摘要:

The extension of the Way‐Libby probe to permit the measurement of two velocity componentsuand&ugr;in the usual notation, and the mass fractioncof helium in turbulent flows involving helium‐air mixtures is described. The accuracy of the technique, especially the sensitivity to flow deflection, is carefully assessed. Interesting results obtained in applying the new probe show,inter alia, highly skewed probability density functions of helium concentration in an internal flow.

ISSN:0031-9171    

DOI:10.1063/1.1694895

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Following Deissler's approach the concentration fluctuation of a dilute contaminant undergoing a first‐order chemical reaction is studied. Two‐, three‐, and four‐point correlation equations have been obtained and to make the set of equations determinate, the terms containing quintuple correlations are neglected in comparison to those containing lower‐order correlation terms. The solution obtained gives the state of concentration fluctuation in a homogeneous turbulence between its initial and final periods.

ISSN:0031-9171    

DOI:10.1063/1.1694896

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Two‐dimensional convection in a layer of volumetrically heated fluid confined between free horizontal boundaries has been studied using numerical experiments. The dependence on the appropriate modified Rayleigh number of the maximum horizontally averaged temperature and of the fraction of thermal flux emerging from the upper surface has been found forRaH ≤ 80 RaHC.

ISSN:0031-9171    

DOI:10.1063/1.1694897

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

An asymptotic analysis is made of the unsteady boundary layer flow generated impulsively in an incompressible homogeneous viscous fluid bounded by an infinite porous plate with uniform suction or blowing to describe the manner of the transient approach to the ultimate steady state. It is shown that the initial motion for small times describes the general features of the unsteady boundary‐layer flow and consists of three boundary layers on the plate which are unaffected by rotation. In subsequent large times, the effect of rotation manifests itself through inertial oscillations of frequency2&OHgr;and the generation of diffused waves propagating outward from the plate with velocity2(&OHgr;&ngr;)1/2a1. It is found that the final steady boundary layers are established in a dimensional time(4/&OHgr;) (S4/4E2 + 4)−1/2which decreases with an increase in the suction parameter. Several limiting cases of interest are recovered from this analysis.

ISSN:0031-9171    

DOI:10.1063/1.1694898

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

With a method previously applied to thermal transpiration and planar radiometric force, the force on a spherical aerosol particle in a gas which sustains a temperature gradient is analyzed. Expressions for thermal force and thermal velocity span all values of the particle Knudsen number and show the effect of imperfect accommodation. The results are compared with other theories and with experimental data.

ISSN:0031-9171    

DOI:10.1063/1.1694899

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Results of exact, full three‐dimensional solutions of the incompressible laminar boundary layer over a prolate spheroid at an extremely high incidence are presented. This extremely high incidence problem is characterized by features reflecting the predominance of the circumferential flow over the meridional flow and, more importantly, by a change of separation pattern from an open type to a closed type. These features include much larger circumferential skin friction than meridional skin friction and that the limiting streamlines are more closely oriented along the parallels.

ISSN:0031-9171    

DOI:10.1063/1.1694900

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A computer study is made of the change in adiabatic invariant for a plane pendulum when a slow variation in the pendulum length forces the pendulum to change from circularly rotating motion to an oscillating state. The numerical results are shown to be in good agreement with a simply derived analytic expression which itself is generalizable to calculations of nonadiabatic transitions in other problems.

ISSN:0031-9171    

DOI:10.1063/1.1694901

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Isolated, one‐dimensional channels of electromagnetic radiation in a plasma are shown to be unstable to bending perturbations. Letlbe the wave vector of the perturbation along the channel,kbe that of the radiation, andC8be the sound speed. Then, the growth rate&ggr; ∼ lC8forl/k ≪ 1.

ISSN:0031-9171    

DOI:10.1063/1.1694902

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The influence of ion tail formation on the dynamical behavior and anomalous resistivity of a current‐carrying plasma is studied within the context of a quasilinear model that includes ion resonance broadening as a possible quasi‐saturation mechanism for the ion acoustic instability. Although the detailed time development of macroscopic plasma parameters depends onnh/ni(the ratio of ion tail density to total ion density), the value of anomalous resistivity at quasi‐saturation is found to be relatively insensitive to the formation of a low‐density high‐energy ion tail. For example, ifnh/ni = 0.2, the anomalous resistivity is lowered by 15% relative to its value in the absence of an ion tail.

ISSN:0031-9171    

DOI:10.1063/1.1694903

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Heating of a collisionless plasma by utilizing the spatial resonance of shear Alfve´n waves is proposed and application to toroidal plasmas is discussed. The resonance exists due to the nonuniform Alfve´n speed. This heating scheme is analyzed in one dimension including the effects of a shear magnetic field and plasma compressibility. For plasmas with smooth nonuniformities (| k⊥l | ≫ 1, k⊥is the wavenumber prependicular to the ambient magnetic field and the nonuniformity direction, andlis the scale length of the nonuniformity), the energy absorbed per unit surface area per driving cycle is[b02(&mgr;0k⊥)−1]. Here,b0is the flux density of the driving magnetic field evaluated at the resonant point. With sharp nonuniformities(| k⊥l | ≪ 1), absorption is large if the surface eigenmode is excited. The corresponding value is[b02(&mgr;0k⊥)−1(k⊥l)−1]. Otherwise, it is[b02(&mgr;0k⊥)−1(k⊥l)].

ISSN:0031-9171    

DOI:10.1063/1.1694904

出版商:AIP    

年代:1974

数据来源: AIP