Showing papers on "Rarefaction published in 1983"

An Experimental Investigation of Molecular Rarefaction Effects in Gas Lubricated Bearings at Ultra-Low Clearances

Abstract: : The experimental investigation discussed here gives experimental confirmation of the slip-flow theory for modeling hydrodynamic gas bearings with clearances below 025 microns An interferometric technique employing two CW lasers is used to measure the small clearances with an accuracy of 0025 microns The effects of molecular rarefaction are studied by operating the slider bearing in different gas media of different mean free paths Bearings operating at extremely high local Knudsen numbers are studied without approaching excessively high bearing numbers Experimentally measured trailing edge clearances and pitch angles are compared with theoretical predictions using the modified Reynolds equation with velocity slip boundary conditions Excellent agreement between experiment and theory is found for clearances as high as 160 microns to as low as 0075 microns with corresponding ambient Knudsen numbers of 004 and 251, respectively

Corotating pressure waves without fast streams in the solar wind

Abstract: Voyager 1 and 2 magnetic field and plasma data are presented which demonstrate the existence of large scale, corotating, non-linear pressure waves between 2 AU and 4 AU that are not accompanied by fast streams. The pressure waves are presumed to be generated by corotating streams near the sun. For two of the three pressure waves that are discussed, the absence of a stream is probably a real, physical effect, viz., a consequence of deceleration of the stream by the associated compression wave. For the third pressure wave, the apparent absence of a stream may be a geometrical effect; it is likely that the stream was at latitudes just above those of the spacecraft, while the associated shocks and compression wave extended over a broader range of latitudes so that they could be observed by the spacecraft. It is suggested that the development of large-scale non-linear pressure waves at the expense of the kinetic energy of streams produces a qualitative change in the solar wind in the outer heliosphere. Within a few AU the quasi-stationary solar wind structure is determined by corotating streams whose structure is determined by the boundary conditions near the sun. Previously announced in STAR as N83-19694

THE VELOCITY OF SOUND BEHIND STRONG SHOCK WAVES IN 2024 Al

Abstract: Rarefaction waves were produced by impacting a target with a thin plate. An optical technique was used to determine where the rarefaction from the back surface of the impactor overtook the shock wave induced in a step wedge target. Bromoform was placed on the front surface. When the shock reached the liquid it radiated steadily until the rarefaction from the impactor overtakes it. The times when this occurred were used to determine where the rarefaction just overtook the shock in the target, and thus the sound velocity. The leading edge of this rarefaction wave travels at longitudinal sound velocity in solids. This velocity increases smoothly with pressure until shock heating causes the material to melt. The data indicate that melting on the Hugoniot of 2024 Al begins at about 125 GPa and is completed at 150 GPa.

Interaction of rarefaction waves with area reductions in ducts

Abstract: The interaction of a rarefaction wave with a gradual monotonic area reduction of finite length in a duct, which produces transmitted and reflected rarefaction waves and other possible rarefaction and shock waves, was studied both analytically and numerically. A quasi-steady flow analysis which is analytical for an inviscid flow of a perfect gas was used first to determine the domains of and boundaries between four different wave patterns that occur at late times, after all local transient disturbances from the interaction process have subsided. These boundaries and the final constant strengths of the transmitted, reflected and other waves are shown as a function of both the incident rarefaction-wave strength and area-reduction ratio, for the case of diatomic gases and air with a specific-heat ratio of 7/5. The random-choice method was then used to solve numerically the conservation equations governing the one-dimensional non-stationary gas flow for many different combinations of rarefaction-wave strengths and area-reduction ratios. These numerical results show clearly how the transmitted, reflected and other waves develop and evolve with time, until they eventually attain constant strengths, in agreement with quasi-steady flow predictions for the asymptotic wave patterns. Note that in all of this work the gas in the area reduction is initially at rest.

