摘要:

In Part I of this paper with the same title [Stewartson (1978)] the evolution of a Rossby wave of amplitudeO(ε) forced on a uniform shear was studied. Timestwere considered such thatt=O(1) and ε½t= O(1) and it was shown that as ε½t→ ∞ the vorticity in the neighbourhood of the critical layer does not tend to a limit though the velocity jump across it tends to zero. The discussion concentrated on inviscid flow so that λ= R−1ε−3/2was zero. In the present paper the unsteady investigation is extended to values of λ ≪ 1, and it is shown that the vorticity in the critical layer diffuses outwards until it has an effect on the imposed shear which is larger by a factor ε−½than that due of the wave disturbance. This is corroborated by a closer examination of the Benney-Bergeron theory for λ ≪ 1 in which the correctness of the conjecture of Haberman that the vorticity must be continuous across the critical layer is demonstrated. Thus in this limit also there is anO(ε½) modification to the imposed shear.

ISSN:0309-1929    

DOI:10.1080/03091927808242627

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

In the case of equal layer depths and uniform vertical energy density, the quadratic integral invariants of two-layer rotating flow are close analogs of the corresponding invariants of two-dimensional turbulence. A simple theory based on the invariants and on the selection rules governing triad interactions qualitatively explains the major features of forced equilibrium flow. The general physical picture is very similar to that of Rhines (1977). In the geophysically interesting case. net baroclinic energy is produced at low wavenumbers and moves toward hisher wavenumbers in relatively nonlocal triad interactions which are unhampered by the constraint to conserve enstrophy. The energy converts to barotropic mode and moves back toward low wavenumbers in more local interactions which are similar to those in two-dimensional turbulence. Equilibrium wavenumber spectra are obtainable from a simple Markovian turbulence closure model in which the estimate of turbulent scramhling rate includes a contribution from vortex stretching along the axis of rotation. Numerical experiments with the closure model confirm the qualitative predictions and demonstrate the sensitivity of the flow at low wavenumbers to changes in the forcing and dissipation.

ISSN:0309-1929    

DOI:10.1080/03091927808242628

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

We describe a sequence of two-dimensional numerical simulations of inflection point instability in a stably stratified shear flow near the ground. The fastest growing Kelvin-Helmholtz modes are studied in detail; in particular we investigate the growth inhibiting effect of the ground which is predicted by linear theory and the Reynolds number dependence of the process of growth to finite amplitude. We consider flows which are both above and below the critical Reynolds number (Re = 300) which has been reported by Woods (1969) to mark the boundary between flows which have turbulent final states and those which do not. A global energy budget reveals a fundamental difference in character of the finite amplitude billows in these two Reynolds number regimes. However, for relatively high Reynolds numbers (Re = 103) we do not find any explicit evidence for secondary instability. Above the transition Reynolds number the modified mean flow induced by wave growth is characterized by a splitting of the original shear layer and of the in version in which it is embedded.

ISSN:0309-1929    

DOI:10.1080/03091927808242629

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

It is investigated whether large-scale motions which are driven by a magnetic field itself generated by the α2-dynamo-mechanism are able to react on the field in such a manner that the ohmic dissipation is increased nonlinearly and the growth of the field is limited. The problem is attacked in two different ways:

ISSN:0309-1929    

DOI:10.1080/03091927808242630

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

A new method is introduced to produce a uniform stratified flow over a stationary obstacle in an open channel. The flow is achieved by discharging the flow from the channel through a sink. The details of the sink are unimportant. The flow speed is limited only by the sink capacity. Selective withdrawal at lower densimetric Froude numbers is effectively eliminated through the use of a contraction. The standing, free-surface, long wave arising from the initiation of the flow is also eliminated by the contraction. Experiments are conducted for flow over a sphere for a range of Reynolds numbers from O(102) to O(103) and a range of Richardson numbers from O(10−1) to O(10). Dye and neutrally buoyant droplets are used for quantitative analysis of the wake structure. The wake is also probed by a hot-film anemometer. The frequency of vortex shedding is obtained. Comparison with data from towed experiments is also presented.

ISSN:0309-1929    

DOI:10.1080/03091927808242631

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

By D. J. Tritton. Van Nostrand Reinhold Company xv + 362 pp. $27.50 (ISBN 0 442 301 31 6 cloth). $11.95 (ISBN 0 442 301 32 5 paper) 1977.

ISSN:0309-1929    

DOI:10.1080/03091927808242632

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

ISSN:0309-1929    

DOI:10.1080/03091927808242633

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The transition between axisymmetric and non-axisymmetric régimes of flow in a rotating annulus of liquid subject to horizontal temperature gradient is known from previous experimental studies to depend largely on two dimensionless parameters. These are Θ, which is proportional to the impressed density contrast Δρ and inversely proportional to the square of the angular speed of rotation ω, and 𝒯 (Taylor number), which is proportional to ω2/v2where v is the coefficient of kinematic viscosity. At moderate values of 𝒯, around 107, the critical value of Θ above which axisymmetric flow is found to OCCUT and below which non-axisymmetric fully-developed baroclinic waves (sloping convection) occur, is fairly insensitive to 𝒯. Though sharp, the transition exhibits marked hysteresis when the upper surface of the liquid is free (but not when the upper surface is in contact with a rigid lid), and it is argued on the basis of the experimental evidence supported by various results of baroclinic instability theory that both the sharpness of the transition and the hysteresis phenomenon are consequences of the combined effects of potential vorticity gradients and viscosity on the process of sloping convection.

ISSN:0309-1929    

DOI:10.1080/03091927808242634

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The transition from the flow in the wave regime of the rotating annulus to the flow in the upper symmetric regime has been investigated experimentally in two apparatus with positive as well as negative radial temperature gradients. It has been found that the absolute value of the radial temperature difference at which the transition occurs depends on the sign of the temperature gradient. The velocities of the wave patterns relative to the rotating annulus have also been measured, with positive and negative temperature gradients and four different rotation rates, with the fluid being in contact with a rigid lid. Repeated changes in the direction in which the patterns move have been observed, at different values of the negative radial temperature gradient. Abrupt increases of the pattern velocities occurred with the transition from 2 waves to 1 wave, when the temperature gradient was either positive or negative.

ISSN:0309-1929    

DOI:10.1080/03091927808242635

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

A model is developed for small scale thermally driven turbulent convection in rapidly rotating systems. The Boussinesq equations of adiabatic and inviscid flow are perturbed about a basic state which is superadiabatic and which contains a horizontal temperature gradient balanced by a geostrophic wind. The growth rates and length scales of the most unstable modes are determined. It is found that these modes are either zonally or latitudinally symmetric, depending on the latitude and the horizontal temperature gradient. The transports of heat and momentum by the modes are computed. The linear amplitudes are assumed to be limited by shear instability. The model predicts a latitude dependent eddy diffusivity. The applicability of the model to astrophysical and planetary bodies is briefly discussed.

ISSN:0309-1929    

DOI:10.1080/03091927808242636

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor