摘要:

The prediction of Roppo, Davis, and Rosenblat [Phys. Fluids27, 796 (1984)] that hexagons should appear near threshold in a Rayleigh–Be´nard cell under external modulation of the temperature is reconsidered with a view to determining the experimental observability of the effect. It is found that in the limit of low‐modulation amplitude &dgr; considered by Roppoetal. the effects are qualitatively as given by these authors, but considerably smaller quantitatively. The validity limits of the small‐&dgr; expansion are clarified and results of an alternative theory of hexagonal effects, valid at arbitrary amplitude &dgr; and frequency &ohgr;, are briefly summarized. Hexagons will only be observable if large amplitudes can be achieved.

ISSN:0031-9171    

DOI:10.1063/1.866359

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

It is proved that the two‐dimensional Taylor vortex array, which is an exact unsteady solution of the Navier–Stokes equation, is globally and asymptotically stable in the mean with respect to three‐dimensional periodic disturbances. A time‐dependent bound on the decay rate of the kinetic energy of disturbances is obtained.

ISSN:0031-9171    

DOI:10.1063/1.866522

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

The Reynolds number for transition from singly to doubly periodic Taylor–Couette flow is studied experimentally and found to vary inversely with the aspect ratio &Ggr; of the fluid column. This transition Reynolds number is also dependent on the numbermof azimuthal waves. For a givenm, the type of modulating state, which results after this transition, is not affected by &Ggr;, nor does the transition Reynolds number differ for the different types of modulating states which can occur.

ISSN:0031-9171    

DOI:10.1063/1.866360

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

In systems of ordinary differential equations representing the truncation to any order of the spectral, barotropic vorticity equation for two‐dimensional flows in rotating fluids, subject to constant forcing and dissipation, large values of absolute rotation inhibit the occurrence of equilibrium states other than the basic, forced regime, and promote transitions to periodic oscillations, via Hopf bifurcation.

ISSN:0031-9171    

DOI:10.1063/1.866361

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

The stability of a jet in a compressible fluid is examined for the case of a rectangular velocity profile, where the jet is a cylindrical region of uniform velocity separated from the external uniform medium by a vortex sheet. Numerical results are presented for the maximum instability of the ordinary mode that arises when the flow is supersonic. These instabilities have ane‐folding length and a typical wavelength greater than the jet radius.

ISSN:0031-9171    

DOI:10.1063/1.866362

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Results of precise measurements on the variation of drift cyclotron loss cone frequency and perpendicular wavenumber as a function of ion density are reported. Careful quantitative comparisons to theory are made. In particular, it was found that a local linear slab model accurately predicted the unstable mode frequencies, even under conditions where nonlocal effects should be significant—i.e., when characteristic gradient scale lengths are on the order of an unstable mode’s wavelength. Inaccurate predictions of unstable perpendicular wavelength, however, may be a consequence of nonlocal effects.

ISSN:0031-9171    

DOI:10.1063/1.866363

出版商:AIP    

年代:1987

数据来源: AIP

ISSN:0031-9171    

DOI:10.1063/1.866532

出版商:AIP    

年代:1987

数据来源: AIP