Combined Effects Of Rotation Research Articles

THE REDUCTION OF DIFFUSION BY PLASMA ROTATION AND ION DISSIPATIVE EFFECTS

The authors show that the combined effects of rotation, ion-viscosity and ion-neutral friction reduce the particle transport substantially for positive rotation and enhance the transport for negative rotation. Consequently, there exists a weak axial gradient in a cylindrical geometry with identical electrodes (at the cathode the plasma is hotter and denser than at the anode). The authors also show that because of these effects the particle confinement was appreciably better than the classical and Nernst effect

Turbulent thermal convection in the presence of rotation and a magnetic field: A heuristic theory

Abstract The growth of linear, Boussinesq convective modes for a superadiabatic fluid in a planar geometry with negligible thermal diffusion or molecular viscosity is analysed. Small and large magnetic diffusivity limits are both considered. A finite amplitude theory is constructed by assuming that non-linearities (e.g. shear instabilities) limit the flow amplitude, and the dominant modes are assumed to he those which transport most heat. This leads to a unique prescription for the average velocity, superadiabaticity and horizontal lengthscale as a function of the imposed heat flux, rotation rate, large scale magnetic field and vertical lengthscale. Simple analytical results are provided (in terms of the relevant dimensionless numbers) which are as easy to apply as the conventional mixing length theory (MLT). The conclusions are: (i) For no rotation or magnetic field, the model reproduces MLT except that it predicts about an order of magnitude lower heat flux. (ii) Rotation alone or magnetic field alone inhibits the convection. For a given heat flux, the convective velocity and horizontal wavelength are reduced, and the temperature gradient increases. (iii) If R o≲0.1, where R o is the nominal Rossby number, then the combined effect of rotation and magnetic field enhances the convection, and the maximum heat flux occurs at non-zero field. (iv) The rotational inhibition of convection in rapidly rotating stars does not substantially modify their static structure. (v) Convective velocities of around 0.02 cm/sec are predicted for the Earth’s core, consistent with geomagnetic secular variation timescales, provided the toroidal field is less than about three times the poloidal field. (vi) In both the Earth and Jupiter, the actual magnetic field is within an order of magnitude of the field which minimizes the temperature gradient for a given heat flux. Application of these results to stellar and planetary dynamos is briefly discussed and critically assessed.

MHD instability of rotating superposed fluids through porous medium

The present paper is an investigation to study the effect of magnetic field and rotation on the stability of two superposed fluids through porous medium. For the case of no magnetic field, the simultaneous presence of rotation and permeability makes the system unstable. For non-rotating configuration, the magnetic field is found to have stabilizing effect on the system under consideration. The combined effect of rotation and magnetic field on the stability of superposed fluids through porous medium is also discussed.

Motion of a sphere in an electrically conducting rotating fluid

The combined effect of rotation and magnetic field is investigated for the axisymmetric flow due to the motion of a sphere in an inviscid, incompressible electrically conducting fluid having uniform rotation far upstream. The steady-state linearized equations contain a single parameter α=1/2βRm, β being the magnetic pressure number and Rm the magnetic Reynolds number. The complete solution for the flow field and magnetic field is obtained and the distribution of vorticity and current density is found. The induced vorticity is O(α4) and the current density is O(Rm) on the sphere.

A Numerical Example of the Collapse of a Rotating Magnetized Star

view Abstract Citations (448) References (5) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Numerical Example of the Collapse of a Rotating Magnetized Star LeBlanc, J. M. ; Wilson, J. R. Abstract The time history of a star of 7 M0. undergoing gravitational collapse due to iron decomposition is calculated numerically. The angular velocity assumes a vortezlike distribution which halts the collapse at a relatively low density, 1011 g . The large shear in the velocity field gives an enhancement of about 100 in the multiplication of magnetic-field energy over the energy multiplication from simple compression. The combined effect of rotation and magnetic field is to produce an axial jet. At a radius of 4 X 10 cm where the jet material leaves the calculational grid, the jet carries a mass of 2.1 X 1031 g and a total energy of 1.6 X 1050 ergs. The energy is principally kinetic, 1.6 X 10 ergs, but it also has a large magnetic energy equal to 3.5 X 10 ergs, and only 1.1 X 10 ergs of internal energy. Publication: The Astrophysical Journal Pub Date: August 1970 DOI: 10.1086/150558 Bibcode: 1970ApJ...161..541L full text sources ADS |

Heat Transfer From a Rotating Cylinder With and Without Crossflow

Abstract In this paper the problem of convection heat transfer from a rotating cylinder is extended to the case of a cross, or normal flow to the cylinder. Experimental heat-transfer data are presented for a cylinder rotating with and without crossflow. The data for the cylinder rotating with no crossflow are in substantial agreement with the results of previous work, and also with the results of a heat-and-momentum-transfer-analogy solution for convection with no crossflow. Measured temperature profiles in the boundary layer of the heated rotating cylinder are in very good agreement with the analogy solution, and indicate that the boundary layer on a rotating cylinder is quite similar to a turbulent boundary layer on a stationary surface out to about y+ = 20. Thereafter a secondary flow becomes the controlling mechanism. The experiments with combined rotation and crossflow indicate two flow regimes; the first for the cylinder peripheral velocity less than twice the crossflow velocity, in which the crossflow provides the controlling effects; the second for the cylinder peripheral velocity greater than twice the crossflow velocity, in which there is a continuous boundary layer around the cylinder and the rotational velocity provides the controlling effects on heat transfer. It is shown that the combined effects of rotation, free convection, and crossflow can be correlated by the equation NNu=0.135[(0.5NR2+NRs2+NGr)NPr]1/3 for the rotating Reynolds number in the range 2000 to 45,000.

Hydrodynamic forces acting on a cylinder in motion, and the idea of a "hydrodynamic centre."

There are two general methods of determining the forces acting on a cylinder due to the two-dimensional motion of a surrounding liquid. One is applicable to the case of a stationary cylinder in a stream, in the form X - Y = 1/2 p ∫( dw / dz ) 2 dz . (1.1) M = -1/2 pR ∫( dw / dz ) 2 z . dz (1.2) where X and Y are the components of the resultant force, parallel to the x and y axes, and M is its moment about tbs origin; p is the density of the fluid, and w is the velocity potential-stream-function for the fluid motion; z is as usual the complex variable x + y . The other is that obtained from the general theory of the "impulse. The first of these is unable to deal with a rotating cylinder, and the second is unable to include "circulation." In the course of an investigation of the effects of rotation upon the circulation round, and the forces acting upon, a Joukowski aerofoil, to which problem neither method applies, since the combined effect of rotation and circulation is needed, a quite general result was obtained, which it is thought worth while to publish separately.