Rarefied gas flow in a cylindrical annulus

Abstract: The Hansen–Morse model of the linearized Wang Chang–Uhlenbeck equation is used to study the thermal transpiration and mechanocaloric effects for rarefied polyatomic gases in a cylindrical annulus, where boundary conditions are characterized by diffuse reflection. Phenomenological coefficients at all degrees of rarefaction are reported for physical parameters that represent helium, hydrogen, carbon dioxide, and air. Comparisons with isothermal flow data are given.

Detonation propulsion experiments and theory

Abstract: Test data are presented for the use of a single detonation of explosives in long-cone, short-cone, straight, and firing-plug nozzles to provide propulsion in a simulated Jupiter atmosphere, as well as the ambient gases N, CO2 and He. The long-cone nozzle yielded a progressive increase with ambient pressure for the higher molecular weight gases CO2 and N, while the lower molecular weight He and simulated Jupiter atmosphere showed a specific pulse decrease with increasing ambient pressure. The short-plug nozzle yielded a small specific impulse reduction with increasing ambient pressure, and its results were found to be nearly independent of ambient gas molecular weight. All data gathered are analyzed by using first principles, approximate blast wave theory predictions, and two-dimensional numerical calculations. Rarefaction and oscillatory wave phenomena are found to significantly influence specific impulse.

Interaction of oblique shock and detonatin waves

Abstract: : The interaction of an oblique shock wave and an oblique detonation wave which deflect the flow in the same direction is analyzed. The detonation wave is assumed to be an exothermic gasdynamic discontinuity. A criterion is developed and used to determine whether or not a theoretical solution of the problem describes a physically realizable interaction configuration. It is found that the reflected wave is, in general, a rarefaction wave. Only for very low values of the heat release parameter of the detonation wave the reflected wave has been found to be a shock wave. Domains of existence of such resulting wave interaction configurations are established for different values of the oncoming Mach number, 6 less than or equal M less than or equal 8, the heat release parameter, 3 less than or equal Q less than or equal 8, and the specific heat ratios for the combustion products behind the detonation wave, 1.30 less than or equal gamma less than or equal 1.33. It is also found that double discontinuity configurations, representing the refraction of a detonation wave at a combustible/non-combustible interface (a limiting case of the considered interaction problem) can exist for certain values of the flow parameters involved and for different specific heat ratios of the gases in front of and behind the detonation wave. The magnitudes of the heat release parameter and specific heat ratio of the combustion products affect significantly the interaction pattern of shock and detonation waves. It is, concluded that the interaction problem considered be based on a detailed thermochemical analysis for given combustible mixtures of gases. (Author)

Experimental and Computational Modeling of Rarefaction Wave Eliminators Suitable for the BRL 2.44 m Shock Tube

Abstract: : Three general types of rarefaction wave eliminators, RWEs (solid plate, vented plate, and lattice) were tested on a 1/48th scale model of the BRL 2.44 m shock tube. Pressures were monitored along the test section with piezoelectric transducers to determine effectiveness of the RWEs tested. All types were found to be equally effective in reducing the rarefactions but the lattice type was most difficult to use. The solid plate and vented plate RWEs would both be suitable for the 2.44 m shock tube. Predictions are produced using the NASA-Ames one-dimensional computer hydrocode. The hydrocode can be used effectively to model a RWE for the 2.44 m shock tube. Experimental and computational results are compared.

Interference of oblique shock waves of one family in a hypersonic flow

Abstract: A study is made of the irregular regime of interaction of two shock waves of the same direction when a hypersonic gas stream flows past bodies of complicated shape. It is shown that the rarefaction waves formed in the flow field significantly weaken the shock wave that approaches the body. This effect is confirmed by the results of an experiment and numerical calculations.

Seismic exploration system using pressure and velocity detectors

Abstract: f-1085(9729)-L : A seismic detection system includes pressure and velocity detectors producing outputs which are combined to substantially cancel ghost reflections. the pressure detector produces a positive output in response to upwardly travelling compressional waves and a negative output in response to downwardly travelling rarefaction waves. The velocity detector produces a positive output in response to upwardly travelling compressional waves and a positive output in response to downwardly travelling rarefaction waves. These outputs are filtered so that the impulse response of the rarefaction wave cancels. The filtered outputs are combined to produce an output in which the ghost reflection is substantially suppressed.

