Showing papers on "Rarefaction published in 1998"

Data on Internal Rarefied Gas Flows

Abstract: The present review, containing 178 references, is dedicated to one of the largest and most important branches of the rarefied gas dynamics, namely internal flows. A critical analysis of the corresponding numerical data and analytical results available in the literature was made. The most reliable data were selected and tabulated. The review will be useful as a reference for mathematicians, physicists and aerodynamicists interested in rarefied gas flows. In this paper the complete ranges of the main parameters, determining rarefied gas flows through a capillary, are covered. The capillary length varies from zero, when the capillary degenerates into a thin orifice, to infinity when the end effects can be neglected. The Knudsen number, characterizing the gas rarefaction, varies from zero when the gas is considered as a continuous medium to infinity when the intermolecular collisions can be discounted. The pressure and temperature drops on the capillary ends vary from the small values when the linear theory i...

The New Wave in Shock Waves

Abstract: Laser-driven shock waves (0−5 GPa) can be generated at high repetition rates (100/s) using a moderate-energy tabletop picosecond laser system and a multilayered microfabricated shock target array. High spatial resolution is needed to obtain high temporal resolution of the effects of a steeply rising shock front on molecular materials. The needed spatial resolution is obtained using a sandwich arrangement with a thin layer of sample material termed an “optical nanogauge”. Experiments with an anthracene nanogauge show that ultrafast vibrational spectroscopy can be used to determine the shock temperature, pressure, velocity, and shock front rise time. Shock pulses can be generated with rise times <25 ps, which generate irreversible shock compression, and with rise times of a few hundred picoseconds, which generate reversible compression. These pulses, which have a duration of a few nanoseconds, are termed “nanoshock” pulses. Nanoshock pulses produce large-amplitude mechanical perturbations and can initiate a...

Interaction between gas rarefaction and metal ionization in ionized physical vapor deposition

Abstract: The process known as ionized physical vapor deposition, or I-PVD, consists of the physical sputtering of metal atoms into a dense, inert gas plasma, ionization of the sputtered metal atoms, and subsequent deposition of the films from these metal ions. Measurements have shown a decrease in electron temperature coupled with an unexpected decrease in plasma density as a function of increasing metal flux. Recent plasma modeling work has suggested gas rarefaction as the underlying factor in these declines. Measurements of neutral gas density in the plasma region reported here confirm this model and are consistent with earlier studies of sputtered atom induced gas heating and rarefaction.

Shock Waves; Rarefaction Waves; Equations of State

Abstract: In a fluid, gradients in pressure, velocity, and/or temperature will induce motions in the fluid. Energy is transferred within the fluid, and may also be transferred to the materials that surround the fluid. Energy transfer processes include actual motion of the fluid, viscous flow processes, heat conduction, surface tension, diffusion of matter, radiation, etc. One of these processes often dominates the energy transfer, and the others can be neglected. In high-speed flow of compressible fluids, such as that produced by detonating explosives or by high-speed impact, the transfer of energy is almost all by motion of the fluid, with very little influence of viscosity and other mechanisms. In what follows all energy transfer by means other than fluid motion is neglected. A further simplification is to treat solids like aluminum or iron as fluids, with the strength completely neglected. This drastic approximation is also used throughout this chapter, and usually agrees well with experiment.

Determination of nonideal self-sustained detonation regimes of aluminum particles in air

Abstract: A two-velocity two-temperature model of detonation of aluminum particles suspended in oxygen is employed to study the problem of interaction of a plane detonation wave with an adjacent nonequilibrium rarefaction wave formed with instantaneous removal of the sustaining piston. It is confirmed that the Chapman-Jouguet regimes and weak regimes with a supersonic (with respect to the frozen sound velocity) final state are self-sustained. Stable propagation of the structure is shown for the weak regimes with subsonic (with respect to the frozen sound velocity) and supersonic (with respect to the equilibrium sound velocity) final states (which are unstable in a single-velocity approximation). Interaction of an overcompression wave with a rarefaction wave for relaxation-parameter values that fall into the region of existence of Chapman-Jouguet regimes, results in entry into a Chapman-Jouguet regime. A self-sustained regime of weak detonation that corresponds to the given relaxation parameters is realized outside this region.

Diffraction estimate of the critical energy for initiation of gaseous detonation

Abstract: A criterion for the excitation of detonation is proposed: the critical initiation energy equals the work performed by the expanding detonation products along a path length equal to the longitudinal dimension of a cell. The initial radius of the layer is chosen to be equal to the radius of the detonation wave diffracted at 90° edge at the time the axial rarefaction wave converges on the axis of the gaseous charge. Formulas are obtained for estimating the critical energy for initiation of plane, cylindrical, and spherical detonation waves. The calculated values are in good agreement with experiment.

