scholarly journals The Role of Density Stratification in Generating Zonal Flow Structures in a Rotating Fluid

2008 ◽  
Vol 673 (2) ◽  
pp. 1154-1159 ◽  
Author(s):  
Martha Evonuk
Keyword(s):  
Zonal Flow ◽  
Density Stratification ◽  
Flow Structures ◽  
Rotating Fluid

Experiments with baroclinic vortex pairs in a rotating fluid

1986 ◽  
Vol 173 ◽  
pp. 501-518 ◽  
Author(s):  
R. W. Griffiths ◽  
E. J. Hopfinger
Keyword(s):  
Velocity Field ◽  
Potential Energy ◽  
Baroclinic Instability ◽  
Point Vortices ◽  
Density Stratification ◽  
Rotating Fluid ◽  
Vortex Pairs ◽  
Layer Density

When vortices are generated in one layer of a rotating, two-layer density stratification, the velocity field of each vortex is strongly baroclinic within a distance of order one Rossby radius from its centre. In this system there are two classes of vortex pairs: those pairs (consisting of vortices of opposite signs) for which the vortices are in the same layer, and those for which the vortices are in opposite layers. We pay particular attention to a laboratory demonstration of the properties of the latter class. These vortex pairs have the ability to transport density (or heat) in the horizontal, and provide a means for describing the release of potential energy by baroclinic instability. We also observe that interactions of real vortices and real vortex pairs differ from those computed for point vortices.

scholarly journals The Role of the Divergent Circulation for Large-Scale Eddy Momentum Transport in the Tropics. Part I: Observations

2019 ◽  
Vol 76 (4) ◽  
pp. 1125-1144 ◽  
Author(s):  
Pablo Zurita-Gotor
Keyword(s):  
Momentum Flux ◽  
Large Scale ◽  
Zonal Flow ◽  
Stationary Wave ◽  
Hadley Cell ◽  
Momentum Transport ◽  
Mean Flow ◽  
Meridional Transport ◽  
The Tropics

Abstract This work investigates the role played by the divergent circulation for meridional eddy momentum transport in the tropical atmosphere. It is shown that the eddy momentum flux in the deep tropics arises primarily from correlations between the divergent eddy meridional velocity and the rotational eddy zonal velocity. Consistent with previous studies, this transport is dominated by the stationary wave component, associated with correlations between the zonal structure of the Hadley cell (zonal anomalies in the meridional overturning) and the climatological-mean Rossby gyres. This eddy momentum flux decomposition implies a different mechanism of eddy momentum convergence from the extratropics, associated with upper-level mass convergence (divergence) over sectors with anomalous westerlies (easterlies). By itself, this meridional transport would only increase (decrease) isentropic thickness over regions with anomalous westerly (easterly) zonal flow. The actual momentum mixing is due to vertical (cross isentropic) advection, pointing to the key role of diabatic processes for eddy–mean flow interaction in the tropics.

scholarly journals The role of magnetic fields for planetary formation

2008 ◽  
Vol 4 (S259) ◽  
pp. 249-258 ◽  
Author(s):  
Anders Johansen
Keyword(s):  
Magnetic Fields ◽  
Turbulent Diffusion ◽  
Planet Formation ◽  
High Pressures ◽  
Mixing Time ◽  
Zonal Flow ◽  
Coherence Time ◽  
Maxwell Stress ◽  
Turbulent Diffusion Coefficient

