摘要:

It is suggested that, in an inhomogeneous turbulent flow, the flux of a passive scalar admixture should be modeled to first order by a linear combination of gradient transport and convective transport, where the convective transport coefficient is proportional to the gradient of the (gradient) ‐transport coefficient. A simple model is presented which allows determination of the coefficient of proportionality.

ISSN:0031-9171    

DOI:10.1063/1.861200

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

A new model is presented for estimating the breakup rate of drops dispersed in a continuous liquid phase under isotropic turbulent conditions.

ISSN:0031-9171    

DOI:10.1063/1.861201

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

It is shown that the observed effects of small amounts of streamline curvature on turbulence are accounted for by the curvature terms which appear in the Reynolds stress equations and in the turbulence model of Launder, Reece, and Rodi. Because of the smallness of these terms, this is a surprising result, but their effect is shown to appear in a magnified form in the effective eddy viscosity. A comparison is made between computed solutions of the modeled Reynolds stress, mean momentum and dissipation rate equations, and experimental data for curved wall jets, a curved free jet, and curved boundary layers. The curvature effects are well predicted when the curvature terms are included. The turbulence model implies that the turbulence shear stress is relatively insensitive to longitudinal accelaration which seems to be in reasonable agreement with experiment.

ISSN:0031-9171    

DOI:10.1063/1.861202

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

A plane inertial wave, traveling in an incompressible liquid of density &rgr;1, is incident upon the plane interface defining another incompressible liquid of density &rgr;2. The reflection and refraction of the wave are studied, and the mathematical results are as interesting as those for the reflection of a plane inertial wave striking a plane, rigid wall. In particular, not only the reflection, but also the refraction, can be ’’backward,’’ a backward refracted wave occurring whenever the reflected wave is forward, and vice versa. There is no possibility of total reflection.

ISSN:0031-9171    

DOI:10.1063/1.861203

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

The theory of self‐induced separation at moderate Mach numbers is extended to hypersonic flows under the Newtonian approximation. Numerical solutions of the relevant boundary‐layer equations are compared with experimental data.

ISSN:0031-9171    

DOI:10.1063/1.861210

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

The dispersion relations for Alfve´n waves with exp(jm&Vthgr;) azimuthal dependency are calculated for a cylindrical, cold, collisionless plasma. If the electron inertia term is included in the dielectric tensor, then, in a bounded plasma, there are two transverse wavenumbers for each axial wavenumber. The phase velocities form=0, ±1 fast and slow waves are calculated for different vacuum thicknesses between the uniform plasma and the metal walls. It is found thatm=0 and −1 fast waves each experience a cutoff below a given frequency, but them=+1 fast wave can propagate even at very low frequencies provided the vacuum layer is of sufficient thickness. The calculations are shown to agree with previously reported experimental results.

ISSN:0031-9171    

DOI:10.1063/1.861211

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

Expressions are derived for the spatial damping rate of ion acoustic waves traveling through inhomogeneous plasmas enclosed in plane, cylindrical, or spherical surfaces. The waves are assumed to have the same symmetry as the plasma. The solutions are valid for wavelengths small compared with the size of the plasma and negligible Landau damping. Ionization of the gas by beam or plasma electrons and ion‐neutral collisions are taken into account. The wave is more heavily damped when it travels from the plasma boundary to the center than vice versa.

ISSN:0031-9171    

DOI:10.1063/1.861212

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

The characteristics of dispersion and Landau damping of ion acoustic waves are experimentally investigated in an argon‐helium plasma with varying ion composition ratio. The dispersion relations change continuously from the argon mode to the helium mode. The damping rate has a maximum when the ion number density ratio (r=nHe/nA+nHe) is about 0.08. This maximum is attributed to the resonance of helium ions with the argon mode ion acoustic wave and is consistent with theoretical predictions.

ISSN:0031-9171    

DOI:10.1063/1.861213

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

The ion scattering rate due to the Post–Rosenbluth convective loss‐cone instability is calculated for general geometry. Noise generated by particle discreteness is amplified by the instability, the details of which are sensitively dependent upon the spatial variation of plasma parameters. Ray equations are developed for the transport and amplification of wave energy.

ISSN:0031-9171    

DOI:10.1063/1.861214

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

An interaction between a plasma and a neutral gas in relative motion is demonstrated. If the relative velocity is high enough, the interaction leads to heating of the electrons, partial ionization of the gas, and braking of the motion. The limiting velocity is found to be very close to Alfve´n’s critical velocity. Two new means of plasma diagnostics are tried for the first time in this experiment. Measurements of the polarization of emitted spectral lines have yielded information on the velocity distribution of the electrons. An ion beam interaction technique has been employed to determine the density of energetic electrons. New evidence is also presented of electron heating and of the necessity of a magnetic field for the interaction to take place. The previously observed minimum gas density is also discussed.

ISSN:0031-9171    

DOI:10.1063/1.861215

出版商:AIP    

年代:1975

数据来源: AIP