Collapse of metal tubes under explosive loading at a finite thickness of the explosive charge

Abstract: This article considers the case of relatively small thicknesses of explosive in order to show the important influence that the rarefaction wave has on the initial stage of collapse of the tube. Emphasis is placed on the simplicity of the model, which is important for engineering calculation purposes. An analysis of experimental and theoretical results relating to the initial phase of reduction of metal tubes shows that, starting from a time approximately corresponding to the arrival of the rarefaction wave, over a considerable interval the inclination of the outside surface of the tube wall is almost linear. The explosives examined are ammonite, RDX, and 50/50 TNT/RDX. In the model problem of a cylindrical piston, the motion is affected by the residual pressure in the gas, and the velocity of the outside boundary of the piston is almost constant. It is concluded that the proposed calculation scheme can be used to describe the initial phase of the explosive reduction of tubes even at relatively small charge thicknesses.

Ekman Layer on a Porous Plate in Slip Flow Regime

Abstract: The rotating flow of a viscous liquid on a porous plate with velocity slip at the wall is studied. Expressions for the velocity field and the skin friction have been obtained analytically. The effects of rotation and the rarefaction parameters on the flow and on the skin friction are discussed.

Simulation of a Nuclear Blast Wave with a Gaseous Detonation Tube

Abstract: : There is an ongoing interest in simulating nonideal blast environments for nuclear effects research. In particular, one would like to be able to impose peaked blast waves on real ground surfaces and experimentally measure the ensuing dusty airblast environment. Proposed here is a gaseous detonation tube blast simulator. A disposable (or reusable) shock tube would be constructed on a in-situ ground surface of interest. The tube would be sealed and filled with a detonatable gas mixture. When a planar detonation wave is initiated at one end of the tube, it induces a peaked blast wave which expands self-similarly with time--the longer the detonation run distance, the longer the blast wave duration. Similarity analysis of such a wave (which consists of a constant-velocity Chapman-Jouguet detonation followed by an adiabatic rarefaction wave expressed in terms of a Riemann characteristic) results in a closed-form analytic solution for the flow field time history. It is shown that the static and dynamic pressure waveforms associated with this detonation give a high fidelity simulation of a nuclear surface burst.

On the Determination of the Gas Temperature From the Velocity of the Muzzle Rarefaction Wave

Abstract: : The temperature of the propellant gas as it flows out of the muzzle of a gun is a principal factor in respect to the strength of the air blast which accompanies the discharge of the projectile. The temperature also plays a dominant role in respect to the occurrence of secondary combustion of flash. We discuss the fundamental basis for a method of determining the temperature from measurements of the velocity of the unloading wave or rarefaction created by the discharge of the projectile. The method is, of course, restricted to cases in which the projectile velocity is less than the speed of sound in the gas directly behind it. For charges which are completely burnt and in which the products of combustion at the muzzle are purely gaseous, three sources of error are identified. First, the measurement time may be approximately equal to the relaxation time for changes in chemical composition. This will result in dispersion and since the unloading wave contains components of all frequencies, part of the wave will move with the frozen wave speed and part move with the equilibrium speed. Due to dissipation the faster frozen components will be less detectable at increasing distances from the muzzle. Second, the unloading wave is not one-dimensional and the radial relaxation time is of the same order as the measurement time. Significant geometrical dispersion will result and will be superimposed on the chemical relaxation. Third, the temperature of the gas in the measurement zone may differ significantly from the space-mean value as a consequence of a non-uniform release of chemical energy by the propellant and the deviation may be to higher or to lower values.

Kinematic Waves in Vertical Sand Columns

Abstract: Waves of bulk density change in vertical columns of sand are modeled as kinematic waves. A flow-concentration curve for sand movement in a vertical column is developed and shown to be similar to flow concentration curves for traffic flow on long crowded roads. As an application of kinematic wave theory, the speed of a strong rarefaction wave in a sand column is obtained.