AbstractThe role of magnetic fields for the formation of planets is reviewed. Protoplanetary disc turbulence driven by the magnetorotational instability has a huge influence on the early stages of planet formation. Small dust grains are transported both vertically and radially in the disc by turbulent diffusion, counteracting sedimentation to the mid-plane and transporting crystalline material from the hot inner disc to the outer parts. The conclusion from recent efforts to measure the turbulent diffusion coefficient of magnetorotational turbulence is that turbulent diffusion of small particles is much stronger than naively thought. Larger particles – pebbles, rocks and boulders – get trapped in long-lived high pressure regions that arise spontaneously at large scales in the turbulent flow. These gas high pressures, in geostrophic balance with a sub-Keplerian/super-Keplerian zonal flow envelope, are excited by radial fluctuations in the Maxwell stress. The coherence time of the Maxwell stress is only a few orbits, where as the correlation time of the pressure bumps is comparable to the turbulent mixing time-scale, many tens or orbits on scales much greater than one scale height. The particle overdensities contract under the combined gravity of all the particles and condense into gravitationally bound clusters of rocks and boulders. These planetesimals have masses comparable to the dwarf planet Ceres. I conclude with thoughts on future priorities in the field of planet formation in turbulent discs.

The Influence of Wing Span and Angle of Attack on Racing Car Wing/Wheel Interaction Aerodynamics

2017 ◽  
Vol 139 (6) ◽  
Author(s):  
Sammy Diasinos ◽  
Tracie J. Barber ◽  
Graham Doig
Keyword(s):  
Angle Of Attack ◽  
Ground Effect ◽  
Navier Stokes ◽  
Flow Structures ◽  
Wing Span ◽  
Complex Interactions ◽  
Lift And Drag ◽  
Two Bodies ◽  
Wing In Ground Effect

A numerical-based (Reynolds-averaged Navier–Stokes (RANS)) investigation into the role of span and wing angle in determining the performance of an inverted wing in ground effect located forward of a wheel is described, using a generic simplified wheel and NACA 4412 geometry. The complex interactions between the wing and wheel flow structures are investigated to explain either increases or decreases for the downforce and drag produced by the wing and wheel when compared to the equivalent body in isolation. Geometries that allowed the strongest primary wing vortex to pass along the inner face of the wheel resulted in the most significant reductions in lift and drag for the wheel. As a result, the wing span and angle combination that would produce the most downforce, or least drag, in the presence of the wheel does not coincide with what would be assumed if the two bodies were considered only in isolation demonstrating the significance of optimizing these two bodies in unison.

Laboratory and numerical studies of baroclinic waves in an internally heated rotating fluid annulus: a case of wave/vortex duality?

1997 ◽  
Vol 337 ◽  
pp. 155-191 ◽  
Author(s):  
P. L. READ ◽  
S. R. LEWIS ◽  
R. HIDE
Keyword(s):  
Numerical Simulations ◽  
Potential Vorticity ◽  
Axisymmetric Flow ◽  
Zonal Flow ◽  
Chaotic Advection ◽  
Rotating Fluid ◽  
Mean Flow ◽  
Baroclinic Waves ◽  
Vortex Merging ◽  
Flow Components

The structure, transport properties and regimes of flow exhibited in a rotating fluid annulus, subject to internal heating and sidewall cooling, are studied both in the laboratory and in numerical simulations. The performance of the numerical model is verified quantitatively to within a few per cent in several cases by direct comparison with measurements in the laboratory of temperature and horizontal velocity fields in the axisymmetric and regular wave regimes. The basic azimuthal mean flow produced by this distribution of heat sources and sinks leads to strips of potential vorticity in which the radial gradient of potential vorticity changes sign in both the vertical and horizontal directions. From diagnosis of the energy budget of numerical simulations, the principal instability of the flow is shown to be predominantly baroclinic in nature, though with a non-negligible contribution towards the maintenance of the non-axisymmetric flow components from the barotropic wave–zonal flow interaction. The structure of the regime diagram for the internally heated baroclinic waves is shown to have some aspects in common with conventional wall-heated annulus waves, but the former shows no evidence for time-dependence in the form of ‘amplitude vacillation’. Internally heated flows instead evidently prefer to make transitions between wavenumbers in the regular regime via a form of vortex merging and/or splitting, indicating a mixed vortex/wave character to the non-axisymmetric flows in this system. The transition towards irregular flow occurs via a form of wavenumber vacillation, also involving vortex splitting and merging events. Baroclinic eddies are shown to develop from an initial axisymmetric flow via a mixed sinuous/varicose instability, leading to the formation of detached vortices of the same sign as the ambient axisymmetric potential vorticity at that level, in a manner which resembles recent simulations of atmospheric baroclinic frontal instability and varicose barotropic instabilities. Dye tracer experiments confirm the mixed wave/vortex character of the equilibrated instabilities, and exhibit chaotic advection in time-dependent flows.

