摘要:

The onset of thermal convection in a horizontal fluid layer heated from below and bounded, above and below, by zero shear boundaries is studied experimentally. The measured value of the critical Rayleigh number is in reasonable agreement with the closed form solution obtained by Rayleigh and is in good agreement with that expected for the actual thermal boundary conditions experienced in the laboratory.

ISSN:0031-9171    

DOI:10.1063/1.1692642

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The hydrodynamic stability of viscous flow between eccentric rotating cylinders has been studied experimentally. The ratio of the radii of the cylinders was 1 :2; several eccentricities were investigated. In the concentric configuration good agreement was achieved with previous experimental and theoretical work. Results obtained with the cylinders rotating in the same direction show that the effect of eccentricity can be stabilizing or destabilizing depending upon the speed of the outer cylinder and the amount of eccentricity. In the counterrotating case, a new flow phenomenon different from the usual vortex pattern was observed for large eccentricity.

ISSN:0031-9171    

DOI:10.1063/1.1692643

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Experimental determination of the frequencies of the fundamental axisymmetric gravity mode in a nonrotaing flat‐bottom circular cylinder has been made for a series of forcing disk sizes with the aim of extrapolation to infinitesimal disk size. Two different resonance criteria, either maximum amplitude of the mode at the rim of the basin or minimum phase‐lag between the water and the forcing disk at the center have been used. The periods determined in this manner showed systematic differences. A comparison of these experimental values with the theoretical values for an equivalent annulus showed that the water below the disk behaves more or less as an isolated material region.

ISSN:0031-9171    

DOI:10.1063/1.1692644

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Cagniard's method is used to find the transient solution for the reflection of line‐source generated waves from an interface between two fluid half‐spaces in relative motion, but with the same density and sound speed. The resulting solution for the reflected wave in the (normally motionless) lower half‐space may be conveniently considered as the sum of a specularly reflected wave, a refracted arrival wave, a neutral stability wave comprising one or more resonance waves, and an instability wave. Critical angles limiting the appropriate domains of reception are derived for each wave type as a function of the Mach numberMof the fluid motion in the upper half‐space. The instability wave appears in the solution whenM < 2 2. This feature may possibly represent the prediction of the spatial extent of a turbulent region arising from an inherent instability of the ambient medium which has been triggered by the arival of the incident pulse at the interface.

ISSN:0031-9171    

DOI:10.1063/1.1692645

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A stability criterion is found for an initially static, stratified fluid subject to an electric stress. The equilibrium fluid density, permittivity, viscosity, and space charge distributions are functions of the vertical spatial coordinate, with gradients directed parallel to the imposed electric field intensity and gravitational acceleration. In the limit where the fluid is perfectly insulating, sufficient conditions for stability are found; the principle of exchange of stabilities is shown, and variational principles derived for the eigenfrequencies and, in the case of no space charge, for the critical field strength. An experiment demonstrates instability in the dielectrophoretic limit of no bulk free charge. The property gradients are induced thermally, and incipience of instability, as measured by the Schmidt‐Milverton heat‐transfer technique, is successfully predicted by the theoretical criterion.

ISSN:0031-9171    

DOI:10.1063/1.1692646

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Steady, one‐dimensional, oblique, hydromagnetic waves of small but finite amplitudes in a cold plasma are considered. Analysis is based on an equation derived by Saffman and is restricted to a class of the waves with a large critical Mach number and high‐frequency oscillations. Solutions are given in an asymptotic expansion. In the lowest order of perturbation the equation is integrated to give the solutions in closed form, which exhibit compressional solitary waves.

ISSN:0031-9171    

DOI:10.1063/1.1692647

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The equations of inviscid magnetohydrodynamics, appropriate when the induced magnetic field can be neglected, are studied when the interaction parameterNis very large. The limit equations, in which the nonlinear inertia terms do not appear, cannot fully describe general inviscid flow situations suggesting the existence of inviscid boundary layers in which the missing terms must be reinstated. Similarity solutions are obtained for two kinds of layers, one perpendicular to the magnetic field and the other parallel to the magnetic field. The parallel layers are backward jets and constitute our most important result. The existence of the perpendicular layers, which look like reversed shock layers, may have implications for flow in ducts with discontinuous area changes.

ISSN:0031-9171    

DOI:10.1063/1.1692648

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A long, tenuous, but well‐collimated beam of luminosity is observed to emerge from the plume of a magnetoplasmadynamic arc operated in a fiberglass vacuum tank. Examination of the beam trajectory in the magnetic field of the earth, and in other externally imposed fields indicates that the beam consists of a stream of 100‐V electrons emitted from the core of the arc, which excite background gas particles to luminosity along their path to the tank wall. Although this beam carries a negligible portion of the arc current, the particle energy corresponds to some two‐thirds of the arc voltage, and the beam is capable of damaging material surfaces which it encounters. Formation and emission of such a well‐collimated stream of electrons of this energy seems incompatible with present concepts of magnetoplasmadynamic arc structure, and may have implications for space thruster applications.

ISSN:0031-9171    

DOI:10.1063/1.1692649

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The effect of radiation upon the state of the gas behind a strong shock wave is studied. The equations of radiation gas dynamics are used, and it is shown that the two characteristic times,&tgr;the time for radiative cooling, and&lgr;/c, the mean time of photon flight, determine whether a strong shock wave is optically thin. The steady‐state shock jump conditions for hydrogen are determined for plasmas which are optically thin, and they are compared with the Saha equilibrium solutions. The temperature decay, plasma velocity, and density behind strong shock waves are determined for the case of an optically thin bremsstrahlung radiating plasma. The time‐dependent equations of the motion of a fluid interacting with radiation are examined and the radiative terms in these equations are presented as part of a general solution of the time‐dependent radiative transfer equation.

ISSN:0031-9171    

DOI:10.1063/1.1692650

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Experimental investigations of precursors ahead of pressure‐driven shock waves in argon lead to the conclusion that for the existing conditions electron diffusion is the dominant cause of the precursors. A theoretical analysis of the electron temperature and density is presented.

ISSN:0031-9171    

DOI:10.1063/1.1692651

出版商:AIP    

年代:1969

数据来源: AIP