摘要:

A class of eccentric cylinder solutions negates the Moore–Rott–Sears conjecture at steady instream dividing streamlines.

ISSN:0031-9171    

DOI:10.1063/1.864322

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Experimental measurements of the longitudinal dispersion coefficient in oscillatory pipe flow of binary gas mixtures at high oscillation frequencies are presented. The magnitude of the dispersion coefficient is shown to be directly proportional to the product of the square of the oscillation amplitude and the first power of frequency.

ISSN:0031-9171    

DOI:10.1063/1.864323

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

For typical tokamak parameters, it is shown that superthermal magnetostatic convective‐cell fluctuations can be nonlinearly excited by a moderate level of kinetic drift‐Alfve´n turbulence (e.g., &dgr;n/n0∼1%). Effects on the plasma cross‐field transport and the nonlinear evolution of drift‐Alfve´n turbulence are also briefly discussed.

ISSN:0031-9171    

DOI:10.1063/1.864324

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Ambipolar flow in a turbulent plasma is investigated by combining a WKB treatment of the waves with a turbulent collision operator resulting from either quasilinear theory or certain renormalized turbulence theories. If the wave momentum has a flow from outgoing waves, then particle diffusion is not intrinsically ambipolar, and the time variation of the electric potential profile is determined by the turbulent spectrum. However, in most cases of practical interest, as in the drift‐wave problem, this effect is small; and in steady state, equal rates of stochastic diffusion are predicted for electrons and ions.

ISSN:0031-9171    

DOI:10.1063/1.864325

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Convective cells are excited externally in a fully ionized magnetized plasma, and their space‐time evolution is investigated by two‐dimensional potential measurements. A positive cell is excited externally in the ‘‘scrape‐off’’ layer of a plasma column produced by surface ionization. Its interaction with the main plasma produces a new cell with negative polarity. The two cells propagate close to each other and interact only through a mutual perturbation of orbits.

ISSN:0031-9171    

DOI:10.1063/1.864326

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A Monte Carlo calculation of resonant diffusion coefficients in the ELMO bumpy torus (EBT) is described and is shown to agree well with analytic theory in a regime where the assumptions of local, diffusive behavior are valid. Since present and future EBT devices do not fall into this regime, local diffusion theory may not be entirely applicable.

ISSN:0031-9171    

DOI:10.1063/1.864327

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Five previously unobserved and unpredicted flows are found to occur in a fluid contained between concentric cylinders with the inner cylinder rotating faster than, but in the same direction as, the outer cylinder. Flow visualization and spectral studies of these flows yield the following descriptions: (1) Twisted Taylor vortices—each Taylor vortex contains from 14 to 30 apparent twists. (2) Wavy inflow boundaries—traveling azimuthal waves appear on the inflow boundary between Tayor vortices. (3) Wavy outflow boundaries—traveling azimuthal waves appear on the outflow boundary between Taylor vortices. (4) Wavelets—small‐amplitude traveling azimuthal waves of high wavenumber appear on both inflow and outflow boundaries of the vortices; this flow is distinct from the wavy vortex flows observed with only the inner cylinder rotating. (5) Braided vortices—the vortices appear to wrap around one another in an irregular fashion. The first four flow patterns, produced through quasistatic changes in the inner‐cylinder speed with the outer‐cylinder speed fixed, can be periodic in the azimuthal and axial directions; in contrast, the braided‐vortex pattern, produced through a rapid increase of the inner‐cylinder speed with the outer‐cylinder speed fixed, has neither axial nor azimuthal periodicity. The power spectra of all five flows contain sharp components. The ranges of cylinder speeds for the occurrence of these flows, and for some cases, the wave speeds and wavenumbers are determined.

ISSN:0031-9171    

DOI:10.1063/1.864328

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Bicoherency spectrum measurements are used to study the nonlinear dynamics of spectral broadening during natural transition of a two‐dimensional wake. Dominant nonlinear interactions are identified. The results are compared with multiple instability controlled transition experiments.

ISSN:0031-9171    

DOI:10.1063/1.864309

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The normal‐fluid and superfluid vorticity, produced by forcing He II out of a tube 0.8 cm in inner diameter at velocities of about 10 cm/sec, is investigated in the region in front of the tube orifice. The method of circulation measurement uses the flow‐induced variations of the traveling times of second‐sound shock waves. The evolution of large‐scale vortex rings with a nearly homogeneous vorticity distribution is observed and measured. Their translational velocity and circulation are measured at temperatures 1.28 K≤T≤2.02 K in the region 1–7 orifice diameters downstream from the orifice. Strong evidence for a marked dependence of the normal‐fluid circulation in the vortex ring on temperature and time is found. It points out the importance of the mutual friction force for both macroscopic velocity fields.

ISSN:0031-9171    

DOI:10.1063/1.864310

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

An equation of the Korteweg–deVries (KdV) type is derived for the study of nonlinear surface waves under gravity with surface tension and edge constraints in a channel of variable cross section. The approach used here is based upon a nonlinear ray method. An example of a symmetric rectangular channel with variable width is given.

ISSN:0031-9171    

DOI:10.1063/1.864311

出版商:AIP    

年代:1983

数据来源: AIP