On hydromagnetic waves in a stratified rotating incompressible fluid

1969 ◽  
Vol 39 (2) ◽  
pp. 283-287 ◽  
Author(s):  
R. Hide
Keyword(s):  
Incompressible Fluid ◽  
Angular Speed ◽  
Density Stratification ◽  
Stratified Fluids ◽  
Rotating Fluid ◽  
Rotating Fluids ◽  
Hydrodynamic Behaviour ◽  
Dispersion Relationship ◽  
Hydromagnetic Waves ◽  
Made In

The dispersion relationship for plane hydromagnetic waves in a stratified rotating fluid (α) indicates that the well-known analogy between rotating fluids and stratified fluids in regard to their hydrodynamic behaviour does not extend to magnetohydrodynamic behaviour, and (b) lends credence to a certain conjecture made in a previous paper, namely that effects due to density stratification can be neglected when considering the dispersion relationship for free hydromagnetic oscillations of the Earth's core if the Brunt—Väisälä frequency is much less than twice the angular speed of the Earth's rotation.

scholarly journals The Nutations of Neutron Stars and Core-Crust Coupling

1987 ◽  
Vol 125 ◽  
pp. 454-454
Author(s):  
C. R. Gwinn
Keyword(s):  
Simple Model ◽  
Neutron Stars ◽  
Ideal Fluid ◽  
Density Stratification ◽  
Uniform Density ◽  
Rotating Fluid ◽  
The Core ◽  
Inertial Coupling ◽  
The Earth

Neutron stars, like the earth, are rotating fluid-filled ellipsoids. Poincaré (Bull. Astron. 27, 321, 1910), Hough (Phil. Trans. R. Soc. A186, 469, 1895) and others have discussed the nutations of such objects through a simple model, which treats the crust as rigid and the core as an ideal fluid of uniform density and vorticity. The core and crust are coupled by inertial coupling: the forces which constrain the fluid to its cavity within the crust can produce a net torque, since the cavity is ellipsoidal. Additional torques, and the effects of the elasticity in the crust and density stratification in the core, may be accomodated in such models as well (Sasao et al., Proc. IAU Symposium 78, p. 165, 1980, and references therein).

A note on the role of the buoyancy layer in a rotating stratified fluid

1971 ◽  
Vol 48 (1) ◽  
pp. 181-182 ◽  
Author(s):  
J. Pedlosky
Keyword(s):  
Boundary Layer ◽  
Fourier Series ◽  
Side Wall ◽  
Cylindrical Container ◽  
Rotating Fluid ◽  
Vertical Side ◽  
Dynamical Characteristics ◽  
Viscous Boundary ◽  
Rotating Stratified Fluid

In the theory of steady stratified rotating fluid motions developed by Barcilon & Pedlosky (1967) (hereafter referred to as B & P) for flows within a circular, cylindrical container it was asserted that the innermost boundary layer on the vertical side wall was absent to lowest order when the side wall is thermally insulated. That is to say, the buoyancy layer is not required to close the vertical mass flux. This result has been disputed in a recent note by Harrington & Johnson (1969) (hereafter referred to as H & J). It is the purpose of this note to reiterate the earlier result of B & P and to show that H & J is in error. Further the result is placed on firmer ground by using the fundamental dynamical characteristics of the inviscid interior and viscous boundary layers and by avoiding the algebraic snares of manipulating Fourier series.

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