Showing papers on "Rarefaction published in 1973"

Measurement of elastic velocities of MgO under shock compression to 500 kilobars

Abstract: The velocities of rarefaction waves in shock-compressed MgO have been measured by observing the reduction of the shock front velocity near the sample edges due to the rarefaction waves propagating from the edges. The extent of this ‘edge effect’ is difficult to determine accurately because of its emergent nature. Arrangements sensitive to differences in shock front velocity yielded rarefaction wave velocities close to predicted longitudinal velocities in the high-pressure shock state. Velocities closer to the hydrodynamic sound speed in the shock state were obtained from less sensitive arrangements. These results can be interpreted in terms of a two-stage elastoplastic model of the decompression. The longitudinal velocities measured in shock states up to 528 kb imply second pressure derivatives of the elastic moduli c_(ij)″, given by K_0c_(ij)″ = −1 ± 15, where K is the bulk modulus.

Experiments on Ion-Acoustic Solitary Waves

Abstract: Ion‐acoustic solitary wave (solitons) have been studied experimentally by employing a double‐plasma device. The solitary waves are found to be produced from both a single compressional pulse and a continuous wave. A rarefaction pulse also produces solitons if the pulse width is sufficiently wide. A theory based on the Schrodinger equation accounts for the number of solitons. Recurrence to the original state is observed when a continuous wave is launched. A simple wave‐wave coupling analysis for the recurrence of the original state is given.

Ion rarefaction waves in cylindrical and spherical geometries

Abstract: A similarity technique is used to solve the problem of the ion rarefaction wave associated with a sheath growing at constant speed from a cylindrical or spherical probe into an infinite plasma.

A study of the global solutions for quasi-linear hyperbolic systems of conservation laws

Abstract: The present paper is divided into two parts. In Part 1 we deal with a special initial value problem of the gas dynamics system with initial values more general than those in [6]. In this paper we shall prove the existence theorem in the large, the invariability with respeet to t of the properties of the initial values. Moreover, we have studied some properties of the solutions. For example, suppose that the Riemann problem with initial values (u_0(±∞), v_0(±∞)) contains a forward shock wave, then the solution must contain a forward shock wave. The interactions of the shock and rarefaction wave of the same direction are special eases of our initial value problems. In Part 2 we extend the main results of Part 1 to the systems studied in [7].

Why Syrovatskii's mechanism of dynamic dissipation of magnetic fields does not work

Abstract: Syrovatskii's mechanism of ‘dynamic dissipation of magnetic field’ is reinvestigated. In order to have this kind of ‘dynamic dissipation’ at a neutral line the ratio of current density to particle density must exceed a certain critical value. For conditions in the solar atmosphere near sunspots, this value can only be reached by a mechanism which produces a very large compression of the magnetic field as well as an extreme rarefaction of the density. Syrovatskii claims that his mechanism provides both these features. His enormous field compression, however, can only be obtained if one neglects the restoring Lorentz force (e.g. in Syrovatskii's model the compressed field near the neutral line is about one order of magnitude larger than the field of the sunspots which generates it). The second effect, i.e. the large plasma rarefaction around the neutral line, also is not real. This rarefaction is due to the particular flow field of Syrovatskii's model which allows for a free reconnection of the field lines across the neutral line; the magnetic field is treated like a vacuum field, the effects of the field accumulation near the neutral line being neglected. The aim of the present paper is to show how more realistic models modify Syrovatskii's results. Our numerical calculations lead to a maximum current to density ratio which is a factor of 106 smaller than the one obtained by Syrovatskii. Therefore one has to conclude that in the solar atmosphere one cannot produce in the way described by Syrovatskii the configurations which are necessary for ‘dynamic dissipation’.

Theoretical and experimental investigation of condensation in a centered rarefaction wave

Abstract: The analysis of the process of spontaneous condensation in one-dimensional formulation is dealt with adequately in many papers. However, in reality supersonic flows are not one-dimensional. The most striking effect of two-dimensionality is manifested in two-phase flows, for example in nozzles, inclined sections of jet turbine grills and rarefaction waves. The investigation of these flows, both in the experimental and theoretical aspect, is a complex problem for which a solution has been found only recently. The results are given in this paper of a theoretical and experimental investigation of spontaneous condensation of water vapor in a centered rarefaction wave formed by flow around a protuberant angle by a hypersonic stream.

Nonlinear interaction of a fast magnetogasdynamic shock with a tangential discontinuity

Abstract: A basic problem, which is of considerable interest in geoastrophysical applications of magnetogasdynamics, is the nonlinear interaction of a fast shock (S sub f) with a tangential discontinuity (T). The problem is treated for an arbitrary S sub f interacting with an arbitrary T under the assumption that in the frame of reference in which S sub f and T are at rest, the flow is superfast on both sides of T, and that a steady flow develops. As a result of the nonlinear analysis a flow pattern is obtained consisting of the incident discontinuities S sub f 1 and T2 and a transmitted fast shock S sub f 3, the modified tangential discontinuity T4 and a reflected fast shock S sub f 5 or fast rarefaction wave R sub f 5. The results are discussed in terms of seven significant similarity parameters. In addition special cases like changes in magnetic field direction only, changes in desnity or velocity shear only etc. are discussed.

Dynamical evolution of an expanding gas cloud

Abstract: Riemann's theory of supersonic flow is employed to determine explicitly the various rarefaction and compression waves formed in the course of the expansion of a one-dimensional extended gas cloud into its ambient medium. It is shown that, in most cases, the retarding effect of the ambient medium will result in the formation of a shock wave within the cloud which is responsible for the cloud's final dispersal; the time and the position of the formation of this shock are specified. It is further shown how the various evolutionary features of the expanding cloud--such as its density distribution at different stages of expansion, its lifetime, and its final extent--depend on the initial parameters of the problem. (auth)

Shock-induced turbulent boundary layers

Abstract: Experimental data for an incompressible turbulent moving surface boundary layer are reviewed and a theoretical extension of their predictions is suggested for the case of finite free stream velocities. It is argued that such a boundary layer provides an incompressible analogue for shock-induced turbulent boundary layers. Coles's transformation is used to predict the behaviour of the shock-induced case from the incompressible analogue. These predictions are used to attempt to correlate the available experimental shock-induced turbulent boundary layer data. It is felt that the correlations are reasonably successful for some of the data. It is suggested that the remaining data have been affected by the premature arrival of the contact region and reflected rarefaction wave.

High Reynolds number experimental data for forebody axial force.

Abstract: Brief review of the operational principle and capability of the high-Reynolds-number wind tunnel developed over the last few years. Its test medium is stored in a Ludwieg tube and held there by means of a diaphragm. When the diaphragm is broken, a rearward-facing centered rarefaction fan propagates upstream through the test section and nozzle into the supply tube, and the useful run time is bounded by the reflected rarefaction wave and the starting shock wave caused by choking at the nozzle. The operating problems center around the ability of model and sting support systems to withstand the loads and to meet the instrumentation requirements. Evaluation tests have shown that satisfactory force and moment measurements can be obtained in this facility.

Unsteady-state rarefaction flows with symmetry

Abstract: The article considers unsteady-state isentropic rarefaction flows having either axial or central symmetry. Using the canonical form for writing the relationships which are satisfied along the characteristics, it is shown that, under determined conditions, rarefaction flows may contain a characteristic along which the velocity and the speed of sound vary as in a flow from some stationary source.