Relaxation and rarefaction effects on shock wave reflections

Abstract: The influence of relaxation associated with the excitation of vibrational degrees of freedom and chemical reactions, and flow rarefaction on the shock wave reflection phenomena in steady flows is studied in the present paper. The main attention is paid to the impact of the change in the relaxation length, which occurs due to changing Mach number, on the angle of transition from regular to Mach reflection and on the Mach stem height. The Direct Simulation Monte Carlo method is used in the computations. The computational results are compared with predictions obtained using an analytical model that takes into account the change in specific heat ratio behind the shock wave. A substantial effect of relaxation and rarefaction on regular and Mach reflections and on the RR—»MR transition angle is shown.

Variety of nonlinear wave-breaking

Abstract: We discuss the formation of typical (structurally stable) singularities in nonlinear wave breaking in stable and unstable media. The wake wave-break due to the inhomogeneity of the Langmuir frequency is accompanied by electron injection into the acceleration phase. In a wake wave excited behind a finite width laser pulse, the wave-breaking mechanism involves the increase, with the distance behind the pulse, of the curvature of the wake front, followed by the self-intersection of the electron trajectories. In the long wavelength limit, the Weibel instability which leads to the generation of a strong magnetic field, the relativistic self focusing and the Rayleigh–Taylor instability of a thin plasma slab provide examples of a common behavior with the rarefaction wave-breaking in unstable media. We present a solution of the Cauchy problem that describes the evolution of nonlinear perturbations of the Rayleigh–Taylor instability in terms of analytical functions of a complex variable.

Ultra-Thin Gas Squeeze Film Characteristics for Infinitely Large Squeeze Number

Abstract: In this study, the characteristics of ultra-thin gas films are analyzed asymptotically for infinite squeeze number using the molecular gas film lubrication equation with coupled roughness and rarefaction effects taken into consideration. The governing equation of the internal region was obtained by a time averaged technique, and the boundary conditions were obtained numerically from the matching conditions near the boundaries. Two new functions, A and H -1 , were proposed for deriving the matching equation near the boundary. Finally, the characteristics of squeeze film bearings with infinite width were analyzed for various roughness parameters (Peklenik number, standard deviations of the composite roughness, and roughness orientation angles), rarefaction parameter (Knudsen number), and operation conditions (excursion ratio).

Shock Wave Attenuation in Basalt

Abstract: Shock compression experiments on Kinosaki basalt (2. 7 g/cm3) was carried out in the interest of collisional phenomena of planetesimals in the early solar nebula. Shock wave attenuation in basalt were examined using in-material manganin and carbon pressure gauge. The shock waves of 7 and 33 GPa in peak pressure attenuated with the attenuation rate of -1. 8 and -1. 6, respectively. Three attenuation effects were considered: rarefaction wave effect, geometrical expansion effect, and energy dissipation effect. In the rarefaction effect, two waves, reflected wave and edge wave, were newly considered. Our result showed that the reflected rarefaction wave and the geometrical expansion effects affected on shock pressure attenuation and that the energy dissipation effect could be regarded negligible small. The attenuation rate was consistent with that of the impact fragment ejection velocity.

Structure of Shock Waves

Abstract: Shock waves are treated as singular surfaces in gas dynamics, i.E. as abrupt jumps of the thermodynamic fields. Experiments show, however that the thermodynamic fields are smooth in a shock, although quite steep. Thus the pressure may increase by a large factor on the short distance of a few mean free paths. The purpose of this chapter is the calculation of shock structure, that is to say the calculation of the thermodynamic fields across the shock in monatomic gases.

Dsmc法による超音速希薄自由噴流の分子シミュレーション 〔流体工学, 流体機械〕

Abstract: The direct simulation Monte Carlo (DSMC) method is applied to the study of supersonic jets through a thin circular orifice. Effects of roughness of the cell network and the number of molecules in a cell to the simulation result are examined. The structure of the jets can be characterized using the rarefaction parameter introduced by Muntz et al. (AIAA J., 1970). The temperature nonequilibrium between the parallel and the normal direction to the jet axis is reproduced.

A limit theorem for mixing processes subject to rarefaction. II

Abstract: The limit theorem proved in the first part of this paper is applied to the well-known schemes of processes subject to rarefaction arising in queuing theory, mathematical biology, and in problems for counters.

Numerical simulation of plasma-particle interaction in flight under rarefaction and non-equilibrium conditions

Abstract: Summary form only given. The injection of solid powders into thermal plasmas for physical transformation or chemical reaction (spray combustion) has been recognized to offer certain unique advantages. Besides a thorough understanding of transport processes and reaction kinetics under thermal plasma conditions, it is also important to develop the capability of predicting the velocity, temperature, heat flux and the size of a particle during its flight through the plasma to help in the design of a suitable plasma reactor for such applications. A computer code has been developed to simulate the problem, provide such predictions, and to assess the influence of some of the effects encountered in thermal plasma processing operations such as non-equilibrium (two-temperature model), rarefaction (Knudsen effect), and particle charging (individual species heat fluxes).