2, 3); u_* is rate of dynamic friction; A=(₀–_p0 ^–1 is the coefficient of the lowering of the friction resistance with the flow of polymer solutions; ₀ and _p are the coefficients of the friction resistance with the motion of water and polymer solutions in a channel, respectively; c is the weight concentration of the polymer solution (%); ₀ is the friction stress at the wall; U₊ is the velocity of the flow at the axis of the channel.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 1, pp. 53–58, January–February